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I Need Help With DoAll Selectron Repair

Ryanbj

Plastic
Joined
Dec 5, 2019
I recently acquired a Reid surface grinder through eBay and it has...just so many problems. Right now I'm working on fixing the mag chuck that came with the machine. It's a DoAll Selectron with a Magna Lock. The issue I'm having is that a resistor attached to one of the vacuum tubes seems to be fried. When I try to magnetize the chuck, the resistor in question turns red hot, then the circuit breaker in the Selectron trips. I'm no electrician, but I'm going to try my hand at replacing the resistor. Only problem is I can't figure out what specs are required for a replacement. The only information printed on the other resistors is "Ohmite 200Ω" and I can't seem to find an Ohmite 200ohm resistor that looks like the one I got. They are about an inch long and look like a maroon tube. The vacuum tubes these resistors are attached to are 5U4 GB, and the Selectron uses 220v 175 watts. If anyone has any ideas on what resistor I should buy your help would be much appreciated.
 

Ryanbj

Plastic
Joined
Dec 5, 2019
Have you checked the chuck windings for shorts or grounded windings.?..........resistor heating is a symptom ,not a fault in the resistor.

I did my best to check for shorts and the like but its pretty wild and 'gunky' so it's hard to be sure. However, I did remove the vacuum tube attached to the resistor and the chuck magnetized without tripping. That's my hokey attempt to isolate the problem. Also, the resistor is visibly cracked so I'm thinking it's busted. But like I said, I'm just taking stabs in the dark here so I'll keep "investigating."
 

Ryanbj

Plastic
Joined
Dec 5, 2019
Looks like an old-school wire wound power resistor. Here is one example of many like that on Ebay. Look for one similar style and size as the current one and the wattage rating will probably be similar.

TRW IRC 200 OHM 10-12 WATT NOS RESISTOR WIREWOUND METAL GLAZE CATHODE GUITAR AMP | eBay

Thank for the advice, I looked for ones that were similar and found this one Blocked
It seems to be similar size and style, so here's to hoping!
BTW, if I install a resistor with the wrong wattage rating, only the resistor will get wrecked right? Or am I jeopardizing the whole unit?
 

gustafson

Diamond
Joined
Sep 4, 2002
Location
People's Republic
Look at the size, within quality resistors the same wattage would be a similar size

If you have room, no problem with a higher wattage

Avoid the Amazon ones I have found them to not be up to their rating
 

eKretz

Diamond; Mod Squad
Joined
Mar 27, 2005
Location
Northwest Indiana, USA
Check the resistance and see if it is within spec. If it's low or shorted that would cause it to get hot. If it's correct (+/- 5% or even 10% should likely be fine), there's no need to replace it, the fault lies elsewhere.
 








 
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