[NJARC] This Weekend!- Thanks!

[Scott Roberts]

I wanted to thank John & Steve for their most useful help with working on the radios this past weekend at Info Age. 

The final report is that there is no problem with the BC-348Q(Uncle Bill's set, which I reworked back to original wiring and added a power supply in place of original replacement for the dynamotor a few years back)- it was simply an impedance issue with the speaker: hooked up through a transformer in a signal tracer, it worked very nicely.

The HT-37(which I worked on while assisting John) has its newly rewound transformer almost completely hooked up, and a few suggestions were accepted regarding replacing a few electrolytics I had overlooked previously. Not on line yet, but nearer, by far, than yesterday morning.

The SX-16, which has long had a BFO issue, and more recently an output issue, had the latter cured the same way as the BC-348. 

The BFO proved a much more able combatant- John worked the problem for several hours, including loosening the BFO subchassis, and removing the cover from the BFO transformer can. He checked everything, and after many hours, started laughing out loud. Seems there was a misplaced wire- the heater supply wire, which had gotten tucked up inside the subchassis box when I was reassembling it to the chassis when I did pretty much the same things John did, although John knew what he was doing... lol... Anyway, the lead connected, the BFO issue remained- No BFO when switched on, although numbers were better. So he turned to the BFO pot. Hooking another in place parallel with the other, the numbers came within spec, although the BFO still failed to operate. So we closed it up around midnight, and headed home after trying a tube substitution. John advised me to try removing the original pot, and put in a test one, as he had not removed it fully from the circuit,
 etc.

Anyway, I pulled the BFO pot out tonight: I disassembled it(as advised by John) and found the construction "unusual" by my experience: Instead of the normal wraps of wire and a rotating wiper, it has a pair of concentric rings: the outer a carbon ring, the inner stainless steel. A rotating wiper pushed the inner ring out against the outer one, leading to contact as it rotated, giving the change of resistance based on position. Anyway, the inner ring had crud on the contact face, so I cleaned it gently. Then I tested the continuity between the ends, and then each end & center. 

There was no continuity between the ends. However, the center terminal shows continuity between one end all the way to the other. There is no continuity at all form the other end to the center at any point. So, it appears the resistance section has an open. I am now going to put another pot in place, and see how it works. I have a few NOS audio tapers in stock, and even had a couple .5M, which is what is required.

Hope this fixes it!

Thanks again to John and Steve! Hope we can get together again in the next month or so, and get a few other things hammered out. I should have a report by the next meeting :)

Scott