I have had a significant number of Valve equipment power transformers fail over the years due to shorted turns…simply because there are so many turns of fine wire at so few volts per turn at mains frequencies….also had a 950v secondary in a Gould 4035 Oscilloscope that supplies the tube have shorted turns….enough to cause a 200w globe to glow about a quarter bright and a hot smell to eminate from the transformer. In that case I unwound the 6.3v tube heater winding and the 950v was the next winding down…got right “medieval” on it and chomped half of it away…put loads of captan tape over it, rewound the 6.3 on top and voltage doubled off what was left…which was about 415v worth….it worked quite well for about eight months then shorted again. this time I’m ripping it sll off and replacing it with a 25v winding to drive a Royer or Flyback ferrire vored EHT supply for the tube. Do have some valve regulated HV supplies here, two from Sanborn electromedical equioment….but both with just 120v primaries and a multitude of 350v secondaries…two driving a 5U4 locally, but the others went through wiring looms to remote rectifiers in the huge Sanborn 350 racks. As I’m in Australia, I will series the two 120v primaries on the two transformers, then parallel all the 350v secondaries between each to get them to share the load equally so I can run them of our 240v mains. They use 6L6’s as pass regs, 85A2’s as references and 12AT7’s as diff amps. Here, I would pull ALL the valves…including the 5U4 and jst see what the transformer draws on its own with no loads at all. the 5U4 heater draws 3A at 5v, so there is 15W already. When you showed the ripple, every second half cycle looked lower, suggesting a higher source impedance in one of the 5U4’s anodes than the other. I’d be loading down those secondaries with strings of low powered light globes….don’t you have 7.5w, 115v candle lampe over there in the United States? Put four of those in series to get a 30W, 500v resultant load you can test the secondaries wiith…form one end to the centre tap of course, not right across the whole lot. Somewhere I saw a video of a fellow Aussie getting the power transformer of a late 1920’s AWA (Our equivalent of your RCA) TRF radio rewound…yep here it is… nCB-iEllFak. He did happen to know a guy who would tacetly rewind transformers but did not openly advertise the fact. This is certainly a project I would like to complete too…do have a PS from a transmitter that has two 866A’s and two or three 5U4’s followed by regulators…..about four supplies in all of two transformers…and quite a few chokes and oil filled caps with bushings and dodgey dielectric inside….could tuen that into a HV bench supply, but a lot of work to make it safe and goof proof around the terminals!

You stated that this power supply has a full wave bridge rectifier configuration, and you also claim it has 60 Hz ripple, those 2 things do not add up ( it should be 120Hz ripple), something is still faulty or miswired. I would load test that transformer for its AC output without the circuitry before condemning it. The small "transformer" you pointed to on the bottom of the chassis is most likely a choke inline with the output, if that is shorted it will not remove the last of the ripple as well.

To paraphrase: "I've done everything right and it still doesn't work". I don't think your power transformer is bad; transformers don't just start delivering low current. I recommend getting a schematic for the A3A and carefully checking ALL your work. If a rectifier is getting hot then possibly too much current is going through it. With the wrong tube installed (6SH7), it may have been modified; the correct tube may now be a mistake, and other parts may have been changed. BTW, I'm a tech.

Send to Mr Carlson I bet he will fix it :D

🙌🏼

Possible leakage from potentiometer/switch casings, wiring, or from the meter already eliminated as a possible fault source? I remember I recently had quite some "fun" fixing an analog multimeter where there was leakage (not even high voltage leakage, it ended up putting the ohms battery in circuit at unexpected times) from movement to meter face to meter mounting screws through some degraded electrical tape below the meter face to the battery contacts.... I'd be tempted to have at every front panel control that is still connected to anything with just the rectifier in with an insulation tester...

Don't give up. Swap in a different transformer from an old radio chassis. Transformers are not critical. You can re-wind that one, too.