I have an old Peavey Bravo - 2xEL84 1x12 combo. I have made a few minor mods to it and changed the speaker - it is a killer little amp now. Anyway, I just put some new sovtek El 84's in, and 1 crapped out after a couple hours, which prompted me to look into it a little. I measure 385 volts at the plate, and from everything I read, this is higher than the norm. I am going to install a standby switch this weekend. A few questions, thanks in advance for any help.
1) should I decrease the B+ with a couple or 3 zener diodes in series with the bridge rectifier to bring it into the 350 volt range?
2) will letting the tubes warm up for a minute before flipping the standby on really help prevent tube failure and extend their life?.
3) I didn't measure the B++ or other B+ "derivative" voltages for the preamp tubes, but will lowering the supply voltage by 35 volts have an ill effect of them? - what is the accepted voltage range for them?
4) I haven't checked the bias on this amp (no adjustment pot) - Peavey shows -18v on the schematic - does that sound right? I have seen -12v listed for EL84's elsewhere...
5) will lowering the B+ by 35 volts necessitate a re-bias, or cause the tubes to draw excessive current?