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. W1QJ

    W1QJ Ham Member QRZ Page

    Then get the direct replacement from RF Parts, this way you don't have to worry about changing the resistor, just change the relay.
     
    K4AGO and WA7PRC like this.
  2. KD0SGX

    KD0SGX Ham Member QRZ Page

    Ok what is the part number needed from RF parts that I need?
     
  3. W1QJ

    W1QJ Ham Member QRZ Page

    It appears that RF parts has the original relay. Check the part number on the old relay and compare to the ones sold by RF parts. Pick the same number. If you don’t have the original relay I can get you the part number.
     
  4. KD0SGX

    KD0SGX Ham Member QRZ Page

    Yeah I know the part number 68-5, not just any old relay will work as we have bias in play here so it needs to the right one with the right resistor which I'm sure you know.
     
  5. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Given the difficulty in sourcing the original part I'd just buy a DPDT 110V relay that fits mechanically, measure the keyed idle mode current and adjust the resistor value as necessary if the current is too high or too low.

    Either that or I'd hard ground the grids, change the metering and bias circuitry and then the coil resistance really doesn't matter. That's what I did with my SB-200 but it is a bit more of an undertaking than just making a measurement and adjusting the resistor value accordingly.
     
    WA7PRC likes this.
  6. W1QJ

    W1QJ Ham Member QRZ Page

    Changing the SB200 to grounded grids isn’t for the beginner. It’s an advanced modification that requires a full understanding of biasing grounded grid amps and how metering plate and grid current is accomplished. I’d venture to say that most likely all the 110vdc relays made by P&B have the same coil. I looked at the relays listed for 120vdc and except for the relay current specs they are probably the same otherwise. I’d select the DPDT 10 amp unit and just install it as a swap. If you idle current is close to 90ma you are good.
     
    KD2ACO likes this.
  7. K7TRF

    K7TRF Premium Subscriber QRZ Page

    Agreed.
     
    KD2ACO likes this.
  8. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    If the idle current is out by more than about 10ma, we'll help you get it dialed in. It's actually easy to adjust if the relay coil resistance is significantly different than what was in there.
     
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  9. KD0SGX

    KD0SGX Ham Member QRZ Page

    Well if anyone can source a relay and resistor as a valid replacement without have to bias grids or make current measurements
    I would greatly appreciate it. I have replaced and rebuilt the power supply and soft key , numerous caps ect..working great now, but want a replacement on hand. Someone must have a pre-built working idea?
     
  10. KD0SGX

    KD0SGX Ham Member QRZ Page

    Would rather someone else who has upgraded with newer part just give advice on Relay source and resistor used. Seems like eventually someone with replace one or has already with out measuring currents.
     

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