How To Clean A Vintage Radio Tuner

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How to clean my tuning capacitor?

Word in 'Electronic Basics' started by Bill Bowden, Jun 1, 2013.

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1. It'due south an one-time (1960s AM radio) air dielectric, planetary drive with ball
   begetting 6X reduction). It'southward a very small mechanical cap measuring
   about ix/eight inch foursquare by 11/16 elevation with closely spaced plates
   (150pF and 100pF). Trouble is, the oscillator department jumps virtually 5KHz
   out of 1Mhz or perhaps 0.five% with pocket-size adjustments to the cap. Information technology
   appears it may be losing a ground connection (or loftier resistance) to
   the moving plates, or possibly some grit betwixt the plates. I assume
   the ground connection is fabricated through the ball bearings. I tried
   spraying some contact cleaner on the ends of the shaft but information technology didn't
   help. What would you suggest to restore the capacitor to it's original
   condition? I thought virtually soaking it in booze, but maybe that'south not
   a skillful idea.

   -Bill

3. "Bill Bowden" ** What did you use - Freon ?

   A few drops of WD40 on the bearings at each cease of the moving plates usually
   fixes it. Do not spray, use a syringe or the tip of a small screwdriver to
   utilize the liquid.

   Anecdote:

   A customer decided to fix his FM tuner ( Quad FM3) with the same problem.

   He sprayed WD40 all over the gang and nearby PCB - the oil layer left
   behind offset the local oscillator frequency by about thirty MHz, so correct off
   the FM band completely.

   After a lot of rinsing with turps and drying with hot air, I got it back.

   .... Phil

5. Nice pictures of ultrasonic cleaning results. Expect like new.

   -Bill

6. Yep, in that location is a bound blade contact at the opposite finish of the shaft
   as the ball bearings. Didn't see any silver, the blade appears copper
   or brass. I soaked the cap in alcohol for a day and moved the plates
   many times. And then I dried it the sunday and added a few drops of WD40 to
   both ends as Phil suggested. I removed the mica insulator and cleaned
   it separetely. Cap works much better now, but still a little eratic
   most the bottom of the ring where the plates are near fully airtight.
   Might demand some more WD40, or maybe some sparse sewing motorcar oil?

   -Bill

8. You created a coating that increased the dialectic constant for the
   plate that tune's the antenna..

   And then once more, could be the differences betwixt G and Due east line effects..

   Jamie

9. "Michael A. Terrell = Trolling Psycho"** The OP needed a contact cleaner FIRST.

   WD40 is that and and then it leaves a thin, oily film the lubricates and
   protects against moisture.

   ** Much the aforementioned as WD40.
   ** ROTFLMAO !!

   Using whatever sort of grease is never going to help a bad contact.

   Y'all FUCKWIT, RABID NUT Instance !!!!!!!!!!!

   
   ** Not unless there is a LOT of heat involved and no moving parts.
   ** Which makes it a good surface cleaner AND totally contradicts everything
   you lot just said.

   BTW:

   FOAD yous stinking TROLL !!!!!!!

10. "Bill Bowden"

    The cap got more erratic today, so I applied more WD40 and and then lost
    all signals except one 50KW station about 7 miles away. Everthing
    appeared normal, oscillator and antenna excursion both on correct
    frequency. It appeared the Q of the antenna excursion degraded
    drastically due to WD40 which may accept spilled on the capacitor
    plates.

    ** More likely rust or dirt particles from the bearings made it between the
    plates - carried by the Excess of WD40 yous practical.

    I have used WD40 successfully on intermittent tuning gangs in FM receivers
    many times, never any problem.

    BUT I used it sparingly and carefully !!!

    Yous may demand to utilise an evaporative cleaner on the plates now - ie stuff
    that smells prissy and disappears in seconds if you spray information technology on your paw.

    .... Phil

11. Yes, I think you are right. I disconnected the cap and connected an
    ohmmeter beyond the plates and read many points of low resistance. Then,
    I soaked the cap in a cup of isopropy rubbing alcohol and rotated the
    plates every few minutes and dried it out in the sun and and so applied
    a few drops of sewing machine oil and it seems ok now. I found
    someone who has a ultrasonic cleaner to loan and will attempt information technology out adjacent
    week.

    -Bill

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