[Boater Sam]

Took all the valves out of a radio chassis to turn it and replace a few caps. It was working OK.
Replaced the 5 valves, the EZ80 had been replaced with an EZ81 and the output was a used Russian EL84 equivalent. Assumed (ha!) that the tall valve was the output valve, nearest the output transformer wiring.
Strange, its not working now. Oh, the rectifier is glowing bright, oh, now its sparking over inside. Duff rectifier.
Fast off, pull it out, oh heck its a pentode, the output valve !!!
Yes, I'd put them in the wrong sockets.
Even stranger, with the same valves in the right holes, it works just as well if not better than before!
Tuff beggars these Russian valves.