Heathkit SB220 Problems

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

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  1. W1QJ

    W1QJ Ham Member QRZ Page

    They were probably the wrong ones. The stock suppressors work the best. I make clone originals with NOS carbon resistors. Obviousl;y if your suppressors were not original, whatever they are, are wrong. Show a digital of what you had there.
     
  2. K9NRA

    K9NRA XML Subscriber QRZ Page

    amp

    Here is what I have : $(KGrHqZ,!mIFGH(56LnUBRm638np2!~~60_57.JPG
     
  3. AF6LJ

    AF6LJ Ham Member QRZ Page

    If you can sometime today can you send a photo of the underside of the amplifier, I would like to see how you grounded the grids.
     
  4. K9NRA

    K9NRA XML Subscriber QRZ Page

    amp

    Not sure if I will get it torn back apart today, I used 14gauge wire all one piece on the grids and soldered, then took another wire and soldered it to that one and soldered it to the lug originally used to ground the caps and choke. All 14 gauge.
     
  5. AF6LJ

    AF6LJ Ham Member QRZ Page

    Not the right way to do it.
    You need three short direct wires to the chassis
    Connecting the grid pins together will not help. they care connected together inside the tube anyway.

    14 gauge wire is not good enough you need copper strap.

    This is the cause of your instability that led to your parasitic suppressors burning out. .
     
  6. K9NRA

    K9NRA XML Subscriber QRZ Page

    amp

    I can use strapping but dont have 3 seperate places to ground to. Someone earlier thought heavy wire would work. Can I use the strap and attach them to the original 2 grounds?
     
  7. AF6LJ

    AF6LJ Ham Member QRZ Page

    Not really.

    Short and direct and with wide conductors.
    9642661162_5abf3f535f.jpg
    Here is an example by WA7PRC in his SB-220.
    The grid leads are connected directly to chassis.

    Don't use wire use strap or in a pinch Coax Braid.
    Don't have the connection from the tub socket longer than an inch.
    Don't use tube mounting bolts to secure the strap to ground.
    Don't use the left over holes from caps and chokes that were stock.
     
  8. K9NRA

    K9NRA XML Subscriber QRZ Page

    amp

    That gives me a better idea on how to do it, thank you for the pic.
     
  9. K9NRA

    K9NRA XML Subscriber QRZ Page

    amp

    Will this stuff work? Is there thickness requirements on the strapping? I have some from .005 thick x.5" to .017 thick x.5" DSC09129.JPG
     
  10. AF6LJ

    AF6LJ Ham Member QRZ Page

    Glad to help....
    One final note...
    You do have a little latitude. like I said try to keep the leads short, about an inch from the socket lug to ground.

    To give you a little insight...
    Inside the tube that silver cone you see toward the bottom of the tube inside is the grid support ring, that ring is spit welded to the three grid pins. That forms a low inductance path to get the grid to the outside world.
    Connecting the tube socket lugs together at the socket can cause ground loops that can contribute to the amplifier being unstable. The picture I posted is from this thread...
    http://forums.qrz.com/showthread.php?372651-SB-220-Find

    I haven't directly grounded the grids yet in my SB-220 (Lovingly named Oscar) that will be part of phase two of Oscar's rehabilitation. There are a bunch of contributions to that thread along with plenty of pictures of my amp and what has been done to it to this point. It works great by the way, 1300W with a 100W drive.
     

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