I have an amplifier with a pair of 3-500Z's in it. I have very high local
feeders, 248VAC, which gives me excessive filament voltage on the pair of
3-500Z's. I did put a pair of jacks on the back of the amp, which is part
of the pressurized compartment for cooling, and set the voltage with a
series of 20 watt resistors in the filament primary to get the voltage down
to 5.01Volts AC, Measured with a Simpson True RMS meter, Amp NOT keyed, ZERO
plate current. I played around with various resistors in series with the
jacks to get rid of the RF when the amp is keyed, about 300 ma of plate
current into a dummy load, properly tuned and loaded. I cannot get
consistent voltage readings at all. I have no Idea what the voltage is
under load! I did try to look up a schematic for a Collins 30S1 on the
http://bama.sbc.edu/images/col-ltr.jpg web page, (had a letter from Collins
saying schematics cannot be posted anymore) as I knew that amp had a
rheostat to adjust the filament voltage. Can anyone tell me what values,
components and tips I should use to obtain a more accurate and stable
voltage reading?
Regards
Monty/WB5GLB
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