Thanks to all who replied to my request for help with filament transformers
for my 4CX1500A.
Now I have another question about something that never occurred to me
before. For a zener regulated screen supply, what value of screen current
do you use to calculate the proper value of the series dropping resistor?
There is the average screen current under load that the screen current meter
reads, and than there is the instantaneous value of screen current that
occurs at the minimum of the plate voltage swing which is much higher.
According to my calculations from the constant current curves for a
4CX1500A, the average screen current will be about 20 mA while the peak
screen current will be about 100 mA. I guess I really need to use the 100
mA figure for the load on the value of screen current as well as consider
how much the transformer output voltage will sag when it is under the full
load of tube screen current and the screen bleeder resistor load.
David C. Hallam
KC2JD
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