Power Tube change questions

[MickeyB]

Built this Ampeg SB-12 clone with 6L6's and thinking of trying EL34's in it. I know about adding in pin 1 but have a few other questions. Plate voltage is 380v, different rectifier?, increase 1k resistors? other tweaks?
Thanks,
Mick

[kleuck]

380 volt should be right, 1K screen resistors (3 watts mini) would be a good idea, even with 6L6 ; bust the best mod would be to turn the fixed bias into an adjustable one.

[stokes]

Cant see the schem you linked clear enough,but looking at another schem I have for the B-12 it shows a 39k resistor on the outboard side of the bias diode,connected to ground.I would change that resistor with a pot of about 2x's the value,in this case 80k,not a common value so I would use a 100k cermet pot.You will then have an adjustable bias.You will have to adjust the bias for the EL34's.Just connect pin 1 and 8 at the socket,make sure there is nothing connected to pin 1.Sometimes these unused pins are used as a connection point for something else.