Elecraft K3S and Heathkit SB-200 hookup advice

Discussion in 'Amateur Radio Amplifiers' started by N8MDC, May 8, 2021.

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  1. N8MDC

    N8MDC Ham Member QRZ Page


    The WVU Amateur Radio club has been wanting to get our hands on a nice amplifier for a while, and we finally got a good deal on a recently restored Heathkit SB-200 in great condition! The seller also threw in an Ameritron ARB-704 to help in interfacing with more modern rigs. Once we ran through its initial test procedure to make sure everything is working as expected, we sat down and started figuring out how it could interface with our primary HF rig, an Elecraft K3S.

    Logically, the most appropriate way to hook it up would be:
    Elecraft key out -> 704’s Radio port
    SB-200 Ant. relay -> 704’s Amp port
    SB-200 ALC -> 704’s ALC

    I can’t really think of any other way that this could be hooked up, but I wanted to hear verification from someone more experienced with the SB-200 and 704 before I try to key up and potentially damage the K3S. I’ve already verified that the K3S keys the 704 properly, but I haven’t tested yet with the SB-200 fired up. Any insight would be much appreciated!

  2. K7GQ

    K7GQ Subscriber QRZ Page

    Ditch the ALC connection - it will serve no useful purpose with any K3(S).
    K0UO likes this.
  3. W1QJ

    W1QJ Ham Member QRZ Page

    The ALC probably isn't compatible so don't use it, just limit the drive level from the K3 with its power level control. Also you should go into the K3 menu and set an RF delay for 20-30ms whichever is longest in the menu option.
    K2XT likes this.
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Indagudoldaze (you were probably there), everybody using SB-200s were using tube rigs most of which could generate more output power than a K3 could and had no way to turn the output down on SSB. And we rarely used the ALC connection.

    I'd also forget about it with a K3.

    The OP says it's a "restored" SB-200, in which case I'm amazed someone didn't already modify it for low-voltage keying, which is probably the #1 mod that everyone makes. But maybe they just never did that.

    Way before Harbach et al., I'd always just add a 12Vdc cube relay inside, coil driven by a voltage doubler fed by the filament transformer and use that to key the "real" original circuit. Cost $5, takes 30 minutes, and works fine (although adds another relay delay in the keying system, so add another 15-20 mS). I thought everybody did that, going back to the sixties.:p
  5. N8MDC

    N8MDC Ham Member QRZ Page

    Yes, you are correct in that the internals are unmodified from the original construction. The tubes and capacitors were replaced circa 2013 based on what the previous owner told me. I'm happy to report that I followed the advice to ditch the ALC connector, and everything appears to be functioning properly! Got some nice signal reports using the amp, and power readings suggest that she's working great. I've seen some of those modifications myself-- after I've had some fun playing with our extra couple (hundred) watts, we plan on looking into said mods.

    Thank you all for the advice and insight!
  6. K2XT

    K2XT Premium Subscriber QRZ Page

    What ever happened to the SB200 that used to be there, built in 1967 and run at W8CUL driven by an SB100 into a quad antenna on the roof with a beautiful view of the Creative Arts center from the 13th floor in the penthouse?

    (Now how in the heck does he know that?)
  7. K2XT

    K2XT Premium Subscriber QRZ Page

    Hey Louie, This guy is from the world famous W8CUL. We will get him whatever he needs.
    "From high atop the Engineering Sciences Building on the Evansdale campus of West Virginia University, THIS IS W8CUL, The West Virginia University Amateur Radio Club station, calling CQ DX and standing bye."

    The best 4 years of my life, 1964-68.
  8. K2XT

    K2XT Premium Subscriber QRZ Page

    The K3 can key +200 vdc at 5 amps. (page 17 of the manual). No interface needed.
    The delay menu item is called TX DLY and the max setting is 20 ms. It should be set there to not hot switch the amp, no 704 interface needed.
  9. W1QJ

    W1QJ Ham Member QRZ Page

    The sb200 has a negative voltage .
    K2XT likes this.
  10. K2XT

    K2XT Premium Subscriber QRZ Page

    Why would relay contacts care? I wonder if Elecraft just meant 200 vdc vs 200 vac?
    I should look at the schematic and see if there is a diode in the path of the contacts. Will do.

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