By normal volume the transistors don't need one.
The original article also states that to achieve nominal power, germanium transistors need a heatsink. When I turned volume up significantly, there was audible noise and distortion. The quality of this amplifier is just OK for simple home use with normal volume. These two require different transistors (that I don't have) and different values of resistors. There are also two other variants, one with lower power and one with higher power. Original article says that maximum power is 4 W. For the sake of completeness, I also display the schematics here. KiCad project is available for download below, on this page. This was without problems and played music on first try as well. I drew the schematics in KiCad and designed a PCB. The amplifier worked on a breadboard on first try. Besides these, also silicon transistors KC507 and KC508 are used and I had these as well. 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. When browsing through articles in magazine Amatérske rádio (05/1977, page 168), I stumbled upon an interesting schematic of audio amplifier with germanium transistors.
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