Heathkit sb-200 repair tech

Discussion in 'Amateur Radio Amplifiers' started by KB9LQA, Apr 15, 2012.

Thread Status:
Not open for further replies.
ad: L-HROutlet
ad: l-assoc
ad: l-innov
ad: l-Waters
ad: l-gcopper
ad: L-rfparts
ad: l-rl
  1. KB9LQA

    KB9LQA Ham Member QRZ Page

    Can someone tell me if they are aware of a good tech to repair a Heathkit sb-200, in the Milwaukee Wisconsin area.
    I think it may be time to get some help with it. Thanks, Chris.....
  2. W9GB

    W9GB Ham Member QRZ Page

    Chris -

    You can always contact Miles Cundy at AES-Milwaukee (Head of AES Service department for 40 years!)
    for references of local (reliable) technicians or Elmer to help you with project.

    Since this was originally a KIT, the Assembly Manual
    has virtually all information you need for Build // Rebuild.

    Harbach Electronics carries many common restoration parts.
  3. KO6WB

    KO6WB Premium Subscriber QRZ Page

    Could you tell us what the problem is? There are a lot of folks that have or had a SB-200 and they may have some valuable advise on how you can do the repairs.
  4. KB9LQA

    KB9LQA Ham Member QRZ Page

    Hello, and thanks for the response. I have hooked it up to a dummy load to test(also tryed with an antenna) It has 2300 volts of hv. When I key the amp the idle current is 60ma. When i switch the meter to grid, the meter pins full scale. That is without any power from an exciter. It was suggested to me that it sounded like a bad tube. I have tryed 3 sets of tubes, one of them I have just perchased new. No change. It does have continuity in the B+ line from the power supply board to the top of the tubes. I did replace the 33 ohm resistors on the tube sockets that were out of spec. also the caps in that area that appeared to have run hot..... I purchased it from an estate, so i dont know all the history. It did come with the manuals, and has the Harbach power board , soft start, soft key, fan, and relay, upgrades. I would like to repair it myself, just not sure if I can. Any advice would be appreciated, Thanks, CHRIS.....
  5. W1QJ

    W1QJ Ham Member QRZ Page

    60 mills idle is low, 2 tubes should idle at 90ma. The grid meter pinning, there should be no grid current at all with no drive, Since a Harbach relay was installed, should make sure it was done correctly because it is NOT a drop in relay, there must be a resistor as well. Check to see it was done properly. Grid current is read across a 1.5 ohm resistor that should be checked Check the meter switch and make sure the lower tab is not grounding to the cabinet.
  6. KC8VWM

    KC8VWM Premium Subscriber QRZ Page

    Agreed, Sounds like a meter switch problem.
  7. W4AFB

    W4AFB Guest

    Those meter switches are notorious for getting dirty and having bad contacts. Make sure you check that. Does the amp tune up and produce power?
  8. KB9LQA

    KB9LQA Ham Member QRZ Page

    Thank you, for the replys, I did double check the relay, and its marked potter- brumfield, dont think thats a harbach unit, my mistake. It does have the original 2000 ohm resistor attached, but it only reads 1055ohms, when in place. When tested with an exciter, 50 watts in ,and only 10 watts out, it does tune a little, didnt try to long , to prevent any more damage. I still need to take a better look at the meter switch, thanks, CHRIS.....
  9. W9GB

    W9GB Ham Member QRZ Page

    Did this amplifier ever work correctly, since you have owned it??

    Do you have a 50 ohm dummy load??
  10. KB9LQA

    KB9LQA Ham Member QRZ Page

    W1QJ and others, It turned to be the 1.5 ohm resistor. It was open. and burnt.I replaced it with a 1.5 ohm half watt resistor. (half watt is ok???) Now 90ma idle current, grid meter doesnt pin or move, till i excite it. 50 watts in 550watts out on 10 meters, in to a dummy load. I will still check the amp over ,clean switches ect. I still need to upgrade my license to put the amp on the air, I am working on that also!! THANKS, to all that took the time to respond.CHRIS.....
  11. W9GB

    W9GB Ham Member QRZ Page

    Sounds like R15, which leads from 572B grids and to Antenna Relay.

  12. K1ZJH

    K1ZJH Ham Member QRZ Page

    R15? If it was my amp I'd want a metal oxide in there, and at a higher wattage than what Heath used.
    Adding Back to back protection diodes across the multimeter coil might be a good idea.

    If a tube flashes and blows the resistor while you're measuring grid current, I suspect it could take
    out the meter too. Maybe someone else can comment, since i am more familiar with the SB-220 meter
    circuit and I could whistling Dixie, and the schematic I'm using is a very poor copy.

    But at a quick glance that looks like the grid current metering resistor. Nothing good takes out that resistor.

  13. W1QJ

    W1QJ Ham Member QRZ Page

    Ok, well I thought that the 1.5 ohm might be the problem that's why I asked you to check it. You may want to up the wattage on it and use a good 1% or 2% rated one. They are pretty cheap these days. You should be OK for a while if you don't hold key down too long. Glad you didn't have to ship it out. Now you have 90MA idle and that is right on the money.
  14. KB9LQA

    KB9LQA Ham Member QRZ Page

    Thanks again for the help, I will upgrade the resistor!!
  15. AG6K

    AG6K Ham Member QRZ Page

     Indeed Pete. . . There are two possibilities when a grid resistor blows. To find out which one it was remove the tubes and measure the anode to grid leakage current at 2x the rated anode potential with a breakdown voltage tester (BVT). If the measured current is less than 10uA, the tube did not flash over. Instead, the burst in grid-I that blew the resistor was caused by an unloaded condition - for which there are also two possibilities. 1. the antenna became disconnected or 2. there was an intermittent burst of VHF energy that was blocked by the HF-tank -- which acts as a LPF. To discourage VHF parasitic oscillation, reduce the Q of the VHF suppressors It's also a good idea to incorporate extensive glitch protection in any amplifier.
Thread Status:
Not open for further replies.

Share This Page

ad: dxeng