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Old 19th June 2017, 01:38 PM   #11
DIYBras is offline DIYBras  Brazil
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"New" amp with germanium transitors (AD161/162)

I liked the spirit of using an old amplifier. I made several amplifiers using old PCBs from commercial products.
Probably measurements for it differs from mine, due to silicon transistors usage.
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Old 19th June 2017, 01:48 PM   #12
DIYBras is offline DIYBras  Brazil
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Quote:
Originally Posted by Zero D View Post
I have a portable radio that uses GE transistors that belonged to my dad from the 1960's. I remember listening to it, & it still works & sounds nice as it did. Not HiFi, but a nice sound & has bass too None of that awful tinny sound many had !

All the best with your adventures
Thanks! (sorry about late response but now I have spare time)
Very cool to know!
This remember when I repaired a old germanium-based 60's radio with a cabinet sized like tube radios. Sounded very good with the first audio stage cap open. But that are the reason why owner asks me to repair: low audio gain. I replaced the capacitor and sound become less good, but surprising for a old radio with trafo coupled stages.
Famous people here in forum love old germanium radios (Telefunken Bazzajo in John Curl case).

One thing that germanium definitely have is a smoother crossover distortion due to "semi-remote" cut-off, helping in some cases. If I measure a silicon amp with class B bias, the harmonics will spray flat until the audio board response limit, but in case of this little amp, the harmonics have decay and stopped less than 50kHz, like in high bias/low bias graph.

I have other Ge amp but is a subject for another thread in future.
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Last edited by DIYBras; 19th June 2017 at 01:51 PM. Reason: Various bad spelling
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Old 19th June 2017, 02:36 PM   #13
Ketje is offline Ketje  Belgium
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Rather like this ?
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Old 19th June 2017, 05:27 PM   #14
DIYBras is offline DIYBras  Brazil
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This capacitor position seem to be strage at first glance, but it is a network "trick" (bootstrap) for making higher Z input. If you connect the capacitor like in your post, the input Z will be ~15k. In fact the stange connection is a positive feedback: in post #2, the open loop response has a huge peak at low frequencies, probably due a mismatch between capacitor values (is a side effect). In practice, my schema values makes a lot of motorboating, depending upon source Z input.

In fact, if low impedance is not a problem, I recommend to build one with your schematic modification. Will be far more stable.

Thanks for noticing this! So that I remembered this oscillation problem.
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Old 19th June 2017, 06:33 PM   #15
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Hi, I remember I built two amplifiers designed by Rockmandrake, you can search in the forum. I used them in my multi-amp with el. crossover experiments. High Zout was good for my woofer in open baffle ! ( I guess... )
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Old 19th June 2017, 08:30 PM   #16
Ketje is offline Ketje  Belgium
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Well leave the capacitor out all together.
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Old 20th June 2017, 03:06 PM   #17
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Originally Posted by DIYBras View Post
I have other Ge amp but is a subject for another thread in future.
I am interested :-) Generally wondering about Ge Transistors, I just purchased like 10 different types via ebay. Built my first amp from those and it sounds like it got a waterfall inside.
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