There are too many variables, what B+ is on the EL34's is it close to or above +500VDC? What 6L6's do you plan to use, can they take the plate voltages? How hot are EL34 biased? Will the tubes red plate as soon as you put them in? Etc...
Like I shared, in THEORY many/most amps set up for EL34's will accept 6L6's, but not the other way around... again that is the THEORY, but you would need to look at the schematics to see what is going on and/or check the voltages/wiring on the amp itself... any good/decent tech can do this for you, but it requires paying them a fee for bench-time... which is prob on par with the cost of a set of 6L6's, so take your pick.
As Tom shared, if you want to play it safe then sub the EL34's for a 6CA7 or KT77, which is a safer bet.
Outside of that, you can take you amp into a decent tech and have him mod the amp to your liking. Personally, as I've stated before, better to sell off the amp and get something more akin to your tastes... getting a Marshall to sound like a Fender is a bit like putting a volvo engine into a volkwagen, the 2 don't really mix and won't be as efficient as putting the right engine into the appropriate car ?
Cheers
Matt
telefan100 wrote
Having said and listened to all of you - can I take a calculated risk and put the 6L6GCs in the Marshall just to hear what it sounds like?
Matt?
