Anyone know what the "tiny terror" circuit is?

[strangebru]

That was it !

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!

[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, 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

[Robert M. Martinelli]

"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

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