Rusty Murphy A48 chassis

[PJL]

I would avoid too much varnish and use just enough to stop the cores falling apart further. I assume wax was used on coils for a reason as it allows for some expansion/contraction. Test them first as you only need to replace the wax if they still work!

[audion_1908]

I will let the IF cans dry out for longer before I work on them, but I have found something strange, the murphy service manual lists C47 the first electronic smoothing capacitor as being 8uf or 16uf in the A48RG model, the badly faded electronic can had 8 - 8uf printed on it and both the pins where solder together, I looked up the A48RG model and it's a radio gram!

so it looks like I will have to order some more 1uf 630v film capacitors, I know it will work with only 8uf

[audion_1908]

The murphy service manual for the A48 lists the rectifier as a UU4, but a UU5 is fitted, the data sheet for them tells me they are about the same but the UU5 is rated at a higher voltage but same current and 8uf max reservoir condenser?

[MurphyNut]

As you haven't replied to my PM, I'll post the requested pictures here. I needed to take the chassis out of the cabinet of my A48 anyway to sort out the crackling wave change and volume controls. Hope the pictures are helpful.

[robin coleman]

I saw this set on a sale site but did not get it.I too was up for a challenge hope you get it working soon.
Regards
Robin

[audion_1908]

It's been a wile but I am back working on the Murphy A48 chassis agen, I have soaked the crumbling rusty iron dust IF cores in indoor outdoor wood vanish to hopefully mechanicy stables them, it was a surprise how much varnish they took! I also used PVA to fix some of the lose paper on the transformer, I then put 3 layers of brown paper on each side, it's funny I was looking out for brown paper that was the best match color wise, and not waxed, then I realized brown bill envelopes where just what I needed!

[audion_1908]

The transformer dose not look like it was waxed or vanished before I put the chassis in the dishwasher? If it was a valuable or rare radio chassis I would have removed the transformer and IF coils first, but it was already very water damaged, here are the pics of the transformer with the new paper, I will vanish it in a few days when the PVA is completely dry.

Link to old thread
https://www.vintage-radio.net/forum/...d.php?t=138049

[Boater Sam]

Are you just varnishing for appearance or insulation?
I have re-impregnated many transformers by warming them to around 50C and dipping them in varnish. As they cool, the varnish is drawn into the windings and core, they run silently afterwards and it keeps the damp out.
It would need to be totally free of moisture first of course, a week in the airing cupboard before dipping would be good.

[audion_1908]

I am varnishing the IF coils for mechanical strength, and the transformer for mechanical and electrical strength, I was planning to pore the vanish in with a teaspoon, I know it's not ideal, I am thinking about dipping it but am not shore it's worth the effort of getting the rusted up bolts off and removing all the brittle wires, also all my wood varnish is in little tins from the £1 shop, I will have to look and see if I have enough.
Did you use wood varnish?

[audion_1908]

Thanks admin for fixing the new to my old thread!

[audion_1908]

Originally Posted by Boater Sam

Are you just varnishing for appearance or insulation?
I have re-impregnated many transformers by warming them to around 50C and dipping them in varnish. As they cool, the varnish is drawn into the windings and core, they run silently afterwards and it keeps the damp out.
It would need to be totally free of moisture first of course, a week in the airing cupboard before dipping would be good.

Can you tell me more about the proses, like how long to bake for and how long you dip the transformer? Thanks

[Radio Tech]

I think for certain that you have you work cut out restoring this set to its former glory, and certainly it shows how enthusiastic you must be to take on such a challenge as you have suggested, the chemicals used in the dish washer certainly shifted a lot of the dirt and some rust but I feel in the end it will be like giving gold to someone for copper in return. The coils and slugs will almost be shot. But, none the less, good luck with this huge project.

Ken

[Boater Sam]

I warm the whole transformer up and dip for a minute or so, hang up to drip and cool down. When cold, its done.
If you can't dip, a good coating with a brush will do but its messier. Avoid the fumes of warm varnish if its a high VOC.

[audion_1908]

Thanks, fixing this radio is for the challenge, not so much the result, and I plan to build a depression era tomestone or cathedral wooden case for it, I have got a signal generator to test it when I have all the basic problems fixed, the IF cores look solid now! I will test them for continuity next, I also have a component tester that may be able to test the IF core inductence, and can definitely test the open mica capasters if they are still good

I bort some more varnish, so should be able to dip it, I am lucky my oven is easy to set to 50c

[audion_1908]

I have done a quick test on the IF coils 3 test ok, the 3rd is sadly open, I will test all the coils inductence and the capasters when I find a 9v battery for the meter.