Good evening from a misty Mullion Cove Cornwall

I have been working on my newly acquired B44, the vibrator is a Plessey 12SR7 12 volt synchronous type.

The set purchased on eBay fired up OK, but after a few minutes the vibrator started to labour and the sound faded.

A smell of burning resister followed.

Taking the power supply out of the set revealed a very burnt 4.7k 1 watt carbon resister.

The .02mfd in parallel with it was short, replacing them restored sound but the resister would have burnt out had I left the set on.

These two are across the power supply secondary.

The circuit I have specifies a .01mfd ?

Anyway a .01 still heated the resister way too much, a .01 ceramic heated it less ? and a 5 watt wire wound ran a bit cooler.

This is obviously not right, and there is hum from the speaker as well.

Replacing the other decoupling caps .001 in the vibrator circuit and even disconnecting the feed to the receiver still does not help.

I suspect the vibrator is producing large spikes.

Update the rectifier that supplies the negative bias to the audio output valves and the PA was short circuit.

I replaced it and the two associated capacitors which were leaky, this stopped the hum

I then replaced the 1mfd across the low voltage side of the vibrator transformer, the vibrator had its can off at this time, the heating of the 4.7k appeared to stop.

I then refitted the case to the vibrator and tried again thinking all was now OK : )

The 4.7k then started heating again ?

I am fairly convinced that the vibrator has a fault, the 19set group offer a solid state replacement, but are not responding to email at the moment.

They are also not responding to a request to join the group, I only have a circuit and they have various manuals.

I did not see away to attach the circuit should it have been helpful in a reply : )

God Bless Allen G0RIT & Alanna

Do you own a serviceable 19 Set? Yes five all completre and working : )

On you tube there is a sight called Mr Carlsons Lab. He has been restoring old tube radio,s and amps. He said on one project that the old capacitors should all be changed because they leak internally and will cause the resistors to burn out, and will eventually destroy the tubes. Check out his sight you might be able to get hold of him for some advice....Hal

Do you own a serviceable 19 Set? yes