Oregon Electric A3A Restoration Failure MASSIVE BER (Beyond Economic Repair)

A huge thank you again for all that continue to Join us in the lab for repairs and alignments. The channel would not exist with out all of you so thank you again for dropping by.
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In this video, we dive into the ambitious project of building a vacuum tube power supply, only to encounter unexpected hurdles and, ultimately, failure. Join us as we explore the highs and lows of tinkering with vintage technology, offering valuable insights and lessons learned along the way. If you're a fellow enthusiast or simply curious about the trials of DIY electronics, this cautionary tale might just save you from a similar fate! Watch now for a rollercoaster ride through the world of vacuum tube experimentation gone wrong.
** Repair exposes the Tech to mains electric and should only be done by trained personnel. Errors can be fatal. **

[@poormanselectronicsbench2021]

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.

[@Joseph-ut4ui]

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.

[@hughgilbert390]

The yellow wires (heater?) appear to go to pins 2,7 of the 6sh7 pentode so I don't believe a 6sn7 dual triode will work there. They have completely different base diagrams.

[@poormanselectronicsbench2021]

The 'changed tube" thing is a very valid issue in a lot of old gear. I have seen old shortwave radios where someone probably read an article in a Ham radio magazine to "make your radio better" , tried to make some tube and wiring changes, probably failed, and either gave up or if it did work better, never made any notes inside the radio that something was changed. Whenever finding an improper tube in a device, its best to either compare wiring and associated components to a schematic, or if a schematic isn't available, at least get the datasheets for the tubes you've found, and what should be installed, and then root around to see what is proper, or what might be needed to be corrected.

[@splitprissm9339]

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...

[@jenniferwhitewolf3784]

I can't believe the small size of the filter caps. I built a variac adjusted 0 to +1,200 supply for my lab and used many hundreds of uF, and included a bleeder system. Yes, it is has plenty lethal potential and joules of storage, so caution is necessary... but such is the case with 304TLs.

[@ZenwizardStudios]

This is usually due to the vacuum tube rectifier the capacitance needs to be limited because of inrush current. The rectifier tube is rated for a specific capacitance on the far side. If this is exceeded but to much the inrush current at start up can turn the cathode of the rectifier in to a fuse and melt the bonding wire.

[@jenniferwhitewolf3784]

@@ZenwizardStudiosThe current is limited by use of an inductor that has both DC resistance, and AC impedance, thus limiting the charge current of following caps at haversine peak. If you don’t use a properly selected inductance, one must use a resistor post tube rectifier, and even with silicon. We use a Tek clamp on current probe to monitor the current waveform very carefully when designing power supplies. Managing peak currents at haversine is rarely done, but essential to ensure long life by never having over spec currents for even a uS of waveform period.

[@thanhhuynh272]

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!

[@thatampguy]

🙌🏼

[@ViniciusMiguel1988]

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

[@jenniferwhitewolf3784]

Why not just gut their circuits and obtain a few new transformers, and design your own pass regs..

[@jerrymalone8370]

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.

[@splitprissm9339]

My approach would be to take the transformer out, and measure it through on a variac (probably, one could get the secondary to the right voltage to drive some light light bulbs or power resistors). And get out the thermal camera, the current probes, and the insulation tester (which probably is a good idea to use on a potentially damaged transformer anyway, esp if it is in a high voltage PSU that can float - if the positive gets grounded accidentally, you could end up with minus a couple hundred volts extra hammering on the primary/secondary insulation). Doubt any radio chassis that would be ok to junk has a remotely suitable transformer anyway though - you'd probably be looking for a junk-able guitar amplifier or transmitter....