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.
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.
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.
> 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.
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.
I Built one in 1967 ( with preamp, phono input, bass treble control).
2x 10 W rms.
Class A.
Single voltage 32V stabilized.
Big cap to 8 Ohm speaker.
Quasy output stage.
Output transistor PNP TO3.
Drivers PNP and NPN TO5.
2x 10 W rms.
Class A.
Single voltage 32V stabilized.
Big cap to 8 Ohm speaker.
Quasy output stage.
Output transistor PNP TO3.
Drivers PNP and NPN TO5.