NOS Wire-wound potentiometer mold cleaning question

Discussion in '"Boat Anchor" & Classic Equipment' started by N2RDQ, Oct 16, 2018.

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  1. N2RDQ

    N2RDQ Ham Member QRZ Page

    I'm looking to clean this very old NOS wire-wound Clarostat RA30 pot. it appears like there is mold on the wire-wound resistor cause it's white and stringy under a microscope. It appears like the wire wound part is wound around a phelonic pcb substrate. its old enough also any lube has turned to wax.

    doing some research it seems that the wire wound resistor is wound around material made up of Phenol-formaldehyde which is degraded by the white rot fungus Phanerochaete chrysosporium. I'm positive this is exactly what I am seeing here. I will say this is the first seeing this on phenolic, but, seeing that the whole unit this pot is going into is also made of phenolic pcb's id hate to see this mold get into the rest of the unit.

    Looking for how to cleaning this pot without damaging the phenolic or the bakelite, and how to properly lubricate it, and where to lubricate it, should i lube jsut the shaft or should there be any lube on the wiper area? Also looking to keep this issue from coming back, or even worse spreading to any other phenolic in the equipment its in.
  2. WD0GOF

    WD0GOF Ham Member QRZ Page

    There are only two things that I know of that will totally eradicate mold or Fungi, Chlorine bleach or sulfur alkaloids. You may want to research those.

    I would not lube the wiper.
  3. W2WDX

    W2WDX Premium Subscriber QRZ Page

    P. chrysosporium (if indeed that is what you have) can be killed with isopropyl alcohol 90% or higher, which should also not effect Phenol (Bakelite). For lubrication you can use a product made by Caig called Fader Lube (I think its now called DeoxIT Fader F-Series) which will both keep the pot lubricated and inhibit the growth of resin eating fungus. This is the green DeoxIT product and not the red one. Buy the 100% solution in the squeeze tube or needle applicator; not the spray type which has petroleum based carriers which could be a problem with old style Phenols.
    N2EY likes this.
  4. N2RDQ

    N2RDQ Ham Member QRZ Page

    what I went for was to first use isopropyl alcohol for both de-grease and cleaning and to kill as much of the fungus as I could, using a soft brush to get as much of it off as possible. then followed that up with a mix of white vinegar with a little salt, this helped remove any tarnish from the metals, and also helped kill fungus as well. then gave it a quick rinse with water and dried it with compressed air.
    looks good so far, will post some pics later. I do have fader lube, but only the spray kind, I might use it but not spray it on, but spray it onto an applicator and put it on with that. I tell ya what it looks like they had in there was like axle grease. I was thinking maybe silicone grease might be more appropriate..
    N2EY likes this.
  5. N2RDQ

    N2RDQ Ham Member QRZ Page

    after some nosing around a bit more, and seeing some pics of disassembled clarostat wirewound pots ... I've gone with using archer Professional Gel Lube (same as super lube from what i understand) to lube the washer at the end of the shaft, the brass plate, and brush that connects to the center pin, and lastly lubricating the winding / brush area. pot works smooth as you would expect it to with no dropouts.

    the Lube itself is synthetic with PTFE, doesn't attract dust, and has a very wide temperature range -65 to 650F, it's quite thick and stays put and is non corrosive. seemed like the perfect lube for a 4w wire wound pot that will be placed in service with some tube equipment. I don't have to worry about it getting liquid when it gets hot, or gumming up over time, or gathering contaminants.
    I did consider the various deoxit choices, and nye reolube. seemed to me the deoxit lubes were too thin for this particular pot and they nye options seem to be good but didn't nessisarly offer me anything extra over the super lube / professional gel lube to justify 50 bucks and higher for a small tube.

    I believe this is pretty close to what the factory did but with modern lube. oh for anyone interested, I found a date code in the pot 13th week of 1936. nice to bring something that old back to life.. and it's going into a pice if vintage test gear mode with vacuum tubes, a Sprague TO-6A capacitor analyzer
    N2EY likes this.

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