Just about ready for a box of matches I think. I replaced three capacitors in the HMV fired it back up and now only have one channel working. Strange thing is the balance control also does not make any difference - all sound just coming from one channel regardless of where the balance control is positioned. There is a slight deep hum coming from the other channel, regardless of volume setting (have to put your ear to the speaker to hear it). I put the three old caps back in, and still doing it.

The only other thing I did was spray some contact cleaner (the one with light lube in it) into the volume, tone and balance pots as they were scratchy. They're not scratchy now, but!

I've checked, doubled checked everything I can see, but still the same.

Does anyone have any idea what might have happened?

Remind us what HMV model you're working on.

Sorry, my appology. It is a an N3 4Y. I just can't work out what's happened. It was working fine, just that it had one leaking cap that needed replacing and I thought might as well do the other two beside it. Thanks

Hi Clip,

I do these all the time, the moment you switched it off it blew one of the output transformers. People switch them on unrestored and they work , then on switch off they blow the transformers.

From factory they had a modified version. I use new Hammond ones to replace if you haven't got a donor.

Check the windings and you will find them open or high resistance.

Cheers
Vic

Make sure all of the valves are in their sockets properly.

Thank you folks. Yes it has a blown output transformer. Don't know why I didn't think to check that, but then that's the problem, although Ive been mucking around with old radios for 45 years, I still only know enough to get myself into trouble.

Unfortunately while I share the same genes as my great Uncle Clive Turner (who worked for Emmco in the late 1920's and designed most of the radios back then, the Troubadour being one that I remember for some reason), I don't have his brains for it.

One of the greatest mistakes & acts of foolishness, that I see constantly, is people plugging in old radios to see if they work and that's where the problems start.

Most of these sets were likely taken out of service because something failed. If not they were just put in the shed to become shelf queens. After sitting for ages, faulty or not; The electrolytic's either go open, by drying out, or loose their polarity & present as a short circuit, often resulting in an explosion.

This of course stresses the transformer as does leaking wax paper and oil filled capacitors. I have been fixing these things (and other non related things) also for over 45 years, but appreciate that there are certain procedures that one follows before even contemplating applying any form of power.

Once you have visually checked it and made sure there are no shorts from bad wire and in the case of a valve rectifier, remove it, before initially checking continuity on the HT secondary. You can test the OP transformer & speaker with a 9V battery, struck across the primary.

A valve set should never be powered with old wax paper and electrolytic capacitors in place. Rarely will you find a wax paper, or oil filled cap now that does not leak like a sieve: That leakage upsets bias & places stress on things by over current & that cooks power transformers. Some of the terminations in transformers with tabs into the wrap are mechanically unstable and can also have wire corrode off .

It would not take much expansion & contraction to trigger a fail. I did managed to repair one of those, as the issue was on top & I could get at the wire. Some insulation on the wire was not spectacular either.

Watch the methodology, as that is an area where one can fail badly.

Hum generally equals a power supply overload, often a filter cap failing. I have had a new one fail recently & there is some rubbish out their. The modern cap rarely has "peak, or surge" volts on it. Filament, Metal and Solid state rectifiers can and will cause a voltage surge that can reach twice EMF before the heater valves start conducting. On a 250VDC "B" rail I will not use less than a 500V cap with filament rectifiers like 80 / 5Y3GT.

Marc

That's good information thanks Marc, I wished you lived around the corner from me!