What About Darlington Germanium Transistors?

Chuck D. Bones

Circuit Wizard
Is there a way to make use of low-gain Germanium transistors? Can we build a Darlington pair from Ge transistors? These are good questions and pedal designers have been dealing with the problem of low HFE transistors from almost day one. If you want to see an example, you need look no farther than the Tone Bender Mk III and Burns Buzzaround. Refer to the PedalPCB Gnat schematic. Q1 & Q2 form a Darlington pair. Leakage multiplies the same way that HFE does in a Darlington pair, which is why the designers put R4 there.

So there's the answer. But as they say on TV: "Wait, there's more!"

Q2 does most of the heavy lifting re: distortion, so we could make Q1 silicon and get pretty much the same tone. Now leakage is less of a problem and we can get rid of R4.

Another alternative is to build a Sziklai pair and make both trannies Ge or construct a hybrid circuit where one of the transistors is silicon or a JFET. The only hard part, and it really isn't that hard, is sizing the resistors.
 
Maybe an obvious question: I suppose it’s not possible to come up with a configuration that’s a drop in replacement for a high gain Ge transistor? I’m thinking about all the existing circuit that use them and how rare high gain ones have become…
 
Guitar PCB has some on sale.
What circuits require high-gain Ge trannies? I can't think of any off the top of my head. 90% of the MP38As and P28s I have are in the 50 - 100 HFE range and work very well in the circuits I build.

The Sziklai pair is the closest you'll find to a drop-in replacement. Darlington is a close second.
 
Guitar PCB has some on sale.
What circuits require high-gain Ge trannies? I can't think of any off the top of my head. 90% of the MP38As and P28s I have are in the 50 - 100 HFE range and work very well in the circuits I build.

The Sziklai pair is the closest you'll find to a drop-in replacement. Darlington is a close second.
I stand corrected! For some reason I thought there existed Ge transistors with hfe of 200 but it sounds like even 100 is high. TIL.
 
Clipping diodes.

I have quite a few 2N1308 & 2N1309 with HFE over 200. They don't sound particularly good in Fuzz Faces.

Here's test data for my hottest Ge tranny, a 2N1309. The curve tracer corroborates the CCTT result. With high HFE comes high Iceo and strong temperature sensitivity.

high-gain 2N1309 - 02.jpg

2N1309 HFE = 473 curve trace.png
 
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