"Stev eH"
StevehkhhSDJvhvbjjxbvvbhnvbhzjdnxzvzhzdshbvnjzvnb vnvjbvbcjbvvvvnmxvzjhjzsdgfgsfghgjsghgsljhglhdjfgh fufgfhzysgfhczgugfvzlvufzvllgfzlyfyvlgbylvdfghvbly
wrote in message ...
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. I'll bet you wondered why the filaments were so bright.

To properly measure this voltage, you need a true RMS voltmeter. Most
inepensive AC voltmeters actually measure the peak voltage and display the
result on a scale calibrated for a sine wave input. RMS (root mean square)
is the equivalent DC voltage that would produce the same HEATING in a
resistance as the applied waveform.

Most hams are quite confused by this. Looking over some websites
explaining this, one of the better ones is a Google Book Search of
"Electric Machinery Fundamentals" by Stephen J. Chapman who presents the
mathematics in detail starting on page 163:
http://books.google.com/books?id=ltg...m=10&ct=result

As an interesting side note, the Philips datasheet on the PL519 is the
first I have seen that explicitly discusses Barkhausen interference and how
to suppress it.

73, Dr. Barry L. Ornitz WA4VZQ