This Westinghouse AM radio will sometimes play and sometimes not. When it plays, it sounds great. When it doesn't, I hear static (not a constant hum or buzz).

I have replaced the electrolytic filter capacitors along with the capacitor that grounds one side of the AC line. I thought the problem was due to cold solder connections, but the problem still continues.

When the radio doesn't play, I notice the plate voltage on the converter, IF amp, and detector drop about 5-10 Volts. I traced back to the filter cap, and it's Voltage drops (from 98 to 93V), which tells me there is a short circuit somewhere. I'm thinking the problem is within the RC network between the detector and audio output. Any ideas? Thanks!

Mark, I assume you've recapped this radio?

I couldn't find a schematic for this set. But I assume it's a post-war set with 1" square I.F. xmfrs? If so, then I would suspect the "silver mica disease" for one of the IFs.

If this is the problem, you can do a Google search and come up with several fixes, none of which are exactly my idea of fun. Perhaps somebody here will propose their favorite fix.

I'm not aware of a source for replacement 455-kHz IF xfmrs suitable for tube-type radios. You can always canabalize a replacement from a junker set.

I've only replaced the three capacitors I described in my original post. All others are original. If one of the IF can capacitors opened, I don't see how this would cause the plate voltage to drop.

:Mark, I assume you've recapped this radio?
:
:I couldn't find a schematic for this set. But I assume it's a post-war set with 1" square I.F. xmfrs? If so, then I would suspect the "silver mica disease" for one of the IFs.
:
:If this is the problem, you can do a Google search and come up with several fixes, none of which are exactly my idea of fun. Perhaps somebody here will propose their favorite fix.
:
:I'm not aware of a source for replacement 455-kHz IF xfmrs suitable for tube-type radios. You can always canabalize a replacement from a junker set.

I would replace all the remaining caps, one by one, retesting the radio after each one is replaced -- to be sure you haven't introduced a new problem by miswiring.

The silver mica migration doesn't "open" a cap in an IF xfmr - it shorts between the two caps, primary and secondary. This puts some or all of the B+ voltage on the next tube's grid, which can cause loud static. I can see how this would increase the plate current and, thus, reduce the plate voltage.

:I would replace all the remaining caps, one by one, retesting the radio after each one is replaced -- to be sure you haven't introduced a new problem by miswiring.
:
:The silver mica migration doesn't "open" a cap in an IF xfmr - it shorts between the two caps, primary and secondary. This puts some or all of the B+ voltage on the next tube's grid, which can cause loud static. I can see how this would increase the plate current and, thus, reduce the plate voltage.

Guys,

There is a schematic for this radio at http://techpreservation.dyndns.org/schematics/manufacturer.htm. Just select Westinghouse and under model select V-2184-1. The file is in djvu format. Is also listed in Photofact 211-17.

Radiodoc

If the trimmers are mounted on a porcelain form, and are separate from eachother (on opposite ends), and the porcelain is not dirty, then you do not likely have trouble here. If you wish to test the IF coils, disconnect the coils from the trimmers (open the can carefully). Check resistances with coils connected and disconnected. I think that this is a rare problem. I have never had trouble with trimmers mounted per above, and I have a lot of radios with this configuration. It would take a lot of dirt on the porcelain to cause an arc. I have had more problem where permanent condensers are molded in the plastic bases of IF transformers in 1950s radios.

Your problem is more likely a shorted condenser under the chassis. I would strongly suggest looking here, first. If you ever do get shorts with the porcelain form mounted trimmers, it is usually a short across each trimmer, which would short out each coil, not between the coils. Another problem would be with the trimmer screw insulation breaking down. If the screw touched the can, this would cause a B+ short. If wires within the can shorted against the can, this would short out the B+. Better radios have paper insulators within the can. An easy test for shorts to the can is to remove all IF wires from tube sockets, etc., and then check for continuity between these wires and the can (or chassis).

Occasionally trimmers become gummy with cigarette smoke residue or something else. This can cause poor reception. Disassembly and cleaning, or a good spraying with tuner cleaner (trimmers removed from can) will cure the problem. If you decide not to disassemble the trimmers, and want to wash them with tuner cleaner, open the trimmers up as far as possible (remove screw). Spray and allow to dry. Do not dry in an oven or you'll melt the coil wax. You'll have to realign the radio after this. If you are hasty and don't allow your trimmers to dry, you'll have irratic results. If you can get the radio to play at all, tuning will be thrown off as the trimmers dry. With tuner cleaner, though, evaporation is quite rapid.

I still really think that your trouble is not in the IF cans at all.

Thomas

Thomas, the silver disease I'm talking about occurs with 1950s-era IFs that are mounted on a plastic coil form - no ceramic is involved, at least on the ones I've encountered problems with. There are two adjustable silver-mica caps that share a small, common piece of mica. The silver can creep across the gap between the two silvered patches, shorting the primary to secondary.

Although I suspect the silver mica disease in one of the IFs, I certainly agree that the first order of business should be to replace all the caps under the chassis. Hopefully, that will fix it, but I wouldn't bet on it.

Ah, yes, 1950s IF transformers. How troublesome they are. Well, now that we have that settled, I must say that I agree with you 100%. Those little buggers can be a real problem. The problem is not that common, but it does happen from time to time with these units, and when it happens, it makes troubleshooting difficult.

Thomas

Sorry, I misspoke. The type of IF I'm talking about has fixed caps (which are subject to the disease) and coils with adjustable slugs.

The fix I've followed is to remove the guts from the can, disconnect the caps, and replace with new silver-mica or ceramic (NPO) caps (mounted either inside the can or hanging below the chassis). It sounds easier than it really is because the original wire you're dealing with is very fine.

I've read of another fix that I want to try next time. This involves running a drill bit through the plastic xfmr form so as to physically separate the two halves of the mica substate.

Yep, I'm talking about the fixed kind. I melt through the plastic with my soldering iron, and then I rip the guts apart. You could use a drill. I can see this as a good alternative. Then I use a new condenser in place of the old one. Ideally the new one should be the same value as the old one, but an approximation usually works. One radio I did this to had INCREDIBLE sensitivity once I was done.

Thomas

Mark, I think the consensus is that you should go ahead and replace the remaining caps under the chassis, particularly any paper caps. There's a chance that will cure the problem, but if not then you can then look at the possible problem with an IF xfmr.

Thanks Doug! I'll keep you posted. Seems it's always the component I didn't check!

:Mark, I think the consensus is that you should go ahead and replace the remaining caps under the chassis, particularly any paper caps. There's a chance that will cure the problem, but if not then you can then look at the possible problem with an IF xfmr.