I think I might still have a few germanium transistors up in my loft - along with a load of junk collected over the years. I am surprised at how many transistors they use in parallel - although that is the only way to get the power. I find myself wondering how they ensure that they share load evenly. Early in my career I was involved in production tests on railway rectifier equipments and as the largest silicon diodes were 100A, we used a lot in parallel per phase on long heat sinks. We had to check the voltage drop of each diode on each heat sink to ensure that they shared current well. If there were any highs or lows, we had to replace the particular diodes or swap them around. As you might imagine, this was an extremely tedious job. These units were also air cooled, with large and noisy blowers.