Fuzz Face clone - Ac128 hfe

[davidhaus]

Hello Guys,

I wanna build a Fuzz Face clone using two AC128s i got on ebay.
Unfortunately they are both in the same hfe range of about 70-80.
The second Transistor should have hfe of 110-130 approx. according to this site:
https://www.electrosmash.com/fuzz-face

Can i still use them, or will it sound shit?
 

[idy]

Socket them, try them.

There's plenty to read about this, it's been hashed over many a time.
Did you test for leakage? Real gain may be even lower.

The quoted figures are from testing "known good" examples. But some folks like different...

[Electric Warrior]

The quoted figures are from testing "known good" examples. But some folks like different...

It's what some builders like, but not necessarily how Fuzz Facs were made back in the 1960s.. The transistors used were often closely matched. Hfe spec for the NKT275s Arbiter used was 30...90. I haven't seen too many hfe readings, but they're often in the low 50's and 60's with a fair amount of leakage (which is necessary as low gain transistors with too little leakage don't bias right).

The bias voltages Electro Smash quotes are BS. They look as if someone fed hfes for low gain silicons into a Fuzz Face voltage calculator. With germaniums in the right ballpark, Q1C should be measuring between -0.3 and -0.65 V. If it doesn't, tweaking Q1's collector resistor will help. It sets the voltages for both transistors as Q2's collector voltage mostly depends on how Q1 is set up.

[rankot]

I was measuring my AC1xx transistors and found one with hfe value of 5 and another with 8. Is there anything I can do with them besides using them as clipping diodes? Is it possible to make a Darlingtone pair?

[tonyharker]

How did you measure them?  Sometimes the "intelligent" testers do not recognise germanium transistors with higher gains and swap collector and emitter to get the reading.

[antonis]

Is it possible to make a Darlingtone pair?

Only if a total gain of 40 makes you more proud..

As tony said, you probably measured individual gains the "wrong" way..

[rankot]

How did you measure them?  Sometimes the "intelligent" testers do not recognise germanium transistors with higher gains and swap collector and emitter to get the reading.

Yes, maybe that is the case. I have measured with GM328A transistor tester. Will try those two weakies another way

[j_flanders]

The bias voltages Electro Smash quotes are BS.

Q1C should be measuring between -0.3 and -0.65 V.  If it doesn't, tweaking Q1's collector resistor will help.

have Q1VC=-0.5 to -0.7 and Q2VC=-4.5V. substitute R1 and R3 so the VC of the transistors can be easily adjusted.

If you click the image/schematic with the wrong bias voltages it opens a new one but with correct bias voltages:
https://www.electrosmash.com/images/tech/fuzz-face/fuzz-face-bias.jpg