Variac hum

[William]

Today I decided to try and figure out why my home built Variac, that was given to me, produces a hum in anything I plug into it. This is something new that I discovered with my last project. Opening it up I discovered two things. One, it was full of dust and dirt. Two, the contact thing has left what looks like a carbon track on the copper wires. I'm guessing that maybe the reason for the hum and would like to start by cleaning that off but not sure what to use. Does anyone have any suggestions on what to use? Thanks in advance.

Bill

[electra225]

Can you remove the wiper? If you can, you might use fine sand paper or emery cloth and clean it up, then use a paint brush and some gentle compressed air to clean off the carbon. I don't know whether contact cleaner would harm the insulation or not.

[TC Chris]

Maybe try alcohol or DeOxit first? I always worry about plated surfaces when using abrasives. You might cure the problem temporarily but make it worse in the ling run if you grind off a conductive plating like silver on the contact portion.

Chris Campbell

[William]

Thanks, guys, all good advice.

Bill

[Conelrad]

Never use emery cloth on any contact surfaces...it is conductive, and can get between turns and cause shorts.

D

[William]

Thanks, Dennis, that is good to know.

Bill

[William]

Yesterday afternoon I tackled the Variac and I applied all suggestions. I started with some 1200 grit paper, it's what the auto store had, and lightly sanded the copper contacting part. That did a partial job but still left some embedded carbon tracking. Taking some Deoxit I sprayed a little on the clean piece of paper towel and carefully applied it to the copper. That seemed to work, and I did not see any ill effects but still was not taking enough off. Next, I took a soft, yet stiff, small brush and sprayed a dab of Deoxit onto the brush and gently scrubbed. That worked, and it pretty much removed all of the carbon tracking. I then took another clean piece of paper towel, applied a little Deoxit, and kind of gave the copper a rinse. I now have shinny looking copper. I also cleaned all other contact devices and lubed the moving parts. After assembly, I gave it a test drive with my Motorola 3 channel stereo table radio, and it seemed to be ok with no added hum. My next test will be with the VM stereo that drove me nuts trying to find the hum that led to the Variac hum problem. I'm keeping my finger crossed.

Bill

[electra225]

Not to derail your topic, but you mentioned De-Oxit. I have never had the urge to spend the extra money on De-Oxit. I always used contact cleaner, whatever was cheapest. I am beginning to rethink that. I have so much trouble with controls and switches, I'm beginning to wonder if I am penny wise, but dollar foolish not using the real stuff. I think AES handles it. What flavor of De-Oxit should I buy that will work for all kinds of contacts, including those found in TV. I assume they make different versions of De-Oxit is why I asked.

[Motorola minion]

Until the internet, in-depth effectiveness analysis of things like "Lube-a-trol" and "Tune-O-wash" were not forthcoming when those products promised the best outcomes, so I used a small can of Radio Shack tuner cleaner for everything I serviced. It lacked the lasting lubricant, DeOxit applications last far longer .

My first applications besides volume controls and AM tuning condensers were cleaning rotary-knob tuners of 70s-era color TV used on antenna: Sylvania, Magnavox GE, etc, whose marginal front-ends are so vital to pulling in all the channels without banging on top or wedging the tuner shaft.

Philco, RCA and Zenith needed the same razzle-dazzle but rarely lost MOST of the channels like most others (including most cheaper Japanese sets) did after months of use during a sport season, unfortunately this included Motorola/Quasar.

[19&41]

Not to derail your topic, but you mentioned De-Oxit. I have never had the urge to spend the extra money on De-Oxit. I always used contact cleaner, whatever was cheapest. I am beginning to rethink that. I have so much trouble with controls and switches, I'm beginning to wonder if I am penny wise, but dollar foolish not using the real stuff. I think AES handles it. What flavor of De-Oxit should I buy that will work for all kinds of contacts, including those found in TV. I assume they make different versions of De-Oxit is why I asked.

I use this one when I need a contact cleaner.


https://www.tubesandmore.com/products/d ... pray-5-24g

[William]

That's the same one I use, Rex. Somewhere back in the days of Vintage, there was a discussion about electronic cleaners, and it was decided that Deoxit was the one to use. If memory serves, I believe Chris was the one that talked up Deoxit, and provided a link that talked all about it and showed the different kinds Deoxit offers. I have multiple kinds of electronic cleaners that I use for various places within the electronic thing I might be working on. Deoxit is my usual cleaner for all pots.

Bill

[electra225]

Got it! Thanks, guys. I'll try it on the Imperial chassis. The function switch gives me fits sometimes.

[19&41]

It looks like there are some cleaners that can have an effect on the resistive elements of pots and can cause fractures in them. The DeOxit has a solvent that isn't as hard on various plastics.

[electra225]

I've been using generic contact cleaner and WD-40 on controls, really with pretty good success with the exception of the Magnavox controls and switches. I blame cad migration for the fouling of the switches and tube sockets. I need to find something that will work better. I have avoided De-Oxit because it is expensive. Do I need to use a lubricant after I use the De-Oxit?

[Ken Doyle]

I use this one when I need a contact cleaner.

https://www.tubesandmore.com/products/d ... pray-5-24g

Deoxit D5 is great for switch contacts. For potentiometers, Deoxit F5 is the correct product to use.

[19&41]

I've been using generic contact cleaner and WD-40 on controls, really with pretty good success with the exception of the Magnavox controls and switches. I blame cad migration for the fouling of the switches and tube sockets. I need to find something that will work better. I have avoided De-Oxit because it is expensive. Do I need to use a lubricant after I use the De-Oxit?

For tube sockets, I use these with 91% isopropyl alcohol. Many of the sockets on my Magnavox units used silverplated sockets. I clean with the appropriate brush, then use Dust-Off or a similar spray to clear it off. You could also apply the deoxit with one of this type brush. The one shown I use for miniature pin base sockets.

https://www.walgreens.com/store/c/g-u-m ... 23-product

[TC Chris]

On the subject of DeOxit, it's worth looking at their spec sheet (linked in the link) to learn about their other products.

I bought DeOxit in the pump dispenser, not the aerosol spray. Better control, and I can pump a bit into a container for brush application. I bought a small artist's brush for application on wafer switches and other small surfaces. Better than spraying the stuff all over and hoping the right parts get some.

Chris Campbell

[electra225]

Chris, I use your vinegar method to clean tube sockets. I like your idea of getting De-Oxit in a form that can be applied without using aerosol propulsion.