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42-355 B+ Tolerance
#2

Update. I looked around for wiring errors, and found that I had forgotten to reinstall the triode plate load resistor for the XXFM (part 79). I put that part in and remeasured the plate voltages again. All were 10-25 volts low, except the oscillator tube, which was about 50 volts high. There was no voltage drop across the plate load resistor for the oscillator, so I figured the oscillator wasn't working. I replaced the oscillator XXL, and the radio started to work, but the plate voltage on the oscillator was still way too high. I played around with different oscillator tubes, and discovered the tubes were not making good contact to the socket. I cleaned the socket and solved that problem. No change in the oscillator plate voltage, though.

I replaced the candohm resistor strip with modern discrete resistors. When I removed the original, it measured out OK, but for some reason the oscillator plate voltage is now a little bit low, the same as all the other tubes.

I get good reception on all bands. I even get strong reception on FM, picking up stations from the bottom half of the modern FM band at about 1/2 of their actual frequency. I don't know how this happens, but it seems to work.

I aligned the AM and SW bands, and now I get good strong reception everywhere. I decided not to touch the FM alignment, since the instructions are confusing, and since I mysteriously get good reception on that band. However, when I set up the AM push button coils and compensators, some of the stations on the push buttons came out MUCH stronger than when I tuned those same stations on the dial, others not. I'm really not sure why this should happen. Maybe the antenna compensator for the broadcast band? When I turn that compensator, not much happens.

John Honeycutt


Messages In This Thread
42-355 B+ Tolerance - by Raleigh - 09-01-2009, 11:56 AM
Re: 42-355 B+ Tolerance - by Raleigh - 09-08-2009, 06:40 PM



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