Heathkit SB220 Problems

Discussion in 'Amateur Radio Amplifiers' started by K9NRA, Jun 11, 2015.

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  1. K9NRA

    K9NRA XML Subscriber QRZ Page


    I agree it's not the prettiest, but all I had to use was brass stock.
  2. W1BR

    W1BR Premium Subscriber QRZ Page

    I'd guess those resistors in the suppressors burnt up because of excessive inductance in the loops. What kind of output pwr were you able to make on 10 Meters?

  3. K9NRA

    K9NRA XML Subscriber QRZ Page

    I didnt check 10 meters, but 17 meters was about 1000W with 80-90 in.
  4. AF6LJ

    AF6LJ Ham Member QRZ Page

    The grounding looks better; that is acceptable.
    As for your parasitic suppressors. I can see why they smoked.
    As others have said too much inductance.
  5. WA7PRC

    WA7PRC Ham Member QRZ Page

    The original 3-1/2 turn inductors measured 80 nH on my AADE LC Meter.
  6. AF6LJ

    AF6LJ Ham Member QRZ Page

    I knew they were not much. 80nh sounds right.
    I would have guessed 50...

    One thing I would be concerned about...

    The carbon in those AB resistors has no effect on the inductance, 2W metal film resistors would have a slight effect on the inductance depending on the metals used in the manufacture of the resistor.
    Not enough to worry about at 28MHZ, but it would be interesting to measure with the resistor in place and one lead cut to see if the inductance changes....
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Those look a bit like the 'nichrome' parasitic suppressors which aren't very good.

    The originals made of tinned copper wire are better.

    My nichrome devices are in my toaster.
  8. AF6LJ

    AF6LJ Ham Member QRZ Page

    Simple and some say not too effective.

    The other extreme are the Ameritron suppressors found in amps like the AL-572...
  9. WA7PRC

    WA7PRC Ham Member QRZ Page

    80 nH was the inductor only. The A-B resistors measured 17 nH. That was after nulling the meter, and using short leads to/from the DUT.
    The point of the CC resistor is to swamp the inductor to decrease the Q. Its XL needs to be less than the XL of the inductor. Because of the inductance of the spiral winding, I wouldn't consider using a MF resistor.

    If you look closely, you'll see Silver Mica capacitors in series with each resistor. The only explanation I can give is to counter series XL in the resistor.
    Last edited: Jun 21, 2015
  10. W1BR

    W1BR Premium Subscriber QRZ Page

    W8JI mentioned the reason they were used--I suspect you are correct about compensating for the reactive value of the resistors.

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