has anyone got any tips as to how to deal with these? Some of the pots and rotary switches I come across seem (at first sight at any rate) to be fully encased and consequently very difficult (and some) to get any lubricant into. I reckon there must be some old trick or knack I'm not familiar with. Is there any alternative to removing them outright and soaking them or drilling tiny holes in the casings to squirt lube in through?
I have this wonderful little device made from a bit of brass tubing, a thre aded fitting soldered onto it and a small piston that seals with O-rings - almost like a very primitive syringe.
How it works: The threaded fitting has a small O-ring inside and is threade d onto the switch or pot until it seals. Lubricant is introduced and the pi ston inserted. By activating the piston, the lubricant is then forced arou nd the shaft into the guts of the pot or switch.
Works like a charm. The tube is a few inches long to accommodate different shaft lengths, but one does not have to fill the thing. The piston (if made correctly) seals the tube so that the lubricant is directed into the pot. The pot just needs to face UP.
Peter Wieck Melrose Park, PA
What thread are you talking about here? The one the shaft revolves inside of that's used for securing the pot/switch to the front panel?? Can't see how that would work. :-/
Consider the simple case - a hollow tube, with inside threads that match those around the outside of the pot's bushing (the one you screw the retaining nut onto). Screw this on, hold the pot with the tube pointing upwards, and pour or spray a suitable cleaning solution into the top of the tube. It flows down, and surrounds the pot's shaft (which comes out through the bushing).
The shaft is not hermetically sealed to the bushing - it can't be. There's always going to be a small gap between the outside of the shaft, and the inside of the bushing... and the cleaning solution can flow through this gap and into the inside of the pot.
For a "fully sealed" pot, this gap's going to be quite small - there may be an O-ring seal inside, I suppose. So, you may need to pressurize the cleaning solution to force it into the pot. That can be done by forcing a piston of some sort into the tube, or by attaching a syringe to the top of the tube (via a sealed cap) and squirting/pressurizing that way, or etc.
A guy named Bill Turner used to sell an injection tool of that sort, and also sold oleic acid (which can be diluted in naptha to create something a bit like the original Cramolin Red contact cleaner). I don't think he's still in business, though.
** Drilling a small hole is your safest bet.
It always works and will not remove the grease packed into the shaft bearing and ruin the control's nice feel as with the other idea posted here.
FYI;
just serviced some early 60s UK made valve audio that used fully sealed, ganged pots for volume, balance, bass & treble.
Not a sign of noise in any of them.
.... Phil
Someone else now has the domain name for Turner's website.
-- Never piss off an Engineer! They don't get mad. They don't get even. They go for over unity! ;-)
Bill's health was always been nebulous since he started on the web. I thin k he's still alive, but with his eyesight being what it is and other health issues, he had to give up the hobby. Too bad. A very innovative guy who sold wares for barely more than it cost him, and he gave his knowledge free ly.
Sometimes I use the red nozzle against seams, and often gets inside enough to do the job. Sprays have them, WD40, CRC 2-26, Deoxit. A little alcohol or naphtha mixed with oleic acid gets into cracks.
Greg
What make? Can reliability be assumed for any make?
Back in 1972 I bought a Ferrograph 307Mkii amp. Very good machine for the time, but after 18 months I had to replace the volume control (concentric pots) as it had become noisy on rotation. A few years later in 1976 I bought a really cheap Hong Kong made LW/MW/VHF transistor radio. Within a year the wave-change switch was very unreliable despite not being used much. But, the on/off-volume control has been perfect for over 40 years. I reckon I've turned that radio on/off, and rotated that pot, over 15000 times during that period.
-- Jeff
Some controls can be made noisy by a leak of DC from somewhere. Bad Caps?
-- Adrian C
** Made in the UK, in the early 60s, installed in a Rogers Cadet 2 stereo pre-amp.
Exceptional longevity in service is the result of very good design, not some half baked notion called "reliability".
.... Phil
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