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Amp Arcing

Discussion in 'General Technical Questions and Answers' started by N9CM, Dec 7, 2017.

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  1. N9CM

    N9CM Ham Member QRZ Page

    What is the general remedy for a plate cap (variable) arcing sometimes during tune up for 160? A corona cap on the 160 switch position? Something with the load cap cap?
    Last edited: Dec 7, 2017
  2. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    1. Cleanup of all carbon and metal residue with careful detail.
    2. Sanding, smoothing of any pitted or jagged metal surfaces to reduce arc potential.
    3. Painting over tracks in PCB material with Glyptal varnish, electrical varnish or corona dope to cover conductive/contaminated arc tracks.
    4. Possible repositioning of capacitor and other components to increase distance.
    5. Cover arc points with insulation. Flat surfaces may be improved by covering with Kapton tape or Teflon sheet (available from McMaster or Grainger).
    6. Ensure antenna is adjusted for best SWR to minimize load on tuner.
    7. Keep a log of freq. vs. tuner settings for reference.
    8. Tune at minimum power.


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    p.s. Glyptal and Corona Dope have dozens of uses in the shack.
    Last edited: Dec 7, 2017
  3. N9CM

    N9CM Ham Member QRZ Page

    This is a very fine spaced variable cap. Don't think you can file or sand between the fins without adding potential damage. On some older amps this was done, not sure why on this amp...antenna swr is well below 1.5 to 1 or better...
  4. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    Then you can expect to have repeated and worsening arcing problems under the same conditions if no repairs or precautions are taken. Replace all damaged parts, otherwise. Consider repackaging into a larger enclosure.

    1.5: 1 AT THE ANTENNA? I suspect not. Otherwise there is no reason to use a tuner.
  5. N9CM

    N9CM Ham Member QRZ Page

    I do not use a tuner. This is the tuning cap inside the amp. Obviously, if no corrective action (which I am asking about ) is implemented you will have to run it at a lower output power level. Doubt I can locate (have looked) for replacement tuning caps for the amp also.
    KB4QAA likes this.
  6. WA6MHZ

    WA6MHZ Subscriber QRZ Page

    I had a SB-220 that arced terribly on the Tune cap until I installed the QSK mod which replaced the old frame relay with Vacuum relays. the problem went away. W7RY thinks most of the arcing is caused by slow relay transfers. and my experience agrees with that.
    K2XT and N5DMC like this.
  7. W2VW

    W2VW Ham Member QRZ Page

    Maybe something is out of place and it is reducing spacing.

    Can you tell exactly where the cap is arcing?

    The plate tuning cap should not be all that close spaced to begin with.

    Details and pictures help. What amp is it?

    Does it fault when tested into a dummy load?
  8. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Are you sure you're referring to the TUNE capacitor and not the LOAD capacitor?

    The TUNE capacitor in a TL-922 (if that's the amp you're discussing) is not very close spaced.
    KC8VWM likes this.
  9. KC8VWM

    KC8VWM Moderator Volunteer Moderator QRZ Page

    That's an excellent point. Need to isolate the problem further by taking the antenna out of the equation.
  10. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    I would take a long look for other damage or causative components. Perhaps the anti-resonant coil, resistors & caps. Good grounding throughout due to age....

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