Convert from 6L6 to EL34s?

[SlyStrat]

Can any tube amp be converted from 6L6 to EL34s? If so, whats involved?

[hasserl]

The pin out is the same with the exception of pin 1, which is tied to pin 8 internally on a 6L6GC, but not on a EL34 (not on metal tube 6L6 either). So to use El34's you have to makes sure Pin 1 in connected to ground.

Also, EL34's tend to use larger screen grid resistors than 6L6's, so it's not a bad idea to increase the value of the screen grid resistors to say 1k (5w).

Another thing is El34's draw more current for the filaments than do 6L6's, which might tax the power transformer if it is not sized large enough to handle the extra load.

And finally, EL34's have slightly different impedance needs than 6L6's, i.e. a common 50 watt Marshall EL34 amp would have a 3k4 load on the tubes where a typical 40 - 50 watt Fender 6L6 amp would have a 4k load on the tubes. Which personally I wouldn't worry about, though you could try different impedance settings if your amp has an impedance select switch, to see if you get better response with one over another.

[SlyStrat]

Thanks.
How would I know if my transformer can handle the EL34s.

[hasserl]

One way is to measure the filament voltage of the amp with 6L6's in place, then measure it again once you have EL34's in place. If there is a sizeable drop in voltage that would indicate the supply from the transformer is on the low side. Also feel the transformer for heat buildup. The danger to the tranny is failure of the filament coil in the transformer due to heat buildup. Trannies can get hot to the touch anyway, so that is not the ultimate test, unless you've got a temp gun and can record actual temperatures. It's hard to feel slight differences in temp by hand. But if it runs nice and cool with 6L6's and get's real hot with EL34's that indicates a problem.