I suspect this is due to the small thermal window of (then state of the art) germanium transistors which was still in widespread use. It wasnt until the mid 19

I suspect this is due to the small thermal window of (then state of the art) germanium transistors which was still in widespread use. It wasnt until the mid 1960s that the silicon transitor overtook germanium in terms of speed. And the USSR was many years behind the West, in terms of materials & design. Interesting related fact. The thermal operating range of germanium transistors was a concern even in the music world. The "Fuzz Face" pedal which helped give Jimi Hendrix his distinctive distorted guitar tone was built with two germanium transistors in a very simple circuit (< 5 components if I remember correctly). The distortion produced by this pedal was well known to change on stage, under hot lights or in cold basements, etc. To make matters worse, it was also sensitive to the supply voltage, so a fresh 9v acid battery would sound different than a dying battery. (ironically, the dying battery sounded better to most ears. The circuit only drew around 30 mV so a near-dead battery could still last a long time.) As a result, it was not unusual for working musicians to travel with several fuzzfaces and a pocket full of batteries, trying a few at soundcheck to see which sounded the best.