Originally Posted by rds
Thanks to everyone who made time to solve this hum problem.
My search at Digikey shows that a 50V 330uF Nichicon PW
Good except that is not a low impedance cap.... I'd like to see some sort of low impedance cap
there, but it's not as critical that it is low impedance cap as all the others in the heater circuit.Add me to the hum-less
Only low impedance 35v+ caps I could fit under my PCB were two 100uf - 63 volters. So total 247uf for C3H & no hum whatsoever with tubes that had no hum w/battery heater supply (6922 & 6DJ8 that did have some hum w/stock 47uf C3H).
IOW I find CTH using onboard switcher with 247uF of C3H capacitance indistinguishable from disabled switcher/battery powered heater. It's an even more wonderful amp than it was before
We are done with this issue I think. So just consider pulling stock 47uf C3H & replacing w/10mm dia - 20mm height (max size) 330uf 50V low imped cap.