AC128 Ge transistors... is it possible?!?

[lazerphea]

Hi all!
Here's what happened to me while building a Ge Fuzz Face: I started breadbording it and made the mistake to use a negative ground schematic, so I was getting a crappy sound; I then corrected the mistake and the circuit sounded fine.
Perfboarded it, boxed it, sounded like crap again.
So I took out the board off the box, tested it because I was thinking I wired it wrong, but it sounded crappy anyway.
Then I assumed I made something wrong on the perfboard, maybe something I cannot understand because, to my eyes and to my DVM everythng was ok.
So I passed a week or so breadbording the circuit again and always got the same, terrible sound.
Depression and anger were getting stronger and stronger... how the heck could I make mistakes BREADBOARDING a simple circuit like that?? Maybe I'm eternally doomed to build just opamp buffers?
Maybe I'm going mad? Yes, it must be so, because sometimes, the circuit seems to sound ok, while some time after, the SAME circuit seems to sound wrong...
In the meantime I was reading, reading and reading again the great article "Technology of the Fuzz Face", by the almighty R.G., trying to understand what I was doing the wrong way: in the section about measuring the real gain of a Ge transistor, I read this:

if you're clever, you'll flip the switch and watch the voltage while you  put your finger on the transistor. Simple finger heat will make the gain rise rapidly.

Wow, these trannies are very sensitive! But... wait... let's do just the last try before trashing everything...
Breadboarded the circuit (so I touched the transistors), waited 10 minutes or so, tried it and hey! It sounds right! Lets try to put a finger over the first transistor: hey! It sounds crappy!
If you think I'm crazy, listen to it!
First part is played withouth have touched the first transistor, ending with a nice, long sustained Dmaj; between the first and the second part, I put my finger for about 5 seconds on the transistor, listen to the difference in the sound (it seems something's frying) and especially in the decay of the same Dmaj chord!

Now: is it normal or is it a rotten AC128? Maybe the first time I tried to breadboarding the circuit using a negative ground schematic I've ruined it?

[Renegadrian]

  really strage issue...

[darron]

have you tried replacing the bias with a trimmer maybe? sounds like its gating. not sure if it is because you damaged them/it. hmmm

[lazerphea]

Just a funny update: today was quite a hot day here in Italy, and I decided to play my Fuzz face, which sounded terribly: I then put it in the freezer, and after 10 minutes it sounded great! LOL!

[igerup]

Add a heatsink and small fan. Or even a peltier . Though the latter is probably a bit overkill for a fuzz pedal. 

[Scruffie]

Try adding a diode like this, might help http://fuzzcentral.ssguitar.com/3knob/3knobschematic.gif

Also... try switching Q1 & 2 around, or even putting a silicon transistor in Q1, might sort it.

[LucifersTrip]

First part is played withouth have touched the first transistor, ending with a nice, long sustained Dmaj; between the first and the second part, I put my finger for about 5 seconds on the transistor, listen to the difference in the sound (it seems something's frying) and especially in the decay of the same Dmaj chord!

I have to admit  I like the second frying, gated sound better. Would it be possible to visit a mortuary, hack off a finger and attach it to the
transistor permanently...

[Kinetic]

Would it be possible to visit a mortuary, hack off a finger and attach it to the
transistor permanently...

The finger would be cold 

[lazerphea]

LMAO!

[deadastronaut]

or carry a fridge around with ya ....

[Slade]

I have to admit  I like the second frying, gated sound better. Would it be possible to visit a mortuary, hack off a finger and attach it to the
transistor permanently...

^^^
I think Lucifer should be for the 666 competition.

[tubelectron]

Hi Lazerphea,

Darron is right :

have you tried replacing the bias with a trimmer maybe? sounds like its gating. not sure if it is because you damaged them/it. hmmm

This is probably a matter of bias. But you may have a very leaky AC128 transistor... Or have "leakened" it by your polarity mistake...

So check the Ice0 leak : you should not find more than 300µA to work properly with the original FF values. Check also the Hfe for Ib = 10µA, you should fine 80-120 to comply with the classic FF trend (thanks R.G. Keen's article as a reference).

Note : any transistor-meter function of any DMM is completely unable to measure a Ge transistor because of its Ice0 leak (which are negligible with Si transistors), so use the R.G. Keen's method for a good approximation of measurements on Ge transistors.

And yes, Ge transistor are very temperature sensitive - remember it when you will test it !

Air-conditioned Fuzz Face ? Why not... Unpractical device, IMHO...

A+!

[lazerphea]

Thanks for the advices!

[petemoore]

  Q2R bias trim with panel mount knob.
  Adjustment between 5k6 and 15k6 with 10k trimpot+5k6 stop resistor as Q2Cresistor.
  4k7 and 20k pot for wider range/misbiased tones/ semi-coarse fine tuning of bias.
  Figure out what is the temperature/bias range by trying different temperatures and bias resistances. I don't play well below 50 or 60 Deg. F., above 90 degrees the Distortion+ or Si FF get to play. Tonebender said: G kn neaphhkkezzzzzgh gk    ghh  gh    g   hhhh, once, then was removed from it's service position, one hot sunny day.

[LucifersTrip]

I have to admit  I like the second frying, gated sound better. Would it be possible to visit a mortuary, hack off a finger and attach it to the
transistor permanently...

^^^
I think Lucifer should be for the 666 competition.

Yes, you made me do it....and you knew I was never gonna use a normal enclosure...

[Brymus]

Try adding a diode like this, might help http://fuzzcentral.ssguitar.com/3knob/3knobschematic.gif

Also... try switching Q1 & 2 around, or even putting a silicon transistor in Q1, might sort it.

This works good in Rangemaster builds too.

[jasperoosthoek]

Hmm, it was a very hot summer for a week here. My room gets very warm as I have too much windows oriented to the west. Still that didn't keep me from wanting to nail that Woodstock/Red House tone!

My Ge Fuzz Face made from Small Bear transistors sounded just the same (lovely) as in the winter. Maybe tenperature variation varies for each unit :-D.