On Dec 4, 9:26*pm, "NoSPAM" wrote:
"Stev eH"
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wrote in ...

My first amp had 3 PL519s with a lethal power supply using a voltage
tripp{l}er direct off the 240V mains, heaters were direct off mains via a
1n5406 diode. It's still up in the parents loft somewhere, must dig it
out over the holidays and give it a try....

Steve H

Do you realize that the RMS value of half-wave rectified AC is not one half
of the applied RMS voltage but rather 0.707 of the applied RMS voltage. *So
your three 40 volt filament PL519s actually saw about 56 volts RMS across
each filament.

Hey OM
I beg to differ. As any casual observer can see that peek is 330V and
the average would be 0.363 of the peak so that's 40 volts in my
calculator all day long, for a 3 tube string.

Lets take a square wave, the average would be 0.5 of peek, far lower
than 0.707 you are used to using. Even if it was full wave 120 cycle
dc, the average would only be 0.636 still lower than 0.707.

I tell you what. Take a diode and rectify the mains with it and
measure the DC voltage with a DVM, VTVM or a VOM and 0.363 of peak is
what you will get for a DC voltage on that meter. Or do the real
integral of the dv/dt and see for yourself.

The TV repair business I was in manufacturers put 50volt peak on a CRT
6.3volt filament, the average voltage was 6.3 volts. Lets see you RMS
that one.

73 OM

n8zu