Low power Ge power amp

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I want to build a power amplifier using only germanium. It seems the key issue is thermal runaway.

I'm thinking something like this 2 watt (8ohm) design, except with possibly 2 or so transistors added for thermal stabilization. Using all 550mW (or whatever I can find pairs of) PNP and NPN trans. I also have a bunch of actual Ge power transistors in TO-3 packaging with gold plating meant for mabey 5 watts. I don't mind utilizing a +/- supply, 12VDC optimal.

The key to this unholy beast is drilling holes and mounting all of the transistors upside down inside a block of aluminum in fairly close proximity with a ton of thermal paste. (I believe)

Would something like this work? I know they did it somehow before silicon was invented. Academic and hobbyist fulfillment only, I know it's very inefficient.


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Early Ge transistors were mainly PNP so transformer-based class B was a common approach - if you can only source one polarity of transistor this is an approach (though you might have to make your own transformers :(.

Given the scarcity of Ge diodes for thermal compensation I'd suggest using a Vbe multiplier for bias voltage, more flexible than a diode stack. Note that the change in Vbe with temperature doesn't depend much on the type of semiconductor, its fundamental physics, so a 2 Ge output stage needs 2 Ge diodes for compensation or approx 2 x multiplied Ge Vbe.

The block of Al is a good idea, the thermal mass will help stabilize things, but I'm not sure how good early transistor packages are thermally.
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OH phoack yeah! Somebody finally doing something vintage. All power (well maybe low power) to ya! But I recommend sticking to a more "assymmetrical" design, meaning, one polarity on the output and use interstage transformer coupling. I can provide examples, but you can find them on the net, anyway. Finding matched Ge pairs will be difficult and expensive.


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> issue is thermal runaway.

The issue with Ge is *leakage*. Nailing all the parts together will not help. Si does not leak (enough to bother us) so Si-era tips do not apply.

Read-read-read!!!! Thousands of all-Ge power amps were made. Scour the hi-fi schematics boards. Also GE Transistor Manual. The magic is not lost, only forgotten.
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