12 watts rated output from a pair of 300Bs in parallel seems low, so maybe the plate voltages are that low...? Seems like a very unusual approach, but there are a lot of unusual things about this amp.
We don't know the resistance of the secondary windings on the power transformer, so that's an estimate in the PSUD model.
David McGown wrote:
Dave, Grover,
I modeled up the power supply in Power Supply Designer (PSUD2) just for kicks. It is a full wave rectifier (not bridge) with doubled up plates on the 5U4, and from what I can tell the power transformer taps are 250V-120V-0-120V-250V (note the schematic lists voltage between taps, not the voltage at each tap), Assuming the plate current on each 300Bs of around 85 mA each, plus 15mA for the driver section, I get only around 225V B+ on the plates.
That seems to be a really low operating point, so maybe I am misreading the taps on the transformer. Any case, the current through the 5U4s stays well below limits at the initial charging of filter caps. Now if the voltage is actually higher, (say if the voltage between the first tap and second is 230V, therefore a 350-120-0-120-350 or 700VCT transformer), which is more like I would expect for a 300B amp, the dual rectifier is at the current limit at turn-on for a single cycle. That is probably fine, since the datasheet max transient current is actually much higher than the value used in PSUD (4.6A per plate vs 1.6A in PSUD). So I think the Manley rectifier setup works into the large value caps as designed.
David