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42-380 Issues - Printable Version

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42-380 Issues - davidff - 04-17-2015

I re-capped a 42-380 recently for a friend and replaced the rectifier tube which appeared to be weak, but working.  After a few plays, it stopped working.  All tube seem fine, I swapped the rectifier to make sure it wasn't faulty.  I read that these 6X5 tubes and the capacitors are a problem on this chassis, but would like the experts here to give me some ideas what may be the problem. 

Thanks,

RE: 42-380 Issues - morzh - 04-17-2015

What you haven't mentioned is whether after the tube swap radio started playing again.

RE: 42-380 Issues - Raleigh - 04-22-2015

Is there a reason you're suspecting the rectifier tube other than that you'd replaced it once before? It's better to do some tests before concluding it is bad, but maybe you have already.

If you don't get any sound out of the radio at all, I'd check B+ voltage before concluding the rectifier is bad. If no voltage or really low voltage, check the power transformer windings with an ohm meter. They should be somewhere near the 260 and 275 ohms on the schematic. Check the output transformer. I've heard they're a weak point because of the heat under the chassis.

Also make sure the filament voltage is good.

If power is the problem, one possibility might be the candohm bias resistor assembly. I've never had one go bad, but they have bad reputations. I've bought a couple of Philcos where they've been replaced by a previous owner.

If you get sound, (hiss, hum, etc.) but no signal, then still check B+ and tube plate voltages. If they are anywhere near correct, then start working backwards from the output stage to help localize the trouble. The 41 tube plate voltages can be 20 or 30 volts low and the radio will still play.

I have only one radio with the 6X5 rectifier, a 42-355. I play it most days with no problem. but that's only one data point.

Maybe this is just too obvious, but make sure the speaker plug is good and tight.

RE: 42-380 Issues - Arran - 04-22-2015

 On these sets the 6X5GT, in and of itself, should not be a problem. The maximum plate voltages on this set, as well as the current loads, are well bellow the maximum ratings for a 6X5 tube, the plate voltage is somewhere around 180 vdc, and the set uses #41s which are the same as a 6K6 electrically. Can 6X5s wear out, yes, but in spite of the hysteria they are not the spawn of Satan that the ARF crowd carries on about if they are used correctly, and not incorrectly as in one of their saintly order of the big black dial sets. Now the output transformers are a known weak point in these sets, in fact in most 1939-42 Philcos with push pull output tubes, so check that.
Regards
Arran