SB-220 C4 Overheating

Discussion in 'Amateur Radio Amplifiers' started by NE6I, Oct 18, 2014.

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  1. AF6LJ

    AF6LJ Ham Member QRZ Page

    Good post Carl, thought provoking.
  2. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    Thanks, but I never had an Avatar.



    AC0OB - A Place where Thermionic Emitters Rule!
  3. KA9JLM

    KA9JLM Ham Member QRZ Page

    It shows as a broken page. I just wanted to make sure you see what we see.

    I guess QRZ does not have a Default, and it just errors out.

  4. NE6I

    NE6I Ham Member QRZ Page

    Definitely enjoying the conversation about the potential mods to the SB-220. Again, thanks everyone for helping me locate the defective part. I have replacement chokes on the way and hope to have the amp back up in a few days. I do need to have it up for the FT4TA DXpedition coming up on the 30th. After that, I'll consider various mods to improve the SB-220.

    Re: the one poster that wondered what band was last used before the problem arose...I think it was 10m.
  5. KA9JLM

    KA9JLM Ham Member QRZ Page

    I figured it may have been on one of the higher frequencies.

    Good Luck on your project.
  6. WA7PRC

    WA7PRC Ham Member QRZ Page

    Since they are the source of RF ground for the tube grids, you'll want to verify the six 200pF mica capacitors are still good. If any are not OK, they all should be replaced.
  7. KM1H

    KM1H Ham Member QRZ Page

    Especially if they are the early rectangular ones as Ive already mentioned. The dipped silver mica seem to hold up far.
    I even leave the RFC and caps in for 6M, absolutely no instability unlike the some of the competitions.
  8. NE6I

    NE6I Ham Member QRZ Page

    None of the caps are shorted but I don't have a capacitance meter to check them further unfortunately.
  9. WA7PRC

    WA7PRC Ham Member QRZ Page

    Most handheld multimeters that can measure capacitance aren't very accurate below about 1000pF but, the Almost All Digital Electronics LC Meter II is excellent for measuring small values of L & C (1 nH to 100 mH and 0.01 pF to 1 uF).
  10. KA9JLM

    KA9JLM Ham Member QRZ Page

    The key is to keep the test leads as short as possible, Or connect the cap directly to the meter.

    And turn off the Fluorescent bench light.

    Have Fun.
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