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4W amplifier with germanium transistors

.When browsing through articles in magazine Amatérske rádio (05/1977, page 168), I stumbled upon an interesting schematic of audio amplifier with germanium transistors. I had these in my spare parts box, from dismantled electronics, so why not give them a new purpose? Namely, the transisors are GC510 and GC520. Besides these, also silicon transistors KC507 and KC508 are used and I had these as well.

The amplifier worked on a breadboard on first try. I drew the schematics in KiCad and designed a PCB. This was without problems and played music on first try as well. KiCad project is available for download below, on this page. For the sake of completeness, I also display the schematics here.

Original article says that maximum power is 4 W. There are also two other variants, one with lower power and one with higher power. These two require different transistors (that I don't have) and different values of resistors.

The quality of this amplifier is just OK for simple home use with normal volume. When I turned volume up significantly, there was audible noise and distortion. The original article also states that to achieve nominal power, germanium transistors need a heatsink. By normal volume the transistors don't need one.

Some people say that germanium transistors have a different, "softer" sound, close to vacuum tubes, so I was curious about the difference. It indeed sounded a little different, or was I just telling that to myself?

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