Mesa Boogie Mark IIB modification
- Thread starter legend58
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mayfly
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There was a thread awhile back about someone trying the same thing with a fender bassman. Give it a quick search and It'll come up.
A quick summary:
1 - EL34's use about double the heater current than 6L6s. If your power transformer is not up to it, you'll fry it.
2 - The bias will be at a completely different spot with EL34s. Boogies have fixed bias circuits, so that will have to be adjusted. I recommend that you replace the fixed bias circuit with a variable bias - ideally separately adjustable for each tube. Not major surgery, but will challenge you if you're not used to tube bias circuits.
3 - There are unused pins on the 6L6 that are typically used for handy spots to mount grid suppressor resistors and other components on the power tubes. These will have to be re-located. CB gave a good description of the work involved here on the other thread.
4 - EL34s have a different output impedance than 6L6 tubes. Ideally you'll want to change the O/P transformer to compensate.
5 - Finally, if this is your first time inside a tube amp, don't attempt this. You'll melt your finger tips off, burn your neighbor's house down and kill your girlfriends cat if you do. Don't say you were not warned.
A quick summary:
1 - EL34's use about double the heater current than 6L6s. If your power transformer is not up to it, you'll fry it.
2 - The bias will be at a completely different spot with EL34s. Boogies have fixed bias circuits, so that will have to be adjusted. I recommend that you replace the fixed bias circuit with a variable bias - ideally separately adjustable for each tube. Not major surgery, but will challenge you if you're not used to tube bias circuits.
3 - There are unused pins on the 6L6 that are typically used for handy spots to mount grid suppressor resistors and other components on the power tubes. These will have to be re-located. CB gave a good description of the work involved here on the other thread.
4 - EL34s have a different output impedance than 6L6 tubes. Ideally you'll want to change the O/P transformer to compensate.
5 - Finally, if this is your first time inside a tube amp, don't attempt this. You'll melt your finger tips off, burn your neighbor's house down and kill your girlfriends cat if you do. Don't say you were not warned.
