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Old 22nd January 2013, 04:45 AM   #21
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Default UPDATE

Finally got around to it. Took Xformer out, removed end bells and immersed entire unit into Polyurethane Varnish for a couple of hours.
I then let it dry out for 3 days, reassembled and reinstalled into amp.
Result? Marginally better Wasnt worth the effort nor the expense ($25 for the varnish alone)
Bummer.....
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Old 22nd January 2013, 05:45 AM   #22
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'Did tell you more appropriate methods, and a DIY version too!
There is no guarantee of any useful penetration with just 2 hours sitting in (cold?) varnish and 3 days air drying in
an enclosed volume suggests what little penetration there is could still be wet with solvent. It needs stoving to dry firm.
Hard varnishes (regular Copal, Spar varnishes etc.) are often used to ensure enough mechanical strength for impregs.
and an old transformer will need it.

Be serious, heat the transformer to 60-70 degrees C (check) first and then dip it outdoors with no ignition source or it's !
Don't remove until it is all at ambient temp. 'Not sure doing it in sub-zero weather is going to work, though.
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Old 22nd January 2013, 06:02 AM   #23
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i doubt that the windings vibrate.....

you have to shim the center leg core and the winding bobbin with wooden shims about 3/4 inch wide and 1/16 inch thick tapered at one end, if your coil is 2 inches wide, make the shim about 1 1/2 inch long, stake it in as far as it will go...take care not to hit the copper wingdings, use wooden mallets....

if you find that a 1/16 inch shim is loose, make it thicker or stake in another one on the other side....

if you are using a crs, (cold rolled steel) chassis, rubber pads under the traffo, about 1/4 inch thick can help also....
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Old 22nd January 2013, 07:31 AM   #24
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What about a failing rectifier or failing main capacitors. The failing rectifer will generate a 120 or 100 hz humm
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Old 22nd January 2013, 07:38 AM   #25
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and then the fuse blows....
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Old 22nd January 2013, 04:10 PM   #26
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Thanks guys. I`m not quite ready to give up on this as I really like the amp

Ian: if I understand correctly, I should heat the transformer and varnish first.
How long should the transfo be heated at 60c? I`m concerned about the insulation melting off the primary and secondary wires.
How would you suggest heating the varnish?
With only 1 litre of varnish to play with, the transformer would have to be "basted", would that work?

Tony: I`m not sure if there is enough clearance to accomodate wooden shims between the winds and core, if there is, can your method be used in conjunction with that of Ians?
TIA
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Old 22nd January 2013, 05:26 PM   #27
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This metyhod only gives results if the loose plates are on the outside of the transformer.
I guess the hum is from some loose ones inside the transformer and I also guess the transformer already was treated with varnish?

There should be possible to get a replacement transformer.
Theese guys will make one for You: TOROIDY.PL Transformatory Toroidalne Producent, Audio, Separacyjne, Trójfazowe, 230/110V, 110/230V, Na zamówienie
Why not?
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Old 23rd January 2013, 01:08 AM   #28
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Quote:
Originally Posted by Michael F View Post
Thanks guys. I`m not quite ready to give up on this as I really like the amp

Ian: if I understand correctly, I should heat the transformer and varnish first.
How long should the transfo be heated at 60c? I`m concerned about the insulation melting off the primary and secondary wires.
How would you suggest heating the varnish?
With only 1 litre of varnish to play with, the transformer would have to be "basted", would that work?

Tony: I`m not sure if there is enough clearance to accomodate wooden shims between the winds and core, if there is, can your method be used in conjunction with that of Ians?
TIA
you can use an oven to heat up your traffo, make sure temperature does not exceed 100*C and then you can dip your traffo in varnish....some cases needed as much as three times dipping and drying...check that your varnish is an air drying type, otherwise you need the oven to dry it....

re shimming, it may look like there's no space but shimming does help, i've seen them on american traffos that i have dismantled for rewind....try it and you may be surprised that the shim goes in....

don't give up just yet untill you have tried our suggestions....
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Old 23rd January 2013, 04:39 PM   #29
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The safety factor with the flash point of solvents used in urethane paints is potentially dangerous at 100C, in my (bucket chemist's) view. You should measure the temperature of the iron laminations, as close to the core as possible, for a truer indication of how hot the transformer really is. Don't guess - measure! I would like to use higher temperatures too, but 70-80C actual lamination temperature at the time of immersion is as high as I would venture. An important safety precaution is to do this immersion step outdoors or in a well ventilated shelter, away from ignition sources.

Transformer varnishes are only rated typically to 135C when hard, so obviously, don't set the oven above 130C. Your first attempt, if reheated, may fume and ooze a bit and if it does fume, turn the oven off, remove and let it dry out fully before reheating. It takes time to heat iron and copper up and that will depend on the total mass, the mean oven temperature and the placement, so no point guessing.

I consider any appearance of fuming dangerous, since the oven is a source of ignition when the element glows or the thermostat switches. Leave the oven door closed, but don't allow it to latch shut, if that could happen. Varnish solvent vapour, BTW, is classed as toxic. I have had my fair share of exposure to such solvents in industry and the memories are not pleasant.

With this method, room temp. varnish is used so that it cools the transformer somewhat and that enables it to be drawn into the spaces occupied by entrapped air, as that contracts. Obviously, the varnish heats up in the process, and that lowers viscosity, but the key is that the entrapped air cools. Some people do also heat the varnish but that requires real care and proper industrial plant for safety. I don't suggest any heating of varnish or drying the transformer after immersion be done at home in the kitchen oven where food is cooked.

As Tony said, it will need to be done 2 or 3 times to be fully effective, to the extent that a varnish treatment can help with buzzing laminations, anyway.
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Old 23rd January 2013, 07:53 PM   #30
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Thank you kindly for such a detailed explanation. It seems like quite the labor intensive process. I think at this point, it may be more feasable to find a new replacement transformer as I`d have to wait for warmer weather to arrive before making another attempt (-35c outside currently) to allow for proper ventilation.

Not knowing the VA rating, I just may look for the biggest 110vct transfo, torroid or conventional, that the chassis will accomodate.
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