SB-200 Looking for the T/R relay? Harbach sold out.

Discussion in 'Amateur Radio Amplifiers' started by KD0SGX, May 10, 2020.

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  1. K7TRF

    K7TRF Premium Subscriber QRZ Page

    That's a 12V relay. The SB-200 uses a 120V relay.
  2. KD0SGX

    KD0SGX Ham Member QRZ Page

    Or someone could possibly give a relay suggestion with the proper resistor to use who may already have figured it out or who has the smarts to test and not die.
  3. W1QJ

    W1QJ Ham Member QRZ Page

    I’ll repeat, I will get the last relay Harbach was selling and a resistor and mail to you.
    W1TRY likes this.
  4. K7TRF

    K7TRF Premium Subscriber QRZ Page

    There is no safety hazard when testing for the proper resistor value. You just key the amp with no signal and look at the front panel meter on the amplifier itself. There's no need to get in the operating amp with any kind of test instruments. If the current is too high or too low you won't damage anything it just means the amp's designed linearity and efficiency will be off a bit until you compensate by adjusting the value of R18.

    If for instance the idle current is a bit high (say 120 mA) the amp will actually be more linear and should put out a bit cleaner SSB signal but the efficiency will drop as the amp has moved closer to Class A operation. You could run the amp this way but you'd want to back off your max power a bit to ensure long tube life as plate dissipation would increase at the lower efficiency.

    If the idle current is a bit low (say 50 mA) the amp will be a bit less linear which could increase SSB splatter but the amp will also be running a bit more efficiently and dissipating less idle mode power which would be ok for CW use but not ideal for SSB use.

    That's all the combo of R18 and the coil's resistance does, it just shifts the idle mode current and operating class of the amp a bit but doesn't really create a dangerous situation.

    I'd take Lou up on his offer and just have him send you a relay and resistor...
    KD0SGX likes this.
  5. KD0SGX

    KD0SGX Ham Member QRZ Page

    I sent you a PM, send my how much and I can Paypal or Venmo you. This is new?
  6. W1QJ

    W1QJ Ham Member QRZ Page

  7. K4ADS

    K4ADS Ham Member QRZ Page

    k5svc on eBay sells Potter and Brumfield T/R relays for Heathkit SB-200 just like original. Search for Heathkit SB-200 to find it. I just received one and the pull-in coil is open. I've emailed them and haven't heard back yet. Hopefully they will honor the defect.
  8. W1QJ

    W1QJ Ham Member QRZ Page

    The K5SVC relay indeed has the right impedance but it’s rated at AC voltage. It does work so if he has more I wouldn’t hesitate to use it. I’ve installed one already and it seems fine.

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