Germanium transistors: I need some advice



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Germanium transistors: I need some advice

Postby agiant » Sun Jan 08, 2017 4:58 pm

I got some old Ge transistors and I want to start making my own pedals. I am a total noob.

I got these:

oc71:
leaks=77 Hfe=67.9
leaks=91 Hfe=32.5
leaks=141 Hfe=51.6
leaks=163 Hfe=49.5
leaks=209 Hfe=42.8
leaks=211 Hfe=62.7
leaks=212 Hfe=57.5
leaks=242 Hfe=76.4

oc72:
leaks=192 Hfe=39.4

ac128:
leaks=180 Hfe=75
leaks=183 Hfe=61.3
leaks=194 Hfe=60
leaks=137 Hfe=57.3
leaks=154 Hfe=55.6
leaks=129 Hfe=52
leaks=136 Hfe=50
leaks=130 Hfe=51.5
leaks=147 Hfe=48
leaks=140 Hfe=47
leaks=113 Hfe=37
leaks=130 Hfe=44
leaks=119 Hfe=44
leaks=134 Hfe=35
leaks=198 Hfe=33

I followed the Keen method to measure them (http://www.geofex.com/article_folders/f ... fftech.htm).

In some cases the gain is pretty low, right?

The question: what can I do with them? (especially with the low gain ones)

I'd like to start building some classics: a Rangemaster, a Tonebender MKII and a Fuzzrite.

Are they suitable for these pedals?

Thanks!
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Re: Germanium transistors: I need some advice

Postby Ben79 » Sun Jan 08, 2017 8:12 pm

Those are lowish gain for some of the transistors in those circuits but I think there is a way round by putting them in darlington pairs....this multiplies the gain so you'd end up with enormous gain but I think there might be a way round this with some resistors. Someone who knows what they're talking about will be able to shed some more light on this.
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Re: Germanium transistors: I need some advice

Postby cherler » Tue Jan 10, 2017 11:19 am

You can also use them as diodes for clipping if they're not usable for gain.
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Re: Germanium transistors: I need some advice

Postby crochambeau » Tue Jan 10, 2017 11:31 am

Cascade stages or plant your low gain Ge after a high gain stage of a different type (it's not like mixing matter and anti matter).

With single transistor circuits the value of the individual transistor are very important; as you add more transistors the individual defers to the group, sort of like people that way.
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Re: Germanium transistors: I need some advice

Postby culturejam » Wed Jan 11, 2017 1:26 am

Ben79 wrote:Those are lowish gain for some of the transistors in those circuits but I think there is a way round by putting them in darlington pairs....this multiplies the gain so you'd end up with enormous gain

You also end up with multiplied leakage and noise with darlington pairs. Just something to consider.
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Re: Germanium transistors: I need some advice

Postby eatyourguitar » Sun Jan 15, 2017 10:32 am

the darlingtons can have a low threshold for saturation and also a lot more non-linearity. I would expect a germanium darlington to act more like a comparator than an amplifier. if you like fuzz on your fuzz then darlington is fine. the numbers from the handheld tester are sometimes higher than the geofex method. you can use any method to test as long as you post what method you used. I think you can probably add 20HFE to some of those numbers and relate it to what you see on the forums. I think few people are using the correct geofex method now. most people use special transistor testers.
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Re: Germanium transistors: I need some advice

Postby agiant » Mon Jan 16, 2017 3:23 pm

thanks for the responses!

I followed the Keen method because I read that common multimeters (the ones with transistor tester) do not work well for germanium transistors ... I supposed that everyone were doing the same! It's pretty easy to do it well.
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Re: Germanium transistors: I need some advice

Postby eatyourguitar » Mon Jan 16, 2017 5:23 pm

the RG Keen method is a good standardized method but it is not the only one. therefor I would not say it is "better" exactly. but it is acceptable. the tolerances for the power supply, the resistors, the multimeter, the probes etc... is whatever people have on hand. the Geofex method does not have one specific tolerance unfortunately. a nice piece of equipment with known specs may provide a more accurate standardized test for transistors. how do people obtain regulated 9.0v supplies for the test?
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