Weird though transformer is 330-0-330v and I'm using a 5Y3. For some reason I thought the Voltage was lower last time I worked on it. ... I was very supprised when I measured 380V because I didn't remember that. Shouldn't 5Y3 voltage be about 1.1 X A.C. or is 40mA not enough to sag it that low?
For
all rectifiers, start with VAC * 1.414 to find peak voltage. 330vac * 1.414 = ~467v peak
Voltage drop from peak depends on
at least rectifier internal impedance, current drawn and filter capacitance. If rectifier impedance drops, current draw drops or filter capacitance increases, the resulting d.c. volts go up. Then there's the issue of supply impedance contributed by the power transformer windings; this can vary by manufacturer and model-to-model. And any resistance you add along the way.
So you landed at about 100v below the peak output voltage of the rectifier (maybe about as much as you'll drop due to that). BTW, if you used a 20uF filter cap as shown in the
G.E. 5Y3 data sheet you would land above 400vdc at the filter cap (if you had ~50Ω supply impedance due to the transformer), while using 10uF like the
RCA 5Y3 data sheet drops the voltage closer to what you have.
... Shouldn't 5Y3 voltage be about 1.1 X A.C. or is 40mA not enough to sag it that low?
Remember this was just an observation some builders made, but is not a "rule" that always applies. It implies if your PT was 200-0-200v you'd get 220vdc output (~63v dropped from peak voltage), while a 500-0-500v PT would give you 550vdc (157v dropped from peak). That scenario is actually incorrect; the "times 1.1 observation" actually only holds true over a narrow range of operating circumstances where the observation was made and ignores the multiple competing factors that are at play.
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