37-62: rectifier and power tubes swapped - Printable Version

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37-62: rectifier and power tubes swapped - stevenmatthew - 10-06-2023

I picked up a working 37-62 (tabletop with photofinish) from an elderly lady on Craigslist. She said it had been in her family for a few generations, but nobody seemed to want it any longer. She also said that it still worked, so I drove the two hours to pick it up. When I arrived, the lady told me that she had her grandson clean it up a bit for me. Apparently he had used a mild abrasive powder, because the photofinish decal had a number of small scratches on it. The chassis, however, appeared clean. The kid had obviously wiped down the tubes and blow/vacuumed out the dust.

Since it was in relatively good shape, I was eager to recap and get it playing. I restuffed the caps in the original cans and aluminum tubes, and had the job finished the following evening. Everything looked good, so I plugged it into the varic and slowly raised the voltage. As I approved 100V, there was a snapping sound and a puff of stinky black smoke. ARRRRGH! I spent the next hour trying to figure out whether I had mistakenly placed the caps in the wrong locations, had used the wrong values, or had accidentally introduced a short. It appeared as though everything was correct, so I replaced the blown cap in question and brought it up to working voltage without success.

I attached a signal generator to the antenna and was able to trace the signal up to the cap of the 6A8, though I got nothing beyond it. I also tested the speaker and was relieved to hear a tone through the transformer. While I was swapping out the tubes, I noticed that the rectifier tube was not hot (or even warm). When I pulled the tube out to inspect it, I found that the rectifier and output tubes had been inserted into the wrong sockets. Apparently when the lady (or the kid, more likely) had cleaned it up, they had put the tubes back in the wrong order and I had failed to verify that everything was in the right place before turning it on.

I swapped out the rectifier and output tubes, but I'm still not getting anything out of it. I'm unsure whether the tubes I swapped in were any good, or perhaps there's more damage that I haven't yet found. I can usually attach my RF signal tracer to either the tuning capacitor or the cap of the RF tube/detector and adjust the tuner until I get the nearest station (only a few miles away, so it comes in loud n' clear without an external antenna). This isn't the case this time. That said, I CAN get the tones from my signal generator at the tube's cap, so I'm confident that the antenna coil itself isn't burned. Not sure what to make of this.

I can get 6.5 volts out of the heaters for all the tubes, but I'm not getting any DC anywhere on the rectifier. I have a tube tester, but it's not one of the fancy-schmancy Hickocks, so I doubt whatever it tells me. I have a few other radios lying around, but nothing that uses a similar set of tubes, so I'm unable to swap them out to eliminate the ones with damage. So: aside from ordering an entirely new set of tubes (which cost me more than I paid for the radio), can anyone suggest where/how to begin troubleshooting? This is the first time I've ever encountered a situation where the tubes were in the wrong sockets, so I'm not sure what manner of damage this did, or how to determine the extent of it.

The schematic can be found here: Schematic

Any suggestions are appreciated!

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