Anyone know what the "tiny terror" circuit is?

[Thomeeque]

Btw. YouTube - Tiny Terror Jule Mod

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]

TT

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]

"bright cap" replacement

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]

tubes on PRC TT

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 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]

Mercury Magnetics

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/page.../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]

TT Biasing

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/