Variac brush problem.

Thread Starter

thedoc8

Joined Nov 28, 2012
153
I have a powerstat 1156b variac. The brush seems to be froze in the fixture. Does anyone know how the brush assembly is attached. The two screws on the front keep the tension on the brushes, got the two screws out and don't see how to remove the assembly and don't want to break, 179 buck for a replacement. I have included 2 pictures. Thanks much to anyone that can help.
 

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Looks like that cartridge should be free with those two screws loose. I would suggest some penetrating oil like Kano Kroil, etc. as a first approach - apply a little bit to the joints and let it sit overnight to try to dissolve whatever residual oils have gummed up inside of there. Failing that, some careful hits using a soft aluminum rod as a punch against the brass might do the trick. I'd reserve heat as a last resort - by removing the wiper plate, cleaning all combustible residues off of it and carefully warming the aluminum with a distant torch flame. The differential expansion rates of the aluminum and brass might be enough to crack it loose and/or soften the gum inside of there.
 

ericgibbs

Joined Jan 29, 2010
11,628
hi,
It looks as though the windings at the point of contact with the wiper brush assembly have over heated.
It was held in place by solder flooding of the two retaining holes, the solder bond has now melted and the wiper brush appears to be 'fused' to the transformer winding.
E
 

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Alec_t

Joined Sep 17, 2013
11,801
I'd try a hot air gun on it, combined with a bit of leverage on the copper block.
Is it a camera artifact, or are the winding turns on the right-hand side in your second pic damaged?
 

jpanhalt

Joined Jan 18, 2008
10,953
My oldest Variac was made by General Radio in Cambridge, Mass. before ZIP codes were invented. It is strictly 2-wire, and I had to replace the power cord recently. The internal wires to supply were surprisingly short, but it now works as well as new.

1) I would not pry or force anything until I had good visual confirmation of what was being pried or forced. Nothing in the pictures shows why the contact will not move.
2) I would carefully disassemble until I got to that point. By careful, I include marking orientations and screws such that they can be replaced as closely as possible to original. Fine tipped permanent markers work well. Nothing posted here shows that degree of disassembly.
 

Thread Starter

thedoc8

Joined Nov 28, 2012
153
Though I replied to this, but thanks to all again. The variac was fine no overheat. Turns out just had to wiggle it a little harder and lightly clean its mounting. The brush had one small nick. The company is still in business as most of you already know. The new brush from the co. was 99 bucks or send it in (the brush) and they will rebuild it for about 40 bucks. Thats not bad.
 
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