SB 220 arcing tune capacitor

Discussion in 'Amateur Radio Amplifiers' started by N9CQB, Jul 26, 2020.

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  1. N9CQB

    N9CQB Ham Member QRZ Page

    I bought an old SB 220 recently. It has a new capacitor bank and relay. Everything else looks like stock.
    After several weeks of use on CW, SSB and FT8 the tuning capacitor is starting to arc after it's been correctly tuned for the freq
    The cap had a lot of dust so I cleaned it and filed down the spots that were damaged. There were a couple of spots, but the majority of the plates were clean. The plates cannot be removed- they are pressed onto the rod.
    After re-installing, the cap still wants to arc
    Should I buy a new one or is there a modification to prevent the arcing?
     
  2. WN1MB

    WN1MB XML Subscriber QRZ Page

    Prepare for heavy incoming.
     
  3. KL7SG

    KL7SG XML Subscriber QRZ Page

    Hi, I have an SB220 and had to replace the T/R to get rid of arcing. The amp T/R relay had a burnt contact. It was pretty easy to see. Also, the capacitor plate spacing was wrong. The movable plates need to be in the center of the gap. If the relay and cap look good, check your cabling to the antenna.
     
  4. AG5CK

    AG5CK Ham Member QRZ Page

    I would check the parasitic suppressors also. It's heartbreaking when a shiny new cap arcs.
     
  5. N9CQB

    N9CQB Ham Member QRZ Page

    The
    T/R relay is new-just replaced b4 I got it. The rotor plates are in the middle of stator plates also
     
  6. N9CQB

    N9CQB Ham Member QRZ Page

    Check them for what? Signs of arcing also?
     
  7. AG5CK

    AG5CK Ham Member QRZ Page

    See if the resistors have been cooked and are out of tolerance.
     
  8. KL7SG

    KL7SG XML Subscriber QRZ Page

    Does this happen on all bands? Also, do you run out of adjustment on the tune or load capacitor(s)
     
    Last edited: Jul 26, 2020
  9. W1QJ

    W1QJ Ham Member QRZ Page

    It’s probably time for new parasitic suppressors as age floats the resistors up and if they ever overheated they are gone. You should time the relay. Get yourself a wide spaced tune cap. I can help you with everything.
     
  10. N9CQB

    N9CQB Ham Member QRZ Page

    Happens intermittently on all bands in SSB mode. arcing is on front plates of tuning cap
    Resistors look old but not burnt on parisitic suppressors
     

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