high screen voltage

[TarheelTechinTraining]

I'm looking for an EL34 that can handle at least 500v at the screen. New production would be best. Just can't afford NOS. Thanks in advance, Greg

[DRH1958]

I'm not sure if they really do handle this much voltage but the data sheet says so. Make sure you use proper screen grid resistors. Screen grid failure is the most common type for pentodes. Another option is to find a reputable seller on ebay and get good used vintage tubes. I've gotten several this way.
http://tubeaudio.com.au/content/tube_data/wc/EL34.pdf

[Enzo]

It isn't the voltage that kills this stuff, it is current. 500v on the screen is one thing, but you need to limit current, because those tiny screen grid wires can only get so hot before they melt. Those resistors mentioned by DRH are the way to do that.

If you ride down the road at 70 mph on a motorcycle and a mosquito hits your face, it is minor, but if a bird hits your face, then there is trouble. And a bowling ball will blow your fuse.

[TarheelTechinTraining]

Thanks Enzo. I needed a chuckle. My screen resistors are 220k. Should I lower them to 100k for more stability?

[Enzo]

220k screen resistors? You sure you are not looking at your grid resistors? I'd expect a screen resistor to be more like 1k, not 100k, unless someone has a better idea.

What schematic are you building from?

[TarheelTechinTraining]

My bad of course you are correct. 1k/5w on screen. I was looking at bias circuit.

[g1]

For a while, Marshall switched to 2K2 5W screen resistors. Not sure if it was for this reason, nor whether they still use them.