transformer check

[phillyhudson]

hi all - just need a safety check on transformers - I'm using the trannies from a peavey classic VT 50 [schematic included] and I've made a kind of JCM800 with EL34's instead of the 6L6's that the peavey trannies were designed for - it sounds great and I'm getting 476v @ 31.8mA on the plates and using the 8ohm output [there's only 4 or 8] into 16ohm 1x12 cab - anyone see any issues with this set-up ?

[martin manning]

Did you determine the primary impedance of the OT? If it's the typical 4k used for 6L6, it should be ok, but with the plate voltage being that high beware of red-plating if it's played at high volume for an extended time. If there is some significant sag in B+ at high power it should be fine.

[phillyhudson]

yes I've not checked the primary impedance , should I maybe try a high wattage sag resistor before the choke ? - every time I've tried those things in the past it reduces the voltage significantly but causes a worrying amount of heat - is there any other way of reducing the potential for red-plating ?
I know I'd be better off just buying whatever works for that circuit but I already had these trannys lying around and wanted to save some money

[Helmholtz]

Don't forget that EL34s definitely need (individual) screen resistors of at least 1k.

[phillyhudson]

thanks helmholtz - got 1.5k on there