Can I put 2 EL34's in my Mark III if it's a non-simulclass?

[xT00BZRG00Dx]

It's a 100 watt head with a half-power switch. Can I put in EL34's?

 

[stephen sawall]

Putting a adjustable bias on the Mark amps is pretty easy. With that you could put a number of tubes in there. The bias range of EL34 and 6L6 are not that far apart. The power tube sockets may need to be rewired also. This is not a big mod to do.