Post by Phil Allison
Most recent models from PV, Fender and VOX run their EL84s waaayyyy too hot and burn them out in short order.
keeps costs down, but requires frequent tube replacement. and so they
sell tubes. Sorta like the way HP sells printer ink.
A good power output tube should last for YEARS, without obvious signs of
the GE book tells me that EL84/6BQ5 has a plate dissipation of 12W. It's
a pretty fair bet that class AB operation would give you 12-15W RMS with
properly designed "everything". Squeezing more than that out of it is
going to kill the tubes in a short period of time.
the ref design in the GE book has 300V power supply and 8k p-p
transformer load (AB1) with a 130 ohm cathode bias resistor, for 17W
output [probably heavily distorted 17W]. I'm sure you could work out an
AB2 design with fixed bias to crank it up even higher, but that's not
necessarily good for the tubes...