thomaslattamiller

is it safe enough to change one of your valves in a marshall jcm2000 without having to re bias the whole thing? i changed the smaller ones but i blew out one of the larger ones

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DragonSarc

you can but you wont get the full worth of the valves - its better to rebias its easy check this vid - euro-q

stryker59

the smaller ones are the preamp tubes and you can change them without having to rebias......the big ones are the power tubes and you do need to rebias when changing them out..

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Adwex

It's not recommended, but it's possible. Just check the new tubes when you first power up to make sure the plates aren't glowing red like they're about to melt.

Also, if you can get tubes that draw the same current as your existing ones (they're "matched"), no need to re-bias. That's assuming of course that you know what the existing ones draw, which is not easy unless they came with that information when they were new. I bought tubes from Vacuum tubes @ thetubestore. New and NOS electron tubes for any amplifier. and they come with a number written on a label stuck to the tube that represents what current they drew when they were tested for matching purposes.

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