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Old 18th Dec 2018, 5:42 am   #46
Catkins
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Join Date: Feb 2015
Location: Chepstow, Monmouthshire, UK.
Posts: 234
Default Re: 1938 Murphy A56V television restoration

PSU restoration Part 2

That corroded EHT winding wire proved to be a major problem. I tried soldering a wire to it, but of course, being corroded the solder wouldn't stick (but it was worth a try). I tried cleaning the wire, and the inevitable happened, it snapped off clean to where it emerged from the transformer

At this point there seemed very little option but to send it to Mike Barker for rewinding. But then something unexpected came to the rescue.

Wax. The EHT transformer windings are heavily impregnated with wax, and there was a layer of wax on top of the transformer. Melting away the wax revealed about 3mm of uncorroded EHT winding wire. I managed to successfully attach a wire to that.

I stripped the EHT transformer down, de-rusted the metal assemblies and repainted. I stripped the EHT circuit (rectifier and bleeders) off the paxolin board, cleaned and glued it (where the hair-line cracks were) to strengthen it. I then rebuilt the EHT circuit with new components., as they were all open-circuit.

Finally I stripped down, de-rusted and repainted the chokes. Then I put it all back together with mostly new wire (the systoflex covering was mostly OK and didn't need replacing).

Photo 1 shows a photo of the unrestored mains transformer, because I didn't have room in the previous post.

Photo 2 shows some of the treated metal assemblies on the EHT transformer.

Photo 3 shows the stripped down, and restored paxolin board,

Photo 4 shows the rebuilt EHT circuit on the paxolin board.

Photo 5 shows the underside of the finished PSU.
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