I finally got my 38-7 working good, and now I'm trying to do the same with an 89L. With this one I'm not getting anything except a very low volume hum from the speaker regardless of volume, band, etc. All tubes are lit and I replaced both electrolytics and a corroded wire, but still nothing. I dont see any other paper capicitors in this chassis ( the 38-7 had a bunch. I haven't tested all resistors yet, but was wondering what all could cause this problem. Could it be a broken IF transformer coil?
Where should I start with this? Thanks
Mike

If you touch the high or center terminal of the volume control with the control turned all the way up, do you get a hum in the speaker? If you do, then your trouble is most likely not in the audio section, but rather in the RF section. If this is the case, you may have an open coil. Otherwise check below.

The problem you have could be due to many things. First, be sure that all capacitors are NOT leaky at all (not even in the millions of ohms). Any leakage will cause distortion. A short might cut out audio all together. Second, check all resistors for opens and drifting. If anything, your problem is most likely due to an open, though drifting over 20% can cause trouble in some cases....especially in power circuits (cathode bias, B+, etc., though not necessarily in the plate circuit of primary audio tubes...that is rather flexible).

If you cannot find trouble in those areas, start checking voltages. You could have a broken or missing wire. You could also have a faulty tube, where either a grid is shorted, or a primary element (cathode or plate) has an open connection (cathode connection strips have been known to fuse open). You could also have an open output transformer. If the hum is very faint, it could be hum induced from the field coil. You could also have a shorted tone capacitor across the output primary, or somewhere else in the audio circuit.

Thomas

I scored a Philco 7050 tube tester locally on ebay for $17.50 which really made my day today. I tested all tubes and got indications of Shorts in the 44 RF tube, and the 36 DET&OSC tube. Maybe this could be part of my problem? Anyway while I'm waiting on replacements I will check all resistors and look for bad wires. Thanks for the help Thomas.
Mike

On what elements are the shorts indicated?

Thomas

One was on B the other was on B and C. I just went to test them again to double check which was which, and now the "Short" light is not staying lit with either tube. Before it was staying lit and/or continuously flickering on these elements. Maybe the tubes are good then. I don't know much about testers so I'm kind of confused about the inconsistency here.
Mike

What is B and C?

T.

Those are the Switch positions that were showing shorts on the tube tester. I've tested them since though and now they are testing good. I'm wondering if some dust or something in the tester could have caused a false short reading on the bulb. I think I will test for voltage at the test points on the schematic, and then test resistors for openings or out of tolerance. I'm going on the assumption though that the tubes are actually good.
Mike