I have Motorola data books from 1970, and the Germanium transistors were truly poor compared to the modern ones, most would struggle to get to 30V with leakage under 1mA, and the power devices were even worse, some proclaimed low leakage of 10mA. 400V was a dream, and only available in some then ultra expensive and exotic silicon devices, with horrid spread. Highest power device was a PNP 30v darlington transistor array, capable of handling 60A, with an impressive size, and even more impressive price. IIRC leakage at 30V was quoted as "Under 100mA". So, yes, to get good results and 400v you needed hot cathodes, and good design to make it stable.