'Modern' germanium transistors

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'Modern' germanium transistors

Postby Gary_W » 21 Feb 2013, 16:15

Hello all,

Whilst I've built plenty of stompboxes in my time, my dabblings with germanium have been few and far between. I've built a fuzz factory and it's good BUT I'm now wanting to do a 'traditional', properly biased germanium fuzz face and also to play with low-gain transistors / a few different values to do a Sun Face clone (my understanding is that low gain transistors are used there? Can anyone confirm please?).

I keep seeing general comments that 'modern' germanium transistors just do not cut it.

If this is true, we are all at the mercy of the snake-oil salesmen...... Many of the remaining oldies are going to already have been deemed too leaky to be of use in a fuzz but are still happily being sold on due to us all being made paranoid that modern ones aren't good enough. As every dirt box / fuzz on my board is home-made, I'm struggling with the idea of paying a pro £300 uk for a pair of trannies that are properly biased just because they are old ones and therefore 'better'.

So what is it that made the old ones special? My thinking on a germanium transistor is that you can measure it for leakage and gain and then, depending on type, it will have a certain amount of capacitance going on.

I'm clearly missing something - can anyone tell me what other things are important? Why is a modern germanium with low leakage and suitable hfe any worse than a 1960's NKT275 with the same measurable ratings that is going for crazy money and, of course, may not be genuine anyway? I've seen articles here whereby a silicone fuzz can be taken in a germanium direction by adding a bit of extra capacitance across the transistor.....

Please be aware that I am not claiming there is no difference - I have very little experience at this. I'm just trying to understand what the difference actually is and how obvious / subtle. Is it the case that, if you bias it right, you'll get 98% there with any germanium that fits the leakage and gain requirements or is it that even then it'll still stink compared to a NOS?

I have some NOS AC128's on the way, all tested for low leakage and all sorted into gain ranges - they were only about £2.50 each. As I recently saw a supposed pair of NKT's on eBay for £85 I'm obviously keen to understand the difference..... I'll attempt to make a Sunface and, if that goes well, will do a Beano boost to go with and therefore create a homebrew Sunlion. I note with interest on the Analogman site that he says that the AC128's 'don't sound good'. He's clearly a superb builder and, if I don't get sounds I like, I may bite the bullet and buy the originals........ but the cynical side of me points out that it makes sense to talk up the rare thing you have that is unavailable to most DIY folks and to talk down the dirt cheap NOS things that are readily available to all..... I'm not trying to be insulting or confrontational there - it's entirely possible that the NKT's are a league above anything else. But I just don't know and have no simple way of a/bing.

Many thanks

Gary
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Re: 'Modern' germanium transistors

Postby beedotman » 21 Feb 2013, 16:58

Gary_W wrote: (my understanding is that low gain transistors are used there? Can anyone confirm please?).


In 'normal' AM Sun Face version gains are in 50-60hfe buckets, so rather low...
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Re: 'Modern' germanium transistors

Postby Gary_W » 21 Feb 2013, 17:03

beedotman wrote:
Gary_W wrote: (my understanding is that low gain transistors are used there? Can anyone confirm please?).


In 'normal' AM Sun Face version gains are in 50-60hfe buckets, so rather low...


Thanks for this - is this for both transistors or is there still a stagger of a lower gain feeding a higher?

I have gain ranges coming from 40 up to 80 and I've got some 120's laying around so should have the bases covered (pun fully intended :wink: )
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Re: 'Modern' germanium transistors

Postby beedotman » 21 Feb 2013, 18:59

If I remember correctly - first one was with 55hfe second one with 60hfe or something like that.
But there's no magic numbers really. Just swap transistors till You find best sounding pair for Your ears.
I like something in 65-90hfe bucket.
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Re: 'Modern' germanium transistors

Postby Gary_W » 22 Feb 2013, 00:28

Many thanks - I really appreciate the reply :)

Can't wait to get cracking with the build. If only the postman loved me it'd be halfway built already....
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