EL34/6CA7 from eastern countries are the same as their rectifiers. In Australia we made quite a few amps using EL34/6CA7, and even the origional Mullards fried when used at "maximum" ratings. Thats 775 volts on the anodes, and 400 volts on screens, 11,000 ohms plate to plate load. 100 watts was the supposed output from a single pair. The amps like this fried regularly, usually taking out the output transformer with it.
As far as using silicon rectifiers, the latest Fender AND Marshall amps I have worked on, have valve rectifiers with silicon diodes strapped across them as well. WHY
I dont know. They do appear to be a bit more reliable though. Sovtek and Svetlana I put into the same bag as my first post. Golden DRagon are Chinese and I havent used any. Groove Tubes are also in the same boat, i.e. Chinese and have a name for being very noisy. Their rectifiers in particular giving the amp various popping and clicking noises which can be very annoying in the studio.
Joe