3AX31C Germanium gain

M

makisushi

Member
I ordered some germanium transistor from AliExpress before I knew eBay was a better source. The gain is all over the place with theses AX31C. I'm currently working on a tone bender and fuzz face pnp. Where should I start in term of gain ? I'm also waiting for more germanium from eBay
 

Attachments

  • IMG_20250529_103145141_HDR~2.jpg
    IMG_20250529_103145141_HDR~2.jpg
    307.9 KB · Views: 17
I also bought a batch of these and had to trash most of them.

Which Tone Bender? There are at least 4 different circuits.
 
makisushi said:
The tayda one. Waiting for the pump charge inverter.
Click to expand...
Is the Tayda PCB a Tone Bender Mk. I? Mk. 1.5? Mk. II? Mk. III? Each one is a very different circuit. With that said, leakage will matter more than hFE. I’d recommend breadboarding the circuit before building it, especially if it’s not a Tone Bender Mk. III.
 
I don't know which version it is. They are using 3x 2N3904 for the NPN version, so 100 hfe +? . I use socket for the transistors so I can swap them... Does leakage needs to be high or low? do they all need to be around the same values or one pair and one other?

Tone Bender

This is the Tonebender, one of the most iconic fuzz effects from the 60s.
www.taydakits.com
 
here's the recommend value from Tayda but can I really use 3 differents gain with 2 bias?


Q1: β = 70-90
Q2: β = 50-70
Q3: β = 110-130
 
It's the MK2 then. A Fuzz Face with a transistor stage in front.
Those are the gain ranges. You want leakage in Q2 and Q3 above 100uA.
Q3 should be around -8V
 
Might as well share my experience here. I've never built anything Germanium, and I'm not sure I fully trust the DSO-TC4, but I ordered 10 each of 3AX31C and 3BX31C, just to see what sort of parameter spread you might get. Not sure if any of them will be useful for a circuit?

3ax31c.jpg
3ax31c-tester.jpg
3bx31c.jpg
3bx31c-tester.jpg
 
rossbalch said:
Might as well share my experience here. I've never built anything Germanium, and I'm not sure I fully trust the DSO-TC4, but I ordered 10 each of 3AX31C and 3BX31C, just to see what sort of parameter spread you might get. Not sure if any of them will be useful for a circuit?

View attachment 98004
View attachment 98005
View attachment 98006
View attachment 98007
Click to expand...
The leakage is off the chart for all of them. In line with my experience when I bought a batch of these transistors. Unusable, I would say.

I consider low leakage any value below 100uA. For circuits that require leakage, I would go 100-300uA. Above that usually sounds noisy and overall bad.

Low gain to me is 50-80 hFE. Useful if you have hot pickups, otherwise weak.

If you have a breadboard going there's no harm popping these in to see what happens. Try a Germanium Fuzzrite. It will be gated with that leakage, which is great with single coils.
 
andare said:
The leakage is off the chart for all of them. In line with my experience when I bought a batch of these transistors. Unusable, I would say.

I consider low leakage any value below 100uA. For circuits that require leakage, I would go 100-300uA. Above that usually sounds noisy and overall bad.

Low gain to me is 50-80 hFE. Useful if you have hot pickups, otherwise weak.

If you have a breadboard going there's no harm popping these in to see what happens. Try a Germanium Fuzzrite. It will be gated with that leakage, which is great with single coils.
Click to expand...
I wonder if the Chinese germanium bubble has already burst? Seems no one recently has tested any of worth. I might try them as diodes.

I'm not really a big fuzz guy. More preamp type circuits. Maybe some Darlington pairs could work? But even then I think the leakage is too high?

I bought a box of P416B from our trusty neighbourhood Ukrainian ebay seller. Hopefully there's some useful ones in there.
 
I do need to try the RG keen method too. I don't know how much I trust the TC4. Really useful as a sig gen / oscope but probably not as reliable for transistors.
 
rossbalch said:
I do need to try the RG keen method too. I don't know how much I trust the TC4. Really useful as a sig gen / oscope but probably not as reliable for transistors.
Click to expand...
I use a TC1 tester and it has served me well. The RG Keen method works better if you rig it up but I decided it wasn't worth it for all the junk parts I buy :)
 
You must log in or register to reply here.
Back
Top