I just got a JCM800 4212 that came w/6550 power tubes. I was wondering if I can swap those for KT88's or EL34's without modification. At the very least what would be a good direct replacement power tube? Thanks in advance.
Originally Posted by iceman79I just got a JCM800 4212 that came w/6550 power tubes. I was wondering if I can swap those for KT88's or EL34's without modification. At the very least what would be a good direct replacement power tube? Thanks in advance.
If you switch to EL34s you will have to have the bias resistor(s) changed so you can bias the different tubes....Not sure about the KT88s cause I've never used them?
KT88 's are a heavy duty European 6550. It's much like the EL34 and the KT77, or the EL34 and 6CA7. The original Gold lion KT88 exceeded the performance of the American 6550 by a lot, but current production chinese/eastern europe KT88's are probably close to old stock 6550's. KT88's should go right in and bias up fine. Old 6550's were so tough that they may still be good too. Some JCM800 era Marshalls with 6550's can be improved with a simple rebias adjustment too. An alternative may be the 6CA7 reissues. It treads the middle ground in between a european EL34 and a 6550. The 6CA7 was what EVH used, but NOS examples are long gone or super expensive now. What ever you go with, a bias adjustment will need to be made and possible minor modifications to the bias circut. Some Marshalls can go from 6550's to EL34's without modification and some can't.
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