Anyone know what the "tiny terror" circuit is?

[FatGaz]

Hi all,

I've got a old project amp that I want to rebuild - I was never happy with the design i tried SO i want to strip it down and try again.

Anyhow, the amp has two 12ax7's and 2 EL84s plus an EZ80 or EZ81. At the moment it has the power stage arranged as one 12ax7 as a phase splitter into the two el84's using i think the circuit of a marshall 18 watt amp. The pre is the two triode stages of the other 12ax7 in series with a tone stack in between. The preamp was my own design; unfortunately it sucked !

I happened to try an orange tiny terror amp in a shop last week - WOW this is just what i want my amp to sound like !!!

anyone know what circuit it uses ? it's got the same set of tubes - but uses a SS rectifier.

(also my amp happens looks very similar to the tiny terror - it's a shoebox sized metal head with a handle on top)

Anyone know if orange are in the habit of including schematics with their amps ?

Peace and Season's greeting,

Gareth.

[FatGaz]

http://www.orangeamps.com/tinyterror/

only info i have been able to find on the web is from this link (and it's a very interesting description of an amp design possibly closer to the kind of tricks 'london power' amps use than a basic circuit from an ac15 or 18-watter etc.)

http://www.musicianshotline.com/issue/features/200701_product_orangeusa.asp

from which i quote :

"Inventing Terror
The Tiny Terror utilizes class A valve technology with a 100% analog signal path that eliminates any and all digital clipping output characteristics. Driven by a pair of EL84 power valves and a front end that utilizes a duct of 12AX7 preamp valves. Switchable from 7 to 15 watts of output, Orange designers have designed the gain structure of the Tiny Terror to work in a very unique way; utilizing a dual gang gain pot, one side turns up the first gain stage to the point of very heavy compression, while the other side changes the impedance of the second gain stage so that it to compresses to the same degree.

It utilizes a five section fully filmed interleaved output transformer that is very closely balanced to primary. The EL84 output tubes are cathode biased to around 90% in the 15w position, and 96% in the 7w position. In short, the Tiny Terror is designed to produce as much gain as a four stage gain pot, but the output tubes are driven evenly all the way through. The tone control is also designed in a unique way, where the tone circuit is not on the preamp side, but actually part of the phase inverter (power amp) so the gain structure of the amp is unaffected by the tone control. "

[AdmiralB]

It's an AC15, with an extra gain stage cascaded on the front end. PI and power amp are 100% AC15. The gain pot is a dual 500K that serves as simultaneous voltage dividers after each gain stage.

The amp is actually biased at over 15W per tube static. It's insane. I swapped the 100 ohm cathode resistor for a 180 ohm, made no difference in the sound but made the tubes a lot happier.

[steve]

Admiral,

How does the 7/15 watt switch work?

steve


It's an AC15, with an extra gain stage cascaded on the front end. PI and power amp are 100% AC15. The gain pot is a dual 500K that serves as simultaneous voltage dividers after each gain stage.

The amp is actually biased at over 15W per tube static. It's insane. I swapped the 100 ohm cathode resistor for a 180 ohm, made no difference in the sound but made the tubes a lot happier.

[AdmiralB]

It selects a different HV tap on the PT secondary. One leg remains tied to one side of the bridge rectifier, the other side has two taps and the switch selects between them. The result is something like 250VDC rather than about 325VDC.

It affects the entire amp, not just the power tubes, and it does NOT do anything to the bias state - so, in stock form the amp is severely (IMO) underbiased in 15W mode, and just about right in 7W. But I think the low voltages affect the feel in a negative way.

I replaced the power switch with a DPDT and also switched a second cathode resistor in parallel when I selected 7W. That made both modes idle happily.

[steve]

Cool. Thanks for the info.

steve

It selects a different HV tap on the PT secondary. One leg remains tied to one side of the bridge rectifier, the other side has two taps and the switch selects between them. The result is something like 250VDC rather than about 325VDC.

It affects the entire amp, not just the power tubes, and it does NOT do anything to the bias state - so, in stock form the amp is severely (IMO) underbiased in 15W mode, and just about right in 7W. But I think the low voltages affect the feel in a negative way.

I replaced the power switch with a DPDT and also switched a second cathode resistor in parallel when I selected 7W. That made both modes idle happily.

[Steve Conner]

That's "underbiased" as in running too hot, I guess? I always think of underbias as meaning cold with a lack of idle current.

BTW, thanks for the info, I played through one of these in a guitar shop a while back, and was wondering how they were made. It struck me as a real dirt machine of an amp. I read all the PR blurb on the Orange site, and it gave me the impression of some top secret cutting-edge technology, not an AC15 clone ;-)

[bob p]

It selects a different HV tap on the PT secondary. ... the switch selects between them. The result is something like 250VDC rather than about 325VDC.
didn't Randall Smith/Mesa claim a patent for B+ switching back when they first used that in the Mark series amps? I know that my Mk IV uses a toggle switch to tap different coils on the PT for its lower voltage "tweed" mode, and its higher voltage "full power" mode. IIs Orange licensing that, or has that patent expired already?

[AdmiralB]

didn't Randall Smith/Mesa claim a patent for B+ switching back when they first used that in the Mark series amps? I know that my Mk IV uses a toggle switch to tap different coils on the PT for its lower voltage "tweed" mode, and its higher voltage "full power" mode. IIs Orange licensing that, or has that patent expired already?

Smith's patent selects different taps on the primary - in practice, one is 120V and the other is around 160V, which when fed 120V gives the result of 120V variaced down to about 90V. It browns out the whole amp, HV, heaters, bias, etc.

The TT switches the HV secondary only. Heaters don't change.

[drewl]

Judging from the assesment, it seems pretty close to the rocker series....here's one I had to bring back from the dead.....it blowed up real good!

http://img.photobucket.com/albums/v360/drewl1/100_1918.jpg

http://img.photobucket.com/albums/v360/drewl1/amps/100_1917.jpg

[gtrboy]

please post the schematic on this one... it kicks butt!!! i played one. its gotta have 3 gain stages and not be push pull. the dual pot thing has been on ax84 forever. no news there.

[AdmiralB]

Ask and ye shall... (http://r.clear.home.insightbb.com/OTT.pdf)

gotta have 3 gain stages and not be push pull.

Why do you say this? It is neither of those things.

[gtrboy]

thats one sexy circuit!!

[mak]

so, has anyone tried to mod the tone circuit to brighten the mid/hi response? great amp, but a really foggy tone and not much authority in the tone circuit
Cheers
mak

[FatGaz]

Hi All,

I've not been here for a while after posting my query - but ampage proves what a fantastic set of people post here ! both the circuit and constructive critisism of it !

I am now spurred-on to get the soldering iron out and turn my failed project amp in to a terrible-tot !

I using a hammond universal PP OT, 125E i think is the model number. I have a tube recto too (ez80 i think) so the amp will probably feel fairly different.

Questions for A.B. re the schematic....

I notice that there is the 7/15w hv switch is not shown and that there is also no master vol shown - which master vol circuit is used ? post PI ?

I will mod my preamp to match that of the circuit and put two preamp gain controls in. I will leave my poweramp as is - it has switchable NF and a post PI master vol that shorts across the power tube outputs. I'm not sure if i'll bother putting in the ac-15 alike top-cut.

I don't have any dual 500K or 1mge pots at the moment - maplin don't do them worst luck - so i'll need to think what els i need for a big enought mailorder.

If anyone has any ideas about tweaks i might want to do or where I may need to tweak component values to suit my particuar tubes/ ot/ B+, post them here !

Gaerth.

PS
since i last posted i've hot rodded my jap squire strat (kinman woodstock plus pups and a switch to put the bridge pup in series) and finally set it up properly with a new bone nut, bridge bits and I read a decent book and borrowed an imperial feeler guage to set it just right - it's such a better guitar now - bridge and neck in series is a great new tone too. :)

[AdmiralB]

You're right, I omitted the master from my drawing. It's a 500K dual-pot post-PI master with an extra set of .1uF caps.

The power switch is on my drawing, it's on the HV secondary. It selects between two 'ends' of the winding - HV winds up with about 325V and LV about 250V.

[AdmiralB]

I fixed the drawing. Standard post-PI master, but since it's cathode-bias it doesn't need the extra set of blocking caps.

[ElTeye]

I picked up a TT, and was very pleasantly surprised with the build quality. It sounds nice; now on to the fine tweaking!

1) The 7/15Watt switch:
It affects the entire amp, not just the power tubes, and it does NOT do anything to the bias state - so, in stock form the amp is severely (IMO) underbiased in 15W mode, and just about right in 7W. But I think the low voltages affect the feel in a negative way.

Would it be an improvement if the 7/15W switch just lowered the power tubes and left the pre-amp in hi-volt mode? That would be tricky to achieve, right?
Cathode bias R is R5? I read somewhere it would be better a 180-Ohm resistor. Would it not be better to switch this value also when switching from 7 to 15 Watt?
Admiral, what values of cat resistor and bypass cap do you suggest for the 7 Watt, and which for the 15 Watt position?

2) The resistors seem to be metal film in the first stages - nice - but all caps are little square blue boxes. Would it be a big improvement if I replaced a bunch with SoZo caps? If so, which ones to replace for max effect?

3) On every single TT I've seen, one of the transformers sits crooked. Does this have a reason? Seems weird for such a neatly built amp!

Thanks so much,

El Teye

[AdmiralB]

I don't know how you'd affect only the voltage in the power amp since the switch selects a different HV tap on the power transformer.

180 ohms is a good choice at 15W power; I replaced the power select switch in mine with a DPDT (Mouser sells the same switch brand and family) and used the other pole to place a 100 ohm resistor in parallel with the 180 when I went down in power. Worked great.

I don't think there's much to gain with cap swaps, myself. And both of my transformers were crooked too!

[ElTeye]

Hello Admiral and thanks for your quick reply! The soldering iron, as well as my modding desires, are itchy!

I don't know how you'd affect only the voltage in the power amp since the switch selects a different HV tap on the power transformer.
Theoretically, you could leave the voltage drop resistor circuitry hooked up to the 325? And run a new wire that switches the power section and its resistor only? Would probably involve some doubling of some parts. Might affect the whole sound of the whole thing and thereby defeating the concept.
Perhaps a TPDT 7/15Watt switch, altering (or shorting) voltage drop resistor to the pre-amp, as well as transformer tap and cathode resistor?
Or is that just going too far?
(i)I'd thought this beast was a single-ended amp, and you could just pull 1 EL84 ! (At these power ratings, impedance matching does not worry me too much: I've built a AC15 w AC30 front end, put two 10" speakers in series to connect to the 16Ohm tap, and really the thing sounds MUCH better running them parallel into the 8-Ohm tap. Have been doing so for many years now. OT doesn't even get warm.)(/i)


180 ohms is a good choice at 15W power; I replaced the power select switch in mine with a DPDT (Mouser sells the same switch brand and family) and used the other pole to place a 100 ohm resistor in parallel with the 180 when I went down in power. Worked great.
Fantastic tip! Thanks! Saves a lot of guessing and trying. Thank you so much!

I don't think there's much to gain with cap swaps, myself.
The thing sounds really good as is! But it's all PCB mount so then I wonder: do those blue box caps sit there for sound, or for reasons of easy mounting? Have rebuilt several amps with better caps and the result has been very pleasing, without exception. If I do so, I will let you know my findings OK?

And both of my transformers were crooked too!
I straightened out mine last night. It's just the final touch, but.... weird.

Thanks Admiral!

Teye

[AdmiralB]

The voltage selection isn't choosing "both ends" of a winding, one side is always connected to the bridge and the other is selected by switch. I don't know how well adding a second bridge, as well as filter bank(s), would work. IMO, not worth the trouble considering what it is.

The box caps are there I suspect because they're easy for machines to stuff.

[ElTeye]

The voltage selection isn't choosing "both ends" of a winding, one side is always connected to the bridge and the other is selected by switch. I don't know how well adding a second bridge, as well as filter bank(s), would work. IMO, not worth the trouble considering what it is.

The box caps are there I suspect because they're easy for machines to stuff.

Of course! It's not switching the DC but AC voltage! Oh man, the brain... sorry.

Still, I could experiment with altering the voltage drop resistor to restore at least some of the voltage back to the pre-amp section... Interesting thing is that I HAVE some TPDT switches at the house (big ones, not micro...)

I'll give the amp some burn-in time and then probably put SoZo caps in, just for giggles.

Hey Admiral, do you hav e that schematic please? Can you e it to teye@teye.com? I'd be helped big-time!

Thanks,

Teye

[ElTeye]

The amp is actually biased at over 15W per tube static. It's insane. I swapped the 100 ohm cathode resistor for a 180 ohm, made no difference in the sound but made the tubes a lot happier.

I did the recommended mod to let the tubes run a little cooler: put in the 180 Ohm cathode resistor, switching in a parallel 100 Ohm when giong to 7 Watts. My amp lost punch, bite, and some volume in the 15Watt setting. Even trying some in-between values (connecting a few parallel resistors: i did all of this while the amp was on and I was all plugged in) still did not restore the full blast.

I quickly moded it back to original. Can't believe it: ME happy with the stock version?

Sound-wise: the pre-amp tubes are good quality JJ ECC83's. No reason to not experiment though!
I got a slightly more Ampeg feel by using a 7025 long plate for V1 and 12AU7 for the PI (little surprise there, really). Tried a 12AT7 for PI and was not happy.
My favorite: a Watford tubes Cyrogenically treated ECC83 for V1, and... a long plate 7025 for V2. I would describe it as a middle-of-the-Atlantic sound....

[haripotna]

I did the recommended mod to let the tubes run a little cooler: put in the 180 Ohm cathode resistor, switching in a parallel 100 Ohm when giong to 7 Watts.

Why don't you put a 360 E resistor in parallel to the 180 E cathode resistor in 7 Watt mode - in this case the overall value would be 120 E for 7 Watt mode ?

I wanna mod the circuit by building in a solo-switch and clean-(less gain)-switch...
...any suggestions ?

[AdmiralB]

That's what I did - I put a new power switch in (DPDT, replacing the stock SPDT) and brought in a second resistor. But I used 100 ohms, which got me in the right spot dissipation-wise. 120 is too high for 7W mode.

I can't explain why he heard such a dramatic difference. I heard none at all.

[ElTeye]

That's what I did - I put a new power switch in (DPDT, replacing the stock SPDT) and brought in a second resistor. But I used 100 ohms, which got me in the right spot dissipation-wise. 120 is too high for 7W mode.

I can't explain why he heard such a dramatic difference. I heard none at all.

Yes it is weird. Because I heard it immediately, and at an ungodly hour too! So, to be certain, I wired it all up so that I could switch back and forth between the 180 Ohm and the 120 (and also some in-between values, by means of some parallel resistors, All soldered together on one side, and hook-uppable via clamps).

When going from the 120 to 180, I lost (very audibly so): power, some edge/bite, and all-in-all the eagerness of that amp that I love so much. Even on the in-between valkues, I could not get the result that I got from the 120.

I used a 1993 Tony Zemaitis Custom Deluxe guitar for the tests. Very responsive guitar. And plugged it into a Scumback "Pre-Rola" Celestion loaded 1x12 GenzBenz closed back cab. All very hi quality stuff, and with the Tiny Terror back to stock, a delight to play thru.

Normally, I cannot wait to get the soldering iron into modern stock stuff cause I know that upgrading it is usually just a matter of removing cost-cutting factors (like a SPDT switch....)
But in this case, I'll just keep it stock. I'm very happy for Admiral that in his TT there is no sound difference so that you can run those tubes cooler! Wish I could too! Mine (probably due to many other tolerances in the amp) cannot, so I'll just run it HOT baby yeah!

Next up, I will replace the coupling caps with SoZo's. Will let you know how that goes (it'll be some time though).

Greetings to all!

Best,

Teye

[Justin]

I was wondering if someone could repost the schematic the link to it is broken. Thanks

[AdmiralB]

It works now, my ISP is a little flaky at times.

[tbryanh]

didn't Randall Smith/Mesa claim a patent for B+ switching back when they first used that in the Mark series amps? I know that my Mk IV uses a toggle switch to tap different coils on the PT for its lower voltage "tweed" mode, and its higher voltage "full power" mode. IIs Orange licensing that, or has that patent expired already?

A large number of patents are bogus.

The patent office is mostly a record-keeping office. They generally let industry fight it out to see if a patent is valid, otherwise it sits there uncontested.

The patent office generally does not decide if a patent is valid unless it is extremely obvious that it was already invented or is not novel.

Take the wheel for example.

If the patent office already recorded a patent for someone for inventing the wheel, they would not record a patent for you for this. It would be extremely obvious that the wheel was already invented. And, it they hadn't recorded a patent for someone else yet, they still would not do it for you. It would be extremely obvious that inventing the wheel is not novel.

A patent search to see if the "invention" already exists or is similar to one that already exists is required before a patent can be issued. But the patent office does not do the search. They require that the person applying for the patent to do the search.

Bottom line: If you are not "inventing" the wheel, you fill the paperwork out correctly, and you pay the fee, you get your "patent."

Most of the protection for electronic circuits comes from copyrights, not patents. The foil patern on a printed-circuit board is unique and can be copyrighted as art. Most companies copyright their artwork on their PC boards because it is easy to prosecute someone who copies it. When someone duplicates their PC boards, it is blatently obvious.

Randall Smith's patents are probably bogus.

[Steve A.]

It selects a different HV tap on the PT secondary. One leg remains tied to one side of the bridge rectifier, the other side has two taps and the switch selects between them. The result is something like 250VDC rather than about 325VDC.

It affects the entire amp, not just the power tubes, and it does NOT do anything to the bias state - so, in stock form the amp is severely (IMO) underbiased in 15W mode, and just about right in 7W. But I think the low voltages affect the feel in a negative way.

I replaced the power switch with a DPDT and also switched a second cathode resistor in parallel when I selected 7W. That made both modes idle happily.

Aunt Bea, er, I mean *Admiral B*:

So the 325vdc and 250vdc voltages you mentioned would be the B+ from the first node of the power supply? Just checking...

I like the idea of using separate taps rather than padding the voltage with a resistor, which can get downright mushy. Then again we could always use the Bruce Collins 10v/5w zener diode trick to cut the B+ down a little bit...

Thanks!!!

Steve Ahola

[AdmiralB]

Right. Since it's a bridge rectifier, there are no 'symmetry' issues around a center tap (there is no center tap), and only one side of the HV winding is switched.

[Wicksy]

Hey AdmiralB, i just though i'd pop by and say thanks for the schem! I'm building a handwired clone. I'm going the whole hog using TAD mustard clones etc... From your schem i managed to draw up a nice layout. Cheers!

[haripotna]

Greets.

I'd like to add an eq after the input stage to the curcuit, in order to have more control over my tone (take some mids out, etc.).

I would build out the resistors R22 (68k) and R23 (470k) and put an eq like used in the mesa/boogie caliber 50 instead of it.

What would you think about this modification ?
Any suggestions for a built in eq ?

[Steve A.]

Greets.

I'd like to add an eq after the input stage to the curcuit, in order to have more control over my tone (take some mids out, etc.).

I would build out the resistors R22 (68k) and R23 (470k) and put an eq like used in the mesa/boogie caliber 50 instead of it.

What would you think about this modification ?
Any suggestions for a built in eq ?

My drawing for a .50 Caliber + shows both a BF style tone stack and a graphic equalizer. What did you have in mind?

Adding a regular tone stack to the TT would cut the overall gain something like 20dB. If you need additional control over the tone I'd suggest a tweed deluxe style tone control, wired up to a switch to be able to remove it from the circuit completely.

The thing I liked about the TT was that it was so simple and direct- without all of the BS that you typically find in a Mesa Boogie amp...

Good luck!

Steve Ahola

[haripotna]

Well, I'd like to add a traditional tone stack to the circuit in order to have more control over the sound. I love the basic sound of the amp, but I'm more the rock/metal head, so I need to shape the sound (just a bit).

I consider, adding a switch to cut the mid-pot of the ground for having a solo switch (without eq in solo mode).

I've put 4 leads instead of the 68k(100k) and the 220k resistor before the second stage of the gain pot - now I can try out several circuits without having to dismount the amp each time I try out an other mod.

I think, I'll give the deluxe tone control a try, for it is very simple and has got good reviews for its "versatility".

Greets from Austria !

[Shark_Sandwich]

I'm considering converting an old PA amp (2 x 12AX7, 2 x EL84) to a Tiny Terror circuit. Does anybody know what plate voltages are run to the tubes?

Thanks,

Don

[axpro]

Just started playing with one of these... nice little amp, and i kinda like the extra crunch in the pre as opposed to my 18 watter, but this amp DOES NOT like my 15" big ben cab! got a little upper mid sizzle that just irks me, don't hear it with a 12" cab, but it doesn't like the big ben. my 18 likes it fine, my single ended champs like it fine,a nd my long lost Drz Z-28 loved it....

Tried pulling the bright cap, to cut some of the high end (so subjective, and other people want MORE upper mids?!?!?)

It helped a bit, but not too much.... just seems to get going when i crank the preamp above 3/4 or so. Pull back the pre, and goose up the master, and it is fine, but loses that grind.... any other ideas? like Steve A I like the simplicity of the circuit as-is, but i may have to add a tone control somewhere.... good call with the deluxe style... I can put it on a push pull or something..... hmmmmmmmmmmmmmmmmmm
:D

[axpro]

So, changed the Cathode resistor in the phase inverter 9was 1.2k, put a 1.k in parallel for theoretical 550 ohms)

The "fizzyness of the top end is gone now, but i think i have to reconnect the bright cap... since the only tone control is a "cut" control, it has less effect when the gain is lower, as there is less high end content in the source... we'll see how it goes tomorrow, ill try a few alternate bright caps.

[pippodepippis]

Hi boys,
I'm trying to do by myself something playing like "little bastard" tiny terror.
Can you post me schematic?
kkobain@tiscali.it

[kjellpropell]

Hi , I`m thinking of making a TT clone for my brother, and he directed me to this tread. I`ve made a layout from the schem that admiral B posted, but can anyone tell me what the secondary voltages on the PT are in the real TT, and is there something mysterious about the OT ?

Kind regards

Kjell

[Valvehead]

i had a similar question, what transformers can be used for this project ? something from Hammond ?

[princecharlz]

Good modification that only involves a tube change. I had a 60's RCA 12au7 tube sitting around so I thought I would put it in my new Tiny Terror. That tube made the amp what I wanted it to be. Before, the amp got ridiculously overdriven. It sounded more like a novelty amp... class-a amp with a boss orange distortion. (I wonder if that's were boss got the color from on the ds-1 because it sounds remarkably similar). So I was a little unhappy with the distortion pedal effect, because I like my distortion pedals, and was kind of hoping this would break up in a slower more "amp-like" way. I guess how I imagined an old vox cranked or something. When I put in the au7... OMG. This amp sounds fantastic!!! It reduces the overall output of the amp, which leads me to think I'm basically putting a "stopper" on the amp's gain at 6 or 7 (not o'clock but as in 5 being center, ten being max). Which is probably the case, but, it's like 7 becomes 10 now, which is the perfect tone for me, but I have 10 numbers to tweak the sound now. I can get a lot more room when I dial in, where as before, it seemed like from 5 to 6 it suddenly got really dirty. Now I get that same pallette of dirt between, 6 and 8. And between 9 and 10 is this great distortion that's more than enough for my liking. This simple mod is soooo great, try it if you think the TT is a little to much and want a great vintage tone. Also there are two tubes with more gain than the 12AU7 but less than the 12AX7. I think one is the 12AT7, I forget the other, but I would love to try those out, to bridge the gap. The tube I changed was the one on the right side of the amp while looking at the name-plate. The one on the left side didn't seem to make as much of a difference (if any).

[s.r.v.]

hey guys!
first post here!

so how many of you guys are also planning a Tiny Terror Build? I have a layout, but I'd like a few opinions, so Kjell can you please email me your layout? I'd really appreciate it
s4r4v4 @ aim.com

Right now, I'm just piecing through a layout with the schematic. so far so good, but i'm sure i'll have some serious debugging if i ever get around to it!

[Steve A.]

hey guys!
first post here!

so how many of you guys are also planning a Tiny Terror Build? I have a layout, but I'd like a few opinions, so Kjell can you please email me your layout? I'd really appreciate it
s4r4v4 @ aim.com

Right now, I'm just piecing through a layout with the schematic. so far so good, but i'm sure i'll have some serious debugging if i ever get around to it!

Thanks for bringing this up! I have a few Epi Valve Jr's and Tube 30's around and was planning to try out a TT design in one of them. There are so few parts (other than the power supply) that I think it should be fairly easy to design an eyelet board for it- or even use perfboard.

As for the comments about a tone stack, I really think that a few well-placed, well-chosen caps and/or resistors could fine-tune this amp to work with your intended cabinet. Or maybe just go with a 5E3 tone control, since it doesn't have the 20dB loss of a blackface style tone stack (I think that you can switch it out of the circuit with a DPDT switch).

Steve Ahola

P.S. Another project I've been seriously considering for my menagerie of Epiphonia is the JonesAmps 3 Tube SE Wreck that I guess was very popular with the AX84 folk. But the intended host for that circuit is a Galaxie 10, not a Valve Jr or Tube 30...

[OrangeTT]

Good modification that only involves a tube change. I had a 60's RCA 12au7 tube sitting around so I thought I would put it in my new Tiny Terror. That tube made the amp what I wanted it to be. Before, the amp got ridiculously overdriven. It sounded more like a novelty amp... class-a amp with a boss orange distortion. (I wonder if that's were boss got the color from on the ds-1 because it sounds remarkably similar). So I was a little unhappy with the distortion pedal effect, because I like my distortion pedals, and was kind of hoping this would break up in a slower more "amp-like" way. I guess how I imagined an old vox cranked or something. When I put in the au7... OMG. This amp sounds fantastic!!! It reduces the overall output of the amp, which leads me to think I'm basically putting a "stopper" on the amp's gain at 6 or 7 (not o'clock but as in 5 being center, ten being max). Which is probably the case, but, it's like 7 becomes 10 now, which is the perfect tone for me, but I have 10 numbers to tweak the sound now. I can get a lot more room when I dial in, where as before, it seemed like from 5 to 6 it suddenly got really dirty. Now I get that same pallette of dirt between, 6 and 8. And between 9 and 10 is this great distortion that's more than enough for my liking. This simple mod is soooo great, try it if you think the TT is a little to much and want a great vintage tone. Also there are two tubes with more gain than the 12AU7 but less than the 12AX7. I think one is the 12AT7, I forget the other, but I would love to try those out, to bridge the gap. The tube I changed was the one on the right side of the amp while looking at the name-plate. The one on the left side didn't seem to make as much of a difference (if any).
Howdy!
First poster, just digging all the info on my fab little Orange.
I, too, tried the 12au7 swap, but on the other socket. With the knobs facing me, I did not know which of the 2 sockets was the preamp and which was the phase inverter, so I tried each one:
* trying the 12au7 in the right side made the amp almost inaudible
* trying it in the left side did exactly what I wanted: less grunge, more detail!
I did lose out on a wee bit of sparkle, but that's probably the difference between the good, stock Czech 12ax7 and the mezza-mezza Chinese 12au7. I imagine if I can get a really *nice* 12au7, then I'll get everything the Ruby gave me plus some sheen as well.

[Thomeeque]

Ask and ye shall... (http://r.clear.home.insightbb.com/OTT.pdf)



Why do you say this? It is neither of those things.
Hi AdmiralB & others!

I have two questions to OTT circuitry (OTT.pdf):

1) What is that switch between + pole of filtering 100uF cap and 150/5W resistor (and "A" line)? Normally I would say that this is the STAND-BY switch, however as I understand it, the "15/7" On-Off-On switch handles STAND-BY as well, so..?

2) To dual-gang logarithmic VOLUME pot - how critical is tracking quality of the pot-couple at this point of circuit? As I see it, the bad tracking could unballance power tubes (but I have no idea, how "fatal" will be circumstances for the rersultant tone), so I'm just wondering if I should not pick linear dual-gang pot (which has usually better tracking) instead, when I have doubts about tracking quality of pots available to me - thanks to following 220k resistors it will get bit "logarithmic" too (see Better Volume Control (http://sound.westhost.com/project01.htm)), but on the other hand I want to stay as close as possible to original circuitry.

Thanks, Thmq

[AdmiralB]

1) What is that switch between + pole of filtering 100uF cap and 150/5W resistor (and "A" line)? Normally I would say that this is the STAND-BY switch, however as I understand it, the "15/7" On-Off-On switch handles STAND-BY as well, so..?

I had an early amp. The first runs had a DPDT center-on three-position power switch - off, standby, on. The current amps have a three-position power switch that selects either HV tap - or neither, for standby.



2) To dual-gang logarithmic VOLUME pot - how critical is tracking quality of the pot-couple at this point of circuit?

IMO, not very. I don't think linearity means a whole lot WRT guitar amps.

[Thomeeque]

I had an early amp. The first runs had a DPDT center-on three-position power switch - off, standby, on. The current amps have a three-position power switch that selects either HV tap - or neither, for standby.


OK, this explains "strange" placing of STBY label on the picture below I have not understand up to now :) Thanks!

http://www.themusicfarm.com/images/products/small/tinyterror.jpg

[Bruce / Mission Amps]

I don't know if anyone mentioned it but that off-stdby-on switch is called a progressive toggle switch.
MOJO use to sell them if you need one, but if you wire a standard DPDT switch correctly, it will do the same thing but be OFF in the middle.
Or... toggle down = standby, toggle in the middle = OFF and Toggle up = AMP ON.

[Rick Erickson]

Smith's patent selects different taps on the primary - in practice, one is 120V and the other is around 160V, which when fed 120V gives the result of 120V variaced down to about 90V. It browns out the whole amp, HV, heaters, bias, etc.

He got a patent for that? My Greytop JMI AC-30 has a switch that does exactly that and I have used it for that purpose. This is a great example of my belief, that many of Smith's "patents" wouldn't stand up in court if someone were to seriously challenge him.

RE

[FatGaz]

Thanks for bringing this up! I have a few Epi Valve Jr's and Tube 30's around and was planning to try out a TT design in one of them. There are so few parts (other than the power supply) that I think it should be fairly easy to design an eyelet board for it- or even use perfboard.


Steve, all,

still haven't sorted that little amp of mine out yet - got side-tracked again....

BUT, regarding cheap little amps as donor fodder - thomann in the EU do a 2/3 price version of the EPI Valve Jr, and now they have a new super cheap combo amp :

http://www.thomann.de/gb/harley_benton_ga15.htm

I wonder what circuit this is ?

Gareth.

oh their valve jr. is :

http://www.thomann.de/gb/harley_benton_ga5.htm

[Thomeeque]

Hmmm, those Harley's are *sexy*!! :) Plus that price - it's not much more than a price of material for DIY project! :-O T.

[mathia]

Hi guys -
If anyone is interested, I can forward the OTT voltage chart, with readings taken from an actual OTT head. Lemme know.

[Thomeeque]

Hi! I'm definitely interested! Thanks, Thmq

[cheese]

me two! ARe there any suggestions what PT / OT can be used (Hammond ?)

[John G]

Hi,
I made a home brew of this one, and lack of top end, was a hinderence.
In the end I developed my own schem and moved away from the origional and installed passive Bass and assignable Treble controls.
Post your mail address or PM me if you are interested.
Cheers,
John G

[stavo]

Hi guys, yet another new poster here, i bought the tiny terror and all was ok until the gain control went a bit naff, ie at certain positions the output was hardly any at all and completely awfull sounding like a busted speaker, and now my problem as got even worse with no output at all, i have looked around the net but cant find anyone that supplies the a500k dual pot, so any ideas how i can get it up and running without this pot ie, fixed resistance instead perhaps? as i only ever used to like the setting of the gain at about 12 o clock, i guess that would equate to the pots resistance of about 250k? or does it not work like that with the logarithmic side of things? any help would be realy appreciated many thanks stavo......

[Thomeeque]

Hi Stavo! According to following picture:

http://www.geofex.com/article_folders/potsecrets/pottaper.gif

you should get approximately 90% of original A500k range by using A250K pot + 250k "starting" resistor (0.5 voltage division accords to 0.9 rotation fraction). Your favourite setting (0.5 rotation fraction) accords to 0.1 voltage division, so you will still have big reserve :)

Please note: real pot does not have ideal logarithmic course (curve 2 on pic), so the numbers I wrote above are just approximate, but exact accuracy is not point here. Check whole pot-story here: http://www.geofex.com/article_folders/potsecrets/potscret.htm

[Thomeeque]

But I'd advice to you to contact Orange first, they should be able to supply exact replacement pot.. ;)

[stavo]

But I'd advice to you to contact Orange first, they should be able to supply exact replacement pot.. ;)

Cheers thom for the info, i have just repaired i think? the pot but we have another problem now, i think one of the el84's has gone but i cant work out which one? if i put only one in nothing happens but when i change it to the other (also on its own) it starts to smoke one of the 470 ohm 5 watt resistors i think these two (one for each valve) connected in series are the screen? one tests now only 360 ohms could this be the cause for the smoking of this resistor? or is the valve gone? and the other valve which does nothing is good or what? i dunno i am confused? help!!!! please or anyone, cheers stavo.

[Blue Rock]

Hi, I´m new here and think this forum is very interesting.

I changed valves on the TT to get the sound I wanted and finally came up with this: gain 12AU7 (Sino), PI 12AT7 (Sino). This combination took away the gain I never use anyway, I max out the gain knob and get a much smoother overdrive.
Now I can also max out the tone knob without sounding harsh. The amp reacts much better to SC and sounds great with HB. I also use an EQ to take away some bass and a booster to crank it some more if I want to, and it still sounds smooth. My TT is Korean made and hooked up to the Orange 1x12 that came with it. A great little amp/cabinet combo!

[Blue Rock]

With 12AX7 at PI it's even better, less compression and more attack, still with smooth overdrive. Gain at 2-3 o'clock, tone at max, volume 10 o'clock (15 W setting).
This is a Terror I like!

[strangebru]

so, has anyone tried to mod the tone circuit to brighten the mid/hi response? great amp, but a really foggy tone and not much authority in the tone circuit
Cheers
mak

I was wondering the same thing, but I didn't see an answer here. Can the TT tone be permanently brightened without adding a full tone circuit. I am assuming that the tone circuit passes all high freq when full up, but is there a cap that can be changed somewhere that would help?

[John G]

Hi,
Try removing the cap off the second gain stage or reducing its value. The schem shows it as a 4.7nF cap which will bypass alot of the highs.
Try also shifting the position of the tone cut control from the wipers of the master volume control to the input side of the control, much more activity.
I can send you a schem of my TT clone and modifications if you want, just PM me.
Cheers,
John G

[Thomeeque]

The schem shows it as a 4.7nF cap

Which schem? AdmiralB's OTT.pdf shows 470pF..

[John G]

Hi,
The value I got was from a pdf circuit that was based on the Admrial's and is definetly a .0047uF. (C6)
I agree it should be a 470pF or none at all.
In looking at the whole schem I can't help wonder as to the acuracy of some of the component values given ?? As to the tone cut control in its present state it will only come into effect when the master control is used past about two thirds CW rotation.........I would think it was designed to work this way.
John G

[Thomeeque]

Hi,
The value I got was from a pdf circuit that was based on the Admrial's and is definetly a .0047uF. (C6)

There is probably more Admiral's TT schematics traveling around :) "Mine" does not contain part numbering (aka C6):
http://r.clear.home.insightbb.com/OTT.pdf Could you link "yours" pdf, please?


I agree it should be a 470pF or none at all.


I'll try both variants in my clone (when it's ready) - I'd expect this cap significantly influences final sound..


In looking at the whole schem I can't help wonder as to the acuracy of some of the component values given ?? As to the tone cut control in its present state it will only come into effect when the master control is used past about two thirds CW rotation.........I would think it was designed to work this way.
John G

I've seen already this setup in some other schematics (some old Marshall?), but I don't remember details..

T.

[strangebru]

There is probably more Admiral's TT schematics traveling around :) "Mine" does not contain part numbering (aka C6):
http://r.clear.home.insightbb.com/OTT.pdf Could you link "yours" pdf, please?

Because of the confusion on the value of this cap (and my nubeeness), I'm not sure which one we're talking about. On the, "Mine" schematic, can you describe where it is located. I see the 470pF cap (that T. mentioned) in parallel with a 100k resistor and both next to the D branch. Is that it?

[Thomeeque]

Because of the confusion on the value of this cap (and my nubeeness), I'm not sure which one we're talking about. On the, "Mine" schematic, can you describe where it is located. I see the 470pF cap (that T. mentioned) in parallel with a 100k resistor and both next to the D branch. Is that it?

Yes (or at least I am talking about this cap ;))

[sjwebb90]

Re:Admirals posting earlier on in the thread about bias.

I have measured the bias values on the EL84's of the Tiny Terror and it is indeed has a Plate dissipation of 15 Watts when in the 15W mode and is about 8Watts when in the 7Watt mode. Nominal Plate voltage for EL84's should be 12Watts.

Also to my ears the TT does sound a bit fizzy when distorted and the remedy appears to be, lower the 1.5 ohm resistor to 820 Ohms on the Phase Invertor, which I have done. For a more plexi crunch you could lower the value further to 470 Ohms. After trying both I stuck with the 820 Ohms. The fix also opens the amplifier up offering more clarity.

Cheers
SJ

[John G]

SJ,
In the schem I sent Thomas I have incorporated a DPDT toggle switch so that I can select the standard splitter tail resistor values and have these option of throwing the switch to shunt the tail resistors and lowering the resistor values to that of a Marshall ie 470 ohm, and 15K ( there is no feedback connection so no 10K,4K7 split) Makes a bit of a "plop" when you throw it on the fly but is not a Major.
You are right if you want better head room at this point then Marshall values are the way to go.
If you think the O/P tubes are over dissapated then up the cathode resistor in the Hi power mode and take it down(via the power select switch DPDT) for the lower power option as has been suggested in the thread ealier.
Cheers,
John

[sjwebb90]

John thanks for your reply.

Strangely, I was looking at the Cathode bias resistor "verses" plate discipation earlier in the day.

EL Teye observations on an earlier thread appear to have some foundation when "he" changed the Bias resistor to 180 Ohm
Quote "My amp lost punch, bite, and some volume in the 15Watt setting.

My test on 15W setting :
I placed a Rheostat in line with the 120ohm resistor so I could heard any difference on the fly. The amp was set to a clean sound.

With bias resistor set at 180 Ohm and the plate discipation measuring the nominal 12 Watts, there was definitley a lack of sparkle and the strings seemed a bit muted. Moving the rheostat back and forth between the setting
180ohm and 120 ohm you could hear a audible difference.

I am a bit puzzled with that at the moment, because if everything is running at optimum you would expect to get a better tone. Also with the Plate running at 15 watts in the 15W mode the valve life will be reduced which is a distinct negative.

Luckily at the moment I use it soley as a practice amp at the 7W setting.

Out of curiousity, has anyone else done any direct A/B testing on the fly of 120 verses 180 and detected any difference?

[Thomeeque]

As to the tone cut control in its present state it will only come into effect when the master control is used past about two thirds CW rotation.........I would think it was designed to work this way.
John G

Yesterday I've seen other OTT schematic, where "tone cut" control was first on signal path before "master volume" pots. I don't know if AdmiralB made mistake when drawing his schematics or if this is difference between OTT revisions.

[stavo]

Cheers thom for the info, i have just repaired i think? the pot but we have another problem now, i think one of the el84's has gone but i cant work out which one? if i put only one in nothing happens but when i change it to the other (also on its own) it starts to smoke one of the 470 ohm 5 watt resistors i think these two (one for each valve) connected in series are the screen? one tests now only 360 ohms could this be the cause for the smoking of this resistor? or is the valve gone? and the other valve which does nothing is good or what? i dunno i am confused? help!!!! please or anyone, cheers stavo.

No worry's guys i have fixed the little bastard!!! Now to build my own 20 watter!

[Blue Rock]

Tried pulling the bright cap, to cut some of the high end (so subjective, and other people want MORE upper mids?!?!?)
:D

Hi! Where do you mean "the bright cap" is located?

[Blue Rock]

gain 12AU7 (Sino), PI 12AT7 (Sino).

Sorry, I mixed up the two valves... 1:st valve (gain) 12AT7 and 2:nd PI 12AU7.

[Blue Rock]

With 12AX7 at PI it's even better, less compression and more attack, still with smooth overdrive. Gain at 2-3 o'clock, tone at max, volume 10 o'clock (15 W setting).
This is a Terror I like!

Mixed up the valve positions so the above mentioned is the 12AX7 as 1:st valve and 12AU7 as PI.

[Thomeeque]

Hi! Where do you mean "the bright cap" is located?

IMO there's only one, which could be called "the bright cap" and it's 100pF cap on first gain pot.. for low gain setting it will have probably significant influence.. T.

[strangebru]

IMO there's only one, which could be called "the bright cap" and it's 100pF cap on first gain pot.. for low gain setting it will have probably significant influence.. T.

So could this 100pF "bright cap" be changed (raised I guess) to go in the opposite direction to make sound even brighter?

Or is the previously discussed 470pF cap the better one to change to make sound brighter? Did we ever fully establish that this was the cap that John G was talking about when he said "Try removing the cap off the second gain stage or reducing its value."?

[Thomeeque]

So could this 100pF "bright cap" be changed (raised I guess) to go in the opposite direction to make sound even brighter?

I'd say no - by increasing it's capacity you would just lower the frequency, where boost starts.

Or is the previously discussed 470pF cap the better one to change to make sound brighter?

Yes, I'd start here..

Or you can try to add "bright cap" to second gain pot! :)

Or do both. :)

And you can try to add "bright cap" to master volume pots as well btw. (but keep it symmetrical) ;)

Or in parallel with one or both of 68kohm resistors (and maybe increase those resistors value to - lets say - 220kohm..?)

There lot of room to play, but be prepared, that you can get into oscillations if you gain it to much..

Enjoy! :)

Did we ever fully establish that this was the cap that John G was talking about when he said "Try removing the cap off the second gain stage or reducing its value."?

Probably not, but I can establish that now ;) - John has sent me his schematics via e-mail meanwhile, and it's obvious.

T.

[John G]

Hi,
Just thought I would clarify that the Schem of the TT I found on the net has the second gain stage anode resistor with a 4n7F cap across it. It has been pointed out that that schem in incorrect and it is in fact a 470pF. Removing this cap will improve upper brightness.
The cap across the volume control bleeds high frequencies but is dependant on the setting of the control ie with control down (ccw)more frquencies will be passed compared to when the volume is fully maxed (cw) then the cap is shorted out so will have no effect. This arrangment is usefull when you lower the volume you get a lift in treble, like the brite switch on a Fender amp.
I hope this clears things up.
John G

[strangebru]

Hi,
Just thought I would clarify that the Schem of the TT I found on the net has the second gain stage anode resistor with a 4n7F cap across it. It has been pointed out that that schem in incorrect and it is in fact a 470pF. Removing this cap will improve upper brightness.
The cap across the volume control bleeds high frequencies but is dependant on the setting of the control ie with control down (ccw)more frquencies will be passed compared to when the volume is fully maxed (cw) then the cap is shorted out so will have no effect. This arrangment is usefull when you lower the volume you get a lift in treble, like the brite switch on a Fender amp.
I hope this clears things up.
John G

Is that 470pF cap just for tone shaping or is it also for controlling oscillations, maybe unaudible oscillations that can only be seen on a scope? Have you tried removing it in your amp? If it does help control oscillations, what value do you think would be good if I just wanted a little more bright but didn't want to risk oscilations?

[John G]

Hi,
To answer your questions, yes and yes ! Try reducing the value to say 100pF, on my clone I dispenced with it all together. Yours may behave differently, try it and see.
John G

[MFTech]

Ask and ye shall... (http://r.clear.home.insightbb.com/OTT.pdf)

FYI: I drew out the schematic on an earlier Korea Tiny Terror some time ago. It seems there are a couple differences from Admiral's schem... although, I might have made an error... any other drawers out there to confirm?

1) Coupling cap C15 into PI is .0022uF on mine (.047uf on Admirals)
2) Tone control circuit is located right after master volume rather than after PI. (C13 cap is .047uF rather than .0022uf)
3) R19 is 100K (connected to V2 plate) rather than 68K

All else is the same... as I said, it's probably my mistake. Not the easiest layout to trace being a dual sided PCB.

P.S. The guys at Mercury Magnetics are working on a Tiny Terror tranny upgrade kit like the Epi Jr kit. They made it sound like it was going to be absolutely killer... I plan to use the kit to build a PTP version of the TT from scratch. Although, nothing wrong with the stock TT!

[Thomeeque]

FYI: I drew out the schematic on an earlier Korea Tiny Terror some time ago. It seems there are a couple differences from Admiral's schem... although, I might have made an error... any other drawers out there to confirm?

1) Coupling cap C15 into PI is .0022uF on mine (.047uf on Admirals)
2) Tone control circuit is located right after master volume rather than after PI. (C13 cap is .047uF rather than .0022uf)
3) R19 is 100K (connected to V2 plate) rather than 68K

All else is the same... as I said, it's probably my mistake. Not the easiest layout to trace being a dual sided PCB.

P.S. The guys at Mercury Magnetics are working on a Tiny Terror tranny upgrade kit like the Epi Jr kit. They made it sound like it was going to be absolutely killer... I plan to use the kit to build a PTP version of the TT from scratch. Although, nothing wrong with the stock TT!

Hi!

Would you mind to share your schem (even you think there are errors)? Btw. I know that mathia (http://music-electronics-forum.com/showthread.php?p=52258#post52258) has drawn schem (or at least fragments) out of his OTT unit circuitry, maybe he would not mind to share it either (he has found some differences too btw.).

T.

[MFTech]

Hi!

Would you mind to share your schem (even you think there are errors)? Btw. I know that mathia (http://music-electronics-forum.com/showthread.php?p=52258#post52258) has drawn schem (or at least fragments) out of his OTT unit circuitry, maybe he would not mind to share it either (he has found some differences too btw.).

T.

UPDATE: I doubled checked the TT & I did have a couple errors on my schematic. Everything on Admiral's schematic appears to be correct with the exception of R19. (resistor following V2 stage) It is 100K in my chassis rather than 68K as on his schematic.

[John G]

Hi,
A amp tech mate of mine had a TT on the bench briefly, only had a very short time to look as customer was waiting.
He did confirm thet the 68k was in fact 100k and all rest seems to be accurate as per the Admirals schem, except the the Master Volume was marked on the pcb as 100k log ???, unfortunately he had no time to measure.
With the 0.1uF caps feeding the M/V then maybe the 100k is correct. ie a better low frequency roll off point.
Any coments.
John G

[MFTech]

Hi,
all rest seems to be accurate as per the Admirals schem, except the the Master Volume was marked on the pcb as 100k log ???, John G

For pots, I have:

GAIN: 500KA dual
TONE: 500KB
MASTER: 100KA dual

[MFTech]

Here is an updated TT schem that has voltages, some part locations, & couple component value corrections.

here ya go... (http://russosmusic.20m.com/TT15.jpg)

[John G]

Hi ,
Thanks for the update, much appreciated.
PS there is an 4A PC mount fuse in the heater line.
John G

[Thomeeque]

Btw. YouTube - Tiny Terror Jule Mod (http://www.youtube.com/watch?v=gpzwU5QfV4w)

It could be maybe useful to invite Jule here ;)

T.

Edit: At http://www.juleamps.com/ you can download same video in better quality (WMV format). When stepping frame by frame you can even see bit of what's going on ;)

[sjwebb90]

One thing that is most noticable from the Jules mod is that he has added a transformer.

Anyone any thought as to whats going on here. I suspect it maybe a replacement for the output transformer?

I have an early Made in Korea variant and regarding EL84 carthode bias it is as admiral has stated are not running to what would be deemed the correct spec.

Measurements on my unit (ignoring screen current)
15Watt
120 Ohm resistor = 15Watts on the Plate of the valve
120 Ohm resitor = 8 Watts on the Plate of the Valve

Obviuosly if you run on the 15 Watt setting the Valve life will be greatly deduced.

With Modified Biasing
15Watt mode
180 Ohm resistor Plate Voltage 346V Cathode Voltage 12.6V
Bias Current 12.6v/180 =0.070mA 0.070mA/2 = 0.035mA per valve

Power =346-12.6 x 0.035 = 11.7Watts

7 Watt Mode 180 Ohm in parrallel with 100 Ohm
64 Ohms Plate Voltage 238V Cathode Voltage 6.1V
Bias Current 6.1V/64 Ohms = 0.095mA 0.095mA/2 =0.047mA per Valve

Power =238V-6.1 x 0.047 =11 Watts

On my TT Biasing the amp correctly gets rid of surplus fizziness when used with distortion and it sounds fuller on both settings.

However, what you seem do loose when playing Clean is a bit brightness and twang.

Out of curiousity could someone have a look, if they have one, of Made in China variant with the 120 Ohm resitor fitted and see what the biasing is set too, because someone has pointed out the switching is different too (Standby Switch).

Also does anyone know what orange has added the .22uf capacitor at the input, not something you norammly see at the input of a valve amp

Cheers
SJ

[Thomeeque]

One thing that is most noticable from the Jules mod is that he has added a transformer.

Anyone any thought as to whats going on here. I suspect it maybe a replacement for the output transformer?

It's most probably choking coil for additional power-supply filtering - when stepping WMV video you can see only two wires going out of this "transformer".. he even states this in one youtube comment:

"This mod is a lot like the mods done to the early VOX AC15s and VOX AC30s. As with those mods, we focus on cleaning up the power supply both on the output section and the preamp. There is inductance added to bring out some musicality. And some other things. I've also found some enhancements to several manufacturing issues."

[strangebru]

I just replaced the 100pf "bright cap" with a 470pf cap. It made the clean (gain between 9 & 12 o'clock) sound more bright and alive. And it has more brightness all the way up to 2 o'clock. I found that with the spec 100pf cap it was way to muffled in this clean region. I was really dissapointed with this aspect of the TT. So this change did exactly what I wanted. If I need less brightness for some reason, I can always turn the tone knob down. I'm really pleased with the results.

I arrived at the 470pf value by experimenting incrementally using alligator clips and putting more and more 120pf caps in parallel while the gain was at about 11:00. Each time I added a cap in parallel the high end became more alive. I also continuously checked the results to make sure that I wasn't sending all the frequencies thru the caps (thereby defeating my purpose). I did this by shorting out all of the caps, which made the gain go up on all the frequencies, giving a louder but muffled sound like before. This showed me that I still had room for more caps. When I used many more than three caps (5 or 6) the sound began to be just louder but not brighter, approching the shorted out sound. So, I stopped at three 120pf caps added, which makes 460pf in total. Pulled out the 100pf cap and replaced with 470pf cap. I guess the 100pf cap they had in there was just not sending enough higher frequencies when the gain was low for my taste. To my ears, the TT at full up on tone, now sounds much like the clean channel of my JCM600 Marshall at full treble, which has a very nice clean bright (but not too bright or harsh) sound. That's what I tried to match.

[strangebru]

Although I just got it a few weeks ago, my TT says "made in PRC" on the box and board, on April 6 2007. I looked at the tubes and there is no markings on them at all !!! Does anybody know who makes these things ? Are they the JJ's in disguise?

[Thomeeque]

Although I just got it a few weeks ago, my TT says "made in PRC" on the box and board, on April 6 2007. I looked at the tubes and there is no markings on them at all !!! Does anybody know who makes these things ? Are they the JJ's in disguise?

China already makes tubes, so I'd guess they use Chinese tubes there, they are cheapest and not bad. Price is around 70% of JJ's in the shop (http://www.ges.cz/?ipp=12&lang=en&cur=EUR&or=price,asc&page=index&of=1&gcat=XRC_A&inc=browse) where I buy stuff .. OK, now this shop does not sell them anymore, interesting.. I have bought there two Chinese 12AX7's before six months to save some money and to try them and they are good so far! Hmm, I'll ask them occasionally.

Btw. even SOVTEK (Russian) tubes are cheaper than JJ's, so I'd be surprised if it was JJ's (JJ's would be probably marked properly, no reason to hide it - or is there something I don't know? :))..

[sjwebb90]

Just been taking a look at the Mercury Magnetics site and due June 08 is a transformer upgrade kit for the TT. No sign of a choke in that upgrade. I suspect they are probably addressing the biasing issues as well.

http://www.mercurymagnetics.com/pages/catalog/kits/TinyTerror/Orange-TT.htm.

With regards the choke in the PSU of older Vox amps, I am led to believe that the choke was there because the amps weren't using full wave rectification, they were just using two diodes / rectifier valve and the power rails were thus a bit ropey so they added the choke to the circuit.

As the modern designs have full wave rectification and good power rail smoothing then why do you really need to add a choke?

SJ

[Steve A.]

I just replaced the 100pf "bright cap" with a 470pf cap. It made the clean (gain between 9 & 12 o'clock) sound more bright and alive. And it has more brightness all the way up to 2 o'clock. I found that with the spec 100pf cap it was way to muffled in this clean region. I was really dissapointed with this aspect of the TT. So this change did exactly what I wanted. If I need less brightness for some reason, I can always turn the tone knob down. I'm really pleased with the results.

I arrived at the 470pf value by experimenting incrementally using alligator clips and putting more and more 120pf caps in parallel while the gain was at about 11:00. Each time I added a cap in parallel the high end became more alive. I also continuously checked the results to make sure that I wasn't sending all the frequencies thru the caps (thereby defeating my purpose). I did this by shorting out all of the caps, which made the gain go up on all the frequencies, giving a louder but muffled sound like before. This showed me that I still had room for more caps. When I used many more than three caps (5 or 6) the sound began to be just louder but not brighter, approching the shorted out sound. So, I stopped at three 120pf caps added, which makes 460pf in total. Pulled out the 100pf cap and replaced with 470pf cap. I guess the 100pf cap they had in there was just not sending enough higher frequencies when the gain was low for my taste. To my ears, the TT at full up on tone, now sounds much like the clean channel of my JCM600 Marshall at full treble, which has a very nice clean bright (but not too bright or harsh) sound. That's what I tried to match.

That sounds like a good idea when I think back at the TT I tried out in the music store- maybe it was the cabinet but I did think that the clean sounds were a bit muddy. Perhaps adding a switch to select values for the bright cap might be a good idea, too.

[strangebru]

That sounds like a good idea when I think back at the TT I tried out in the music store- maybe it was the cabinet but I did think that the clean sounds were a bit muddy. Perhaps adding a switch to select values for the bright cap might be a good idea, too.

You probably don't need the switch because you can always turn the tone dial down to unbrighten or muddy it up.

BTW, this thing sounds great now. Someone on harmony central (user music review) said TT is too dark, forget the Byrds "Turn, Turn, Turn" or anything like that. Well now it can do it with flying colors. Before, the most treble guitar there is, my rickenbacker 12 string, even sounded dull (imagine that). Now it shimmers and chimes just like its suppose to.

[Steve A.]

You probably don't need the switch because you can always turn the tone dial down to unbrighten or muddy it up.

BTW, this thing sounds great now. Someone on harmony central (user music review) said TT is too dark, forget the Byrds "Turn, Turn, Turn" or anything like that. Well now it can do it with flying colors. Before, the most treble guitar there is, my rickenbacker 12 string, even sounded dull (imagine that). Now it shimmers and chimes just like its suppose to.


Well, Trainwreck Express amps usually had a 3 position swich for the bright cap: 100pF, 500pF or none at all. Funny thing with that design in clones- I could hear the difference in bright caps with the volume control dimed (although theoretically it should be shunted out of the circuit).

On a real Orange chassis you might not want to drill another hole for a bright switch but on a clone chassis it is a very tempting idea. And it would give you more tone options (adjusting the tone control would have an effect regardless of the setting of the initial gain controls).

Thanks

Steve Ahola

[John G]

Steve,
You hit the nail on the head there, keep the TT for Sunday best (ie keep its value ) and cobble up a clone, you will always have the reference to compare with, and you can learn and enjoy the art of tinkering and hear what differeces changes can make.
I must say as a tech all my home brews would look similar to yours Steve I suspect, there are more switches on mine that a 747 fleight console, hell you don't even need to play the guitar you can have so much fun just throwing switches.
My TT clone has seperate passive bass (pre)and assignable treble control (pre or post), PP/SE switch,Pentode/Triode switch.........
You get the picture.
Oh! by the way Steve it was you who got me into this Amp modding Junky obesssion............Thanks
John G

[OverDriven]

Hi guys...this is my first post. My name is Joe and I've been playing guitar for 10 years now. I've looking into amp building in the past, but now I would like to get serious about it and actually go for it. I have some electronics experience and I'm a very logical person with a good ability to pick up things like this fairly quickly. I'm building my very first amplifier and really like the sound and simplicity of the TT. What I would like to do is mate the TT preamp section with a 50 watt (2xEL34) power section. How difficult is this going to be for a beginner to amplifier building? How much is changed from the original schematic? What power and output transformers (I would like to use Hammond for this first build) would you recommend? Thank you for any info!

[Thomeeque]

What I would like to do is mate the TT preamp section with a 50 watt (2xEL34) power section. How difficult is this going to be for a beginner to amplifier building? How much is changed from the original schematic? What power and output transformers (I would like to use Hammond for this first build) would you recommend? Thank you for any info!

Hey Joe, Welcome! :)

AFAIK you can keep circuit as it is and get approx. 40 Watts using EL34's instead of EL84's (for full 50 Watts you would have to create different biasing circuitry). Source voltage has to be gained to approx. 400V and both transformers have to be dimensioned relevantly. And here my knowledge ends, at least for now (I have some reading about this, but it's in Czech, I have to study it for a while).

Btw. another possibility is to add another pair of EL84's, you get 30-40 Watts this way.

Tomas

[sjwebb90]

Re a previous posting reference the biasing of the TT. This time factored in the Screen current. However,due the to the TT being PCB mount I decided not to mess about measuring it, but for all intents and purposes the screen current can be seen as approx 10% of the cathode current. Ideally I should have factored this in last time, because however small, does have a bearing on the calculations.

EL84 valves fitted are factory fitted JJ Tesla. Unit is an early Made in Korea example.

I have since replaced the 180 Ohm resistor for a 150 Ohm. (Actual reading of resistor was 147 Ohms, slightly under reading).Calulations are as follows :

15Watt mode
150 Ohm resistor Plate Voltage 336V Cathode Voltage 11.60V

Bias Current 11.60v/147 =0.079mA
0.079mA/2 = 0.0395mA per valve.

Taking screen current to be 10% of Bias current = 0.003ma Approx

Therefore 0.0395 - 0.003 = 0.0365mA

Plate Voltage - Cathode Voltage = 336 - 11.60 = 324.32V

Plate discipation = 324.32 x 0.0365 = 11.8Watts

7 Watt Mode 147 Ohm in parrallel with 100 Ohm
59 Ohms Plate Voltage 237V Cathode Voltage 5.82V

Bias Current 5.82V/59 Ohms = 0.0986mA
0.0986mA/2 =0.0493mA per Valve

Taking screen current to be 10% of Bias current = 0.004ma Approx

Therfore 0.0493 - 0.004 = 0.0453mA

Plate Voltage - Cathode Voltage = 237 - 5.82 =231.18V

Plate discipation = 231.18 x 0.0453 =10.5 Watts

On my particular unit, with the 180 Ohm resistor fitted the unit was running a bit "cold" and was accounting for the lack of sparkle. There is now a little more volume.

In the 7 Watt mode the Cathode bias resistor could ideally be a little lower to lift the plate discipation (perhaps 50 Ohms). I may have a fiddle with that again but at present things are sounding OK and I will probably leave alone.

Biasing between 10.5 Watts and 11.5 Watts is generally regarded as being OK.

[sjwebb90]

I have taken a couple of photo's to show the placement of resistors with regards the re-biasing should anyone be interested.

http://www.flickr.com/photos/66957213@N00/2627824665/

http://www.flickr.com/photos/66957213@N00/2627824975/

http://www.flickr.com/photos/66957213@N00/2628642862/

[Alex/Tubewonder]

Your current calculations are off by a factor of 1000 ;)
It's amper?s not miliamper?s....

[sjwebb90]

Alex, thanks for pointing out the faux par..must have been having a senior moment.

I had dropped in references to mA instead of A in certain parts of the equations, where there shouldn't be.

i.e (0.0395mA) should have read 0.0395A or 39.5mA

Please note the results are actually correct with regards the Plate wattage as shown, its was just committing the calculation process to the article that was in error.

Apoligies for any confusion.

[Thomeeque]

Hey, guys! So, how's your clonning going? :)

I have finished chassis+electronic part of mine clone before a while, and after some tweaking I'm really happy with the actual results (even it's not perfect yet and I still have some tweaks on schedule)..

http://thmq.mysteria.cz/pidilampac/thumb/cute15.jpg

(click to see whole genessis, hot&sexy details and preamp schematics) (http://thmq.mysteria.cz/pidilampac)

As you can see, it's not 1:1 clone (there's DC for ECC83 filaments, switchable 2-band EQ, Sensitivity and Boost switch, direct PA input, two simple Gain pots instead dual one and TT/Marshall PI mode switch), I have wanted more versatile amp, but it's still switchable to almost 1:1 TT circuitry (and honestly this mode /with Marshall PI mode/ so far rules :D).

So what you say? :)

Btw. DIODES switch = PI mode switch ;) I have decided to change my original idea, when labels were done and placed already :)

And I still have to design and order top and bottom covers.

[Alex/Tubewonder]

Excellent job on metal work and transformers. OT with label listing winding details, cool old school touch. Really, really nice.

Now to a couple questionable points:

*how is the sub panel with pots and switches grounded?

**PSU board: I'm a bit worried the isolation distances between tracks are to small and you may get arcing there.

***Boost switching arrangement can be a source for loud pops. It's better to have a large resistor in series with each cap and short the resistor for boost function.

Who does your chassis? I might have a job for them. Please PM me with info.

[Thomeeque]

Hmm, thanks for your quick and wistful answer!

Excellent job on metal workyep, I love it too, done by real pro (more in PM)

..and transformers. OT with label listing winding details, cool old school touch.both transformers were ordered from TRONIC (http://www.trafo.cz/en/).

*how is the sub panel with pots and switches grounded?subpanel has conductive connection with main chassis (which is grounded to wall) - but only by screws, not wired, bad idea? Is it about security? Btw. pots are plastic, only back covers are metallic, they are all connected and grounded by one wire to PA ground (on Volume pots)

**PSU board: I'm a bit worried the isolation distances between tracks are to small and you may get arcing there.yes, especialy those psychedelic shielding swirls were probably stupid idea (it even crossed my mind when drawing PCB if there should not be more space between tracks, but I've seen gutshots of EH Black Finger and they have even smaller distances between high voltage tracks and ground).. OK, so far I have not any problem with arcing - should I still worry? Can this get worse? Is there something I can do to avoid it with current PCB (isolating varnish?)?

***Boost switching arrangement can be a source for loud pops. It's better to have a large resistor in series with each cap and short the resistor for boost function.OK, in this case I knew exactly what I'm doing, I have just decided to try it without those resistors for simplicity reasons (it's very tight area around this switch and it would be 4 more resistors there). I don't thing I will switch often later, and even up to now I have not registered any annoying pop.

[GainFreak]

Hi,

I just built my clone.
In 15W mode anode voltage is 330V, cathode bias resistor 120 Ohms. Bias voltage is 10.3V which means ~12.9W plate dissipation /grid current is ~4mA and is subtracted from calculations/.
In 7W mode I'm adding /via DPDT switch/ a 630 Ohm resistor in series with the HV tap and another 120 Ohm resistor in parallel. Anode voltage is 254V, bias voltage is 6.1V which means ~11.9W plate dissipation.
Things that I noticed. There's no difference in volume levels between 15 and 7W mode. In 7W mode the tone changes but only a bit - nothing drastic.
When gain is past 3 o'clock and Master is at max I'm getting a noise which sounds like a ground loop noise. When gain is at max but Master is around 3 o'clock the noise is almost inaudible. Tried several grounding points but it's still there. Maybe this beast has too much gain and filament hum leaks into the amplified signal?
I would appreciate if you have any ideas how to solve this.
Filaments are AC, dual pots are 1M with different value resistors across them in order to match the original ones. Everything is PCB mount.

[strangebru]

I think I may have blown the power transformer on my TT. After playing guitar directly plugged in at moderate volume for about 20 minutes, it started sounding about half as loud somewhat suddenly. Then it came back to normal after I removed and replugged in the speaker wire. Then it began to fade again. I shut it off waited and turned it on and it came back to normal again. Then after a minute it faded again, and then faded out completely.

There was no burning smell or smoking from amp.

Now at this time, I have to mention that I had done a very bad thing. I had another amp (the all tube 5 watt Blackeart with a 16 ohm speaker output) plugged into (with power off) the same 16 ohm 1x12 cab that the TT was plugged into. Thereby probably putting the Blackeart speaker transformer output in parallel with the TT output. I check the resistance of this combination with an ohm meter and it read around 12 ohms. I also checked the resistance of just the Blackheart output and that was about the same !?!?

I openned up the TT and turned it on to see if the tubes were glowing because I thought at 1st maybe it was the tubes. It worked for a minute or so and then faded again. The tubes initailly glowed then the power tubes faded to dark. The preamp tubes still glow even when sound is completely gone and power tubes are dark.

I replaced both power tubes, nothing changed. Put old ones back.

Waited several hours, no sound at all, power tubes dark, preamp tubes glow.

So do you think it is a capacitor in the power supply chain or a section of the transformer that supplies the "glow"?

Next I will try to measure the Xformer voltages I guess. Do the filiments glow with AC directly from Xformer?

Please help if you have any insight into this unfortunate occurrence !!!

Thanks,
Bruce

[strangebru]

I checked the transformer. It gets what it says it should on the secondarys.

I checked the supplies to the tubes: the power tubes get about 320 VDC on 2 pins each, the preamp tubes are getting around 220-250 VDC; and the filaments (I guess) are getting about 6 VAC on all tubes. So I guess the transformer is OK.

I tried the amp again and it worked for a minute or so then died again. I measured the voltages and they were the same as stated above. The power tubes are dark and cold even though they have 320 VDC on them and they are getting 6 VAC. How can that be ?

What does this mean ???

Is that PC board fuse a thermal fuse that's malfunctioning?

I turned amp on full blast and strummed chords (of course there was no sound, because its not working) and measured the voltage on pin 2 (unless I got it backwards, then maybe pin 8) of both power tubes and got about 40VAC on each. With no strumming the voltage is 0.0. But nothing from the speakers. I measured the output of the output xformer under these same (guitar strumming) conditions, and no AC voltage was present. So I guess that this means that the output xformer is shot. Does that sound correct? Is there another test that would prove this outside of buying a new one?

[Thomeeque]

So I guess that this means that the output xformer is shot. Does that sound correct? Is there another test that would prove this outside of buying a new one?

Hi!

If there is something wrong with filaments on power tubes (power tubes dark), this can be source of whole problem and you should focus on that at first place!

Now, filaments are powered directly from PT, no capacitor is involved in this problem.

Fuse is not probably involved either, beacuse it's one for all filaments (so even preamp tubes would have to be dark). Plus it's simple fuse - when it burns once, it's burned for good, no way it could recovery..

What can be involved further depends on where exactly did you measured the filaments voltage! Was it on PCB directly on V3 and V4 pins (pin 5 and 4)? If yes, there maybe something wrong with soldering of these pins (try to resolder) or with pins inside socked (it can be rusty for example, try to clean it somehow). If not, measure it directly on V3/V4 pins 4 and 5 first.

If the voltage is not there, check whole path from V3/V4 pins to PT. I would not be surprised if the problem was in bad connection in one of filaments power connectors on PCB (rusty or burnt pins), where twisted black and yellow wires go (these wires distribute current for filaments to all valves - see sjwebb90's pics 1 (http://www.flickr.com/photos/66957213@N00/2627824665/), 2 (http://www.flickr.com/photos/66957213@N00/2627824975/), 3 (http://www.flickr.com/photos/66957213@N00/2628642862/))

I'll continue later..

[Thomeeque]

Is there another test that would prove this outside of buying a new one?

To make simple "global" test of OT you can do following:

- remove power cord from amp
- pull out both power tubes
- plug in speaker (but unplug second amp!! ;))
- get some small voltage source (e.g. 1.5 Volt battery)
- connect one pole of battery to pin 7 of V3
- touch by second pole of battery pin 7 of V4
- this way you will generate pulse into OT
- you should here pops from speaker by each pulse

Of course, be careful, double-check there's no dangerous voltage on any part you are planning to touch (e.g. pins 7)!

[strangebru]

Well, I checked the filament voltages as noted in my post, they are all about 6 VAC. Also, as in my SOS post prior to this I replaced the power tubes, same symtoms. This is a brand new amp, no rust. If you disconnect the wire to you speaker (I know this is not good for more than a few seconds) do your power tubes still light up? I say this, because if the secondary of output xformer is shot, then this would be a similar situation, in that no current goes thru secondary. Therefore no current thru primary, yes? Therefore, tube is doing no work, so its cold?

[strangebru]

OK, I will try this, but just a couple of things. Pinout question: how are the pins numbered? Is it clockwise looking down from top, or counter clockwise, or is the convention from loking at the bottom? Also, could I not do this same check by putting battery right on to the primary leads?

[Thomeeque]

Well, I checked the filament voltages as noted in my post, they are all about 6 VAC. Also, as in my SOS post prior to this I replaced the power tubes, same symtoms. This is a brand new amp, no rust. If you disconnect the wire to you speaker (I know this is not good for more than a few seconds) do your power tubes still light up? I say this, because if the secondary of output xformer is shot, then this would be a similar situation, in that no current goes thru secondary. Therefore no current thru primary, yes? Therefore, tube is doing no work, so its cold?

As far as I know glowing of tubes depends only on filaments voltage. Current status of output transfromer (and rest of circuit) has no influence on this! Believe me, if the power tube is dark and cold, there's no voltage on it's filament, period. And because you have tried other pair of tubes with same results, you should check amp. There can be for example cold-soldered joint even on brand new amp or some defect in sockets etc.

[Thomeeque]

OK, I will try this, but just a couple of things. Pinout question: how are the pins numbered? Is it clockwise looking down from top, or counter clockwise, or is the convention from loking at the bottom?

http://tdsl.duncanamps.com/basing/b9a.gif

(bottom view, e.g. as you see it on PCB from soldering side)

Also, could I not do this same check by putting battery right on to the primary leads?

Yes (that's the point, but I didn't know that it's accessible for you - I don't own original OTT, just my humble clone ;))

[strangebru]

OK. It does make a sound.

News flash: You may have been right with your cold solder theory. Its all a little strange though. I measured these filament voltages at 6 VAC right at the tube pins and get 6 VAC. Yet there IS a very bad cold solder on the supply clip to the power tubes. When I press down the amp light up. Well I will fix it right now. Even though it doesn't completely make sense. I'll keep you posted. Thanks.

[strangebru]

I removed the board and looked at the underside solder job. Very poor on ALL of the filament clips. They were all loose. I could see the metal posts moving inside of the cold solder. Difficult to fix some of them because they were in the middle of the tube mount assembly. But I managed to get enough heat and solder in there to help them.

Its been working for at least 20 minutes now. I guess that was it.

Thanks a lot for your help Thomeeque.

Now to play guitar, I think that's what these things are for ;)

[GainFreak]

Do your TT amps produce any other noise/hum when gain is past 2-3 o'clock than the usual hiss?
On my clone when gain is past 3 o'clock and Master is at max I'm getting a noise which sounds like a ground loop noise. When gain is at max but Master is around 3 o'clock the noise is almost inaudible. Tried several grounding points but it's still there. Maybe this beast has too much gain and filament hum leaks into the amplified signal?
I would appreciate any help.

[strangebru]

Do your TT amps produce any other noise/hum when gain is past 2-3 o'clock than the usual hiss?
On my clone when gain is past 3 o'clock and Master is at max I'm getting a noise which sounds like a ground loop noise. When gain is at max but Master is around 3 o'clock the noise is almost inaudible. Tried several grounding points but it's still there. Maybe this beast has too much gain and filament hum leaks into the amplified signal?
I would appreciate any help.

With nothing plugged in, up full, no sound at all. With guitar cord plugged in but guitar volume off, there IS some hum (hiss is a slightly louder than hum) as gain and/or volume begin to approach their max's together, doesn't matter which is max'd 1st. The hiss, of course, is very loud. With guitar volume on, at those volumes, just containing the feedback is impossible, even with guitar strings muted by being upside down on carpet at 15 ft away (to the side). Hope that helps.

[GainFreak]

With nothing plugged in, up full, no sound at all.

Yes, I was talking when nothing is plugged in. When playing this noise is unnoticeable.
I thought the OT is coupling to the PT because they're close but moving it around didn't help.

[strangebru]

Yes, I was talking when nothing is plugged in. When playing this noise is unnoticeable.
I thought the OT is coupling to the PT because they're close but moving it around didn't help.

I mean completely absolutely silent, as in probably the speaker is cut off when the input is not plugged in.

[Thomeeque]

Do your TT amps produce any other noise/hum when gain is past 2-3 o'clock than the usual hiss?

I had two such problems with my clone:

1st was "dirty" noise with randomly varying intensity caused by problematic V1 tube (12AX7 by EHX), it vanished after replacing this tube.

2nd was oscillations around 20kHz (not audible of course, but it caused huge current consumption leading to intensive 100Hz hum plus I was not able to make amp loud), caused by coupling between OT and input circuit (most sensitive was input capacitor /twisted foil 220nF/) - it vanished after adding OT shield.

Could you record and put here sample of your noise (because at least I don't know how "ground loop noise" sounds ;)), maybe it will ring some bells :)

T.

[GainFreak]

It turned out to be the power transformer which was very close to the tubes and was causing this noise. It was a toroidal PT- obviously they're not so quiet when they are 1 inch close to the tubes.
Thanks for your help.

[Thomeeque]

I removed the board and looked at the underside solder job. Very poor on ALL of the filament clips. They were all loose. I could see the metal posts moving inside of the cold solder.

Scary!

Its been working for at least 20 minutes now. I guess that was it.

Good! If it should happen again, I would advice you to bypass these clips by soldering wires directly to tube socket pins on PCB..

Thanks a lot for your help Thomeeque.

You are welcome! :)

Now to play guitar, I think that's what these things are for ;)

Definitely! :D

[iWishmaster]

Hi everybody,

This is my first post on this forum. I'm planning on making an amp based on the TT. I'm an electrical engineer, but I've never worked with tubes, so some I'm kinda new to this stuff.

I figured out how the thing works by analizing the schematic (thanks a lot for posting it btw Admiral!). I'm planning on making some changes to it:
-Removing the 7/15W switch (where am I gonna find a PT that has seperate taps like that anyway ...)
-Adding a bright switch as some people suggested, by switching the treble 'bleed' C between 100 and 470pF on the first gain pot. (Can anyone confirm if it is a little cleaner at high volumes with a higher C value?)
-(later, when the amp is finished): Adding a (footswitchable) equalizer based on an EQ pedal or graphic EQ, such as found in the Mesa Mark IV between the preamp and poweramp.
-(later, when the amp is finished): Messing around with it, maybe changing some other stuff depening whether I like the tone enough or not.

My problems:

Number 1:
Selecting a suitable OT. Does anyone know what the Load Resistance of the two EL84's is at 325V plate? The datasheets only specify R(L) at 5.2kOhm, with 250V plate in Class A.

Number 2:
The pins on the EL84's. I tried figuring it out, but I'm sure if I'm right, please correct me if I'm wrong:
-4 and 5 is the heater (f) -> connect to PT ~6.3V tap
-1, 6 and 8 are not used (i.c.) -> don't connect (...)
-7 is the plate (a(node)) -> connect to through 470Ohm to B (320V)
-3 is the cathode (k, g3) -> connect through 220uF // 120Ohm to ground
-Now the one I really don't know: Do I connect 2 (g1) or 9 (g2) to the OT? What is the difference between these two grids and why are there 2 grids?

Number 3:
What kind of R's and C's does the amp have? I assume the R's are metal film, but can I use just about any type at these voltages? I know the ones in the power section should be high power (like 2-5W or so). Are the C's keramic? (except for the ones in the power section ofcourse).

[strangebru]

-Adding a bright switch as some people suggested, by switching the treble 'bleed' C between 100 and 470pF on the first gain pot. (Can anyone confirm if it is a little cleaner at high volumes with a higher C value?).


Welcome. I'm an EE also, and probably even more clueless on tubes. I have no plans to build my own, but it should be fun. After looking at Thomeeque's amp pictures, it was tempting though.

Anyway, at least I experimented with this bright cap. In the stock TT configuration, it cleans up the sound very nicely, but only when the gain is set below around 12 o'clock. As the gain is turned up past that it begins to grow more and more muddy. The real mud comes in as it transitions between 12 and 2 o'clock. Beyond 2, its like the normal muffled TT.

So to answer your question, with the volume on full and the gain at 12 o'clock, and using a humbucker, its pretty darn loud with respect to the amp's full power (which is all that one should compare it to). Also, it should be noted that at this gain, the amp has not yet gotten into its heavy distortion, it just begins to have some bite. With gain at 10, its very clean all around, but of course softer than at 12 o'clock. These levels are all a little less when using single coil.

Hope that helps.

[frank]

SOON TO-BE-IN-HOSPITAL NEWB ALERT:

Ok, so I tried to get an old Seymour Duncan EL84-powered amp back up and running... I did and it sucks. I'm gonna salvage what I can and use the shell and speaker for a TT. I've read a lot of you guy's posts and this seems like a fun and relatively simple project. ...but...

I'd like to try to use the power supply that I have, unless it's a bad idea, that is. So my question is: can the TT circuit tolerate the different voltages of my current PS: 340 at the CT instead of 325, 307 at the screens instead of 320?

I can already see some of you shaking your heads and going, "yeah, just make sure you've got your will in order..."

[Thomeeque]

Ok, so I tried to get an old Seymour Duncan EL84-powered amp back up and running...

This one (http://www.seymourduncan.com/images/support/amp_manuals/84_40.pdf), right? Lot of weird/unusual stuff in the circuit (especially in PSU and PA parts) - e.g. filaments feeding (two EL84 filaments in series), voltage doubler.. I'm bit sceptical that you could build reasonable TT out of this.. E.g. PT gives too low voltage for full 15W TT mode without doubler (and way too high with doubler).. I would advice you to try to sell it, if it works and buy original TT or proper parts for build.. If it's not the way, you could maybe start trying different preamp circuit preserving original PA part (maybe only preamp part sucks?)..

[frank]

Thomeeque, thank you very much for your reply.

Yes, that is the Duncan circuit I was talking about. I guess I'll just start from the ground up. I shouldn't be so lazy, I guess!

Thanks again. I'll do it right and we'll see how it sounds.

[John G]

Frank,
What HT voltage would be available if the PSU was configured as diode bridge connected..........Would the volts be enough ???

I wouln't right the amp of just yet, ( unless someone is going to pay a feww hundies for it ) if you can tame the high HT voltage you could do a dual switchable TT with 30W o/p, switch two 84s out = 15 W, and do a switcable single ended connection = 5Watts........could be interesting.
What speaker comes with the amp ?
Just thinking out loud.
John

[voxrules!]

"Inventing Terror
The Tiny Terror utilizes class A valve technology with a 100% analog signal path that eliminates any and all digital clipping output characteristics. Driven by a pair of EL84 power valves and a front end that utilizes a duct of 12AX7 preamp valves. Switchable from 7 to 15 watts of output, Orange designers have designed the gain structure of the Tiny Terror to work in a very unique way; utilizing a dual gang gain pot, one side turns up the first gain stage to the point of very heavy compression, while the other side changes the impedance of the second gain stage so that it to compresses to the same degree.

It utilizes a five section fully filmed interleaved output transformer that is very closely balanced to primary. The EL84 output tubes are cathode biased to around 90% in the 15w position, and 96% in the 7w position. In short, the Tiny Terror is designed to produce as much gain as a four stage gain pot, but the output tubes are driven evenly all the way through. The tone control is also designed in a unique way, where the tone circuit is not on the preamp side, but actually part of the phase inverter (power amp) so the gain structure of the amp is unaffected by the tone control. "

Sorry if I quote your quote :D

The old "class A blurb" again!!!

No couple of EL84 / 6BQ5 on earth ( don' t know about physics' laws in other parts of this universe, but that' s the way it is on this planet ) can produce 15-17 Watt of power if working in class "A" - PERIOD. I collect old datasheets, and have read a lot of them on the internet and the only way to get such output power from a couple of EL84 / 6BQ5 is a push-pull AB1 output stage - PERIOD - END

Even VOX claimed their AC30 to be working in class "A" and it has been proved that this too is a class "AB1" design with an output power of, guess what, 33 Watt ( 4 x EL84 ). An excellent article on this subject can be found on Randall Aiken' s website, and I encourage everyone to read it carefully.

I have recently expressed my opinion about "marketing" people, wouldn't things be better if they' d just say " buy this amp because it sounds good" instead of confusing customers with assertions which, in the better case are on the threshold of lying?

Class "AB1" amps do not necessarily sound any worse than real class "A" amps
( Marshall, Vox, Fender, Ampeg, Hiwatt, do they all ring a bell ? They' re all class AB1 designs! ). It' s all about taste and ear....but it can be said that virtually ALL the great ROCK/POP/FUSION/METAL...you name it - music of the last 50 years has been played through class AB1 amps, still there is someone that feels the need to add a "fake pedigree" to the stuff they' re selling - To me it' s simpler - you' re selling an amp which is a great sounding amp ? Simply say it' s a great sounding amp and explain the REAL reasons for it - In this case they COPIED the AC15' s to a good extent and added an extra gain section - as someone said - that' s no brain surgery - and AC15s/30s are cathode biased at the same static dissipation - about 15 W static ( please note EL84s are rated at 12 W max plate dissipation ) with a 50/100 Ohm resistor ( 4 or 2 output tubes ). Nothing new under the sun - PERIOD.

Regards

Bob

[iWishmaster]

This one (http://www.seymourduncan.com/images/support/amp_manuals/84_40.pdf), right? Lot of weird/unusual stuff in the circuit (especially in PSU and PA parts) - e.g. filaments feeding (two EL84 filaments in series), voltage doubler.. I'm bit sceptical that you could build reasonable TT out of this.. E.g. PT gives too low voltage for full 15W TT mode without doubler (and way too high with doubler).. I would advice you to try to sell it, if it works and buy original TT or proper parts for build.. If it's not the way, you could maybe start trying different preamp circuit preserving original PA part (maybe only preamp part sucks?)..

Based on what I've seen so far (and I nearly finished the construction of the amp, all but the EL84 section), the higher voltage on the plate shouldn't matter. It will change te sound and up the wattage a little, but I doubt this is for better or worse (the voltage will drop under heavy load anyway).

In my design, the CT voltage is around 350V, but the resistor at the cathode (bias) is 180 Ohm instead of 120 so the tubes run a little colder. The real reason for doing this is simple, I had some parts lying around I could salvage. This is the first time I'm building something with tubes in it, so I really hope it'll work out well. It should be finished tonight, so I'll let you know!

[Thomeeque]

Based on what I've seen so far (and I nearly finished the construction of the amp, all but the EL84 section), the higher voltage on the plate shouldn't matter. It will change te sound and up the wattage a little, but I doubt this is for better or worse (the voltage will drop under heavy load anyway)..

As I read the SD 84-40 schematics, there are two options when using original SD 84-40 power transformer: either use normal rectifier and get around 275 Volts or use doubler and get 550 Volts. I'd say non of these options is way to go when building TT clone..

But when thinking about this again, I can be wrong about those 275 Volts - when using two way (bridge) rectifier instead of doubler and with half power consumption maybe Frank could get to significantly higher voltage! Plus schematic does not say in what circumstances those voltages were measured. I still don't like filaments feeding concept very much (two EL84 filaments in series can lead to unbalanced filament voltages if these filaments electrically differ), but maybe it would not be as big trade-off as I have thought at first sight. Frank should do some measurements..

[iWishmaster]

As I read the SD 84-40 schematics, there are two options when using original SD 84-40 power transformer: either use normal rectifier and get around 275 Volts or use doubler and get 550 Volts. I'd say non of these options is way to go when building TT clone..

But when thinking about this again, I can be wrong about those 275 Volts - when using two way (bridge) rectifier instead of doubler and with half power consumption maybe Frank could get to significantly higher voltage! Plus schematic does not say in what circumstances those voltages were measured. I still don't like filaments feeding concept very much (two EL84 filaments in series can lead to unbalanced filament voltages if these filaments electrically differ), but maybe it would not be as big trade-off as I have thought at first sight. Frank should do some measurements..

I didn't look at the schematic before reading your post, you are right. Frank said however, the his CT and screen was only about 8% above the stock TT values. Where did you get this data Frank? By measurement or calculation?

[frank]

First I'd just like to say thank you to all who have responded. I am still pretty new here, and I already feel a lot of love. Thanks! There is a cool pioneering spirit here, and all in the name of good tone, so rock on!

The voltages I quoted before were from actual measurements, meaning I stuck the probes at all the points where the schematic showed voltages, and I was able to confirm that the voltages indicated on the schematic were (surprisingly) accurate. There was a variance of probably less than 5 volts at any given test point. The doubler, by the way, worked just like it should have.

The only problems I experienced, as I mentioned in another thread, was a wierd intermittent dropping of voltage once the amp heated up which I could only assume was a bad solder joint, since I could make it happen by lightly tapping on the HV parts with a drumstick.

I see what Thomeeque was saying about the SD circuit having a lot of strangeness. I don't know enough about this kind of stuff, but considering the original TT circuit has a CT voltage of 325V, I would think putting 550V there would slam something into a very "red" zone, or at least require me to do some maybe serious re-biasing. I think I may be playing with fire here. Unless you think it's a bad idea, I'm thinking of just tweaking the power supply to give the correct voltages, and I assume that would be almost the same thing as building a whole new PS.

Anyway, I'm glad you all care. As you can probably guess, I am just trying to save a dollar and some time by attempting to get electrons to flow without having to buy a bunch of new caps and resistors. But when all is said and done, I just want a good little amp to rock on, so I'll continue to listen intently to what you all say here, and probably end up doing the right thing in terms of keeping things to original spec.....

[frank]

Oh, I forgot to answer this post...
I don't know offhand what I'd get if I used a bridge rect. If I remember c