JMG, I've worked on some high-class Russian made preamps and amplifiers in my day. You've got to love tube-type stuff (talking AF amps here) for supression of odd-order harmonics. Buttery smooth audio.
Also worked on my share of broadcast/amateur (ham) tube transmitters and transceivers too. Those were the days.
Now, all my ventures are solid-state. I had more "fun" working on tube stuff, though. Nothing like seeing old mercury-vapor rectifiers, or white-hot cathodes/filaments, and cherry red plates.
Kept warm in the winter time too! Now, 'dem were 'da days!
Charles