Heathkit SB-230 Amp

Discussion in 'Amateur Radio Amplifiers' started by WA6MHZ, May 26, 2012.

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  1. WA7PRC

    WA7PRC Ham Member QRZ Page

    You could start with the 8873 datasheet. It shows worst-case IP = 500mA The only documentation I have for the SB-230 is the schematic, which doesn't say what type of fuse. What was in the amplifier? If it was ¾A, ask yourself why it was blown.
     
  2. AG6K

    AG6K Guest

     The Funderberg gold-sputter test might be in order.
    http://www.somis.org/Goldmeltballs.html
    Do not assume that a tube with loose gold meltballs inside is useless. Phone me if you detect gold leakage and I will explain how to move the meltballs out of harm's way.
     
  3. KM1H

    KM1H Ham Member QRZ Page

    The first thing I would do is limit the drive to 50-60W and a good tube should result in 500W+ out. A blown grid fuse means that the grid was already well overdriven before the fuse blew so Id be real careful in the future.

    Ive been using a SB-230 I converted to 6M about 25 years ago (A low cost Dayton score with a bad tube and a good used one a few aisles away for cheap) for portable work and would be interested in that NOS tube from New Zealand.

    Carl
     
  4. AG6K

    AG6K Guest

     With A0 the rating is 350mA max. With SSB or pulse tuneup 500mA is max. To see cathode damage from overdrive see photo on p.17 in "Parasitics Revisited" Part-1 in the September, 1989 QST Magazine,. If a 0.75A grid fuse blows in an 8873, odds are that it was from an intermittent UHF parasitic osc., not from overdrive.
    If you do not have this issue of QST, e-mail me at r@somis.org and I will send a JPG of p.17 to you. - note - the file is 9MB.
     
  5. WA7PRC

    WA7PRC Ham Member QRZ Page

    I don't have it but, since I have zero interest in using that tube, no thank you. Also, if a JPG is 9MB, the resolution is WAY too large. Emailing such a large file is silly. Back to the plonk file.
     
  6. WA6MHZ

    WA6MHZ Premium Subscriber QRZ Page

    I just got the 9-38PF Cap for the plate tuning of the 6 meter circuit. I also have the full writeup done by fellow 6 Meter enthusiast Terry N6CW here in town on his mod for the 6M conversion. Think I will recap and rediode the PS first, and install protection circuitry. Also have to score some 8 gauge wire for the final coil. I SURE don't want to build this thing only to have the 8873 blow out! Already saw 500W out of it. I don't like the meter in the thing. The SB-200 had a large robust meter while the 230 has a little RINKYDINK meter. Maybe I will redo the front panel to incorporate new metering. This doesn't have to be a Museum piece if it is going to be in operation. Too late for the June VHF contest, but it should be ready to go for 2013!
     
  7. WA7PRC

    WA7PRC Ham Member QRZ Page

    I guess you're going to convert it, after all. Soft copper tubing can be found in 1/8" diameter. #8 is 0.1285" OD. The tubing would be easier to bend and lighter.
     
  8. WA6MHZ

    WA6MHZ Premium Subscriber QRZ Page

    It really is a tough decision. Keep it cherry for a Museum piece (For 100% complete SB-104 line), or convert it to 6. I need a 6M PA badly and was going to convert the SB-200, but universally it is said the 230 is a far better choice because the tube is good for VHF/UHF which the 572s are marginal at. So maybe I will just pull the front panel, put it in a case as a Mockup of a SB-230, and build my own front panel with the new meters. I don't need a bandswitch or most of the final tuning parts (I will use the Plate cap for a load cap on the conversion). Someday I may come across another SB-230 I can grab to use for the Museum. maybe one with a blown tube or one butchered up.

    The Antenna relay needs to be replaced with a Dow Key for better RF Switching at 50 Mhz. I have a Plate HV and I meter. Need one for Grid and RF output.
    so this won't look like a SB-230 after I am done, but it will be a spectacular 6M Kilowatt!
     
  9. AG6K

    AG6K Guest

     the whole page is pretty detailed so I had to scann it at 500dpi to stop the herringbone effect. Here's a cropped version of only the 8873 with the damaged cathode:

    qst.sept.89.p.17crop.jpg
     
  10. AG6K

    AG6K Guest

     Eimac lists the drive to 8873 as 26w. Exceeding 350mA of anode-I key-down may cause cathode flaking.
     
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