The SB-200 on 6: A MONUMENTAL Project!

Discussion in 'Amateur Radio Amplifiers' started by WA6MHZ, Oct 2, 2012.

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  1. WA6MHZ

    WA6MHZ Subscriber QRZ Page

    I AM a good tech! Maybe not as good as you, but I SURE have fixes hundreds of really broke radios, plus lots of Microwave radios here at work. That is also why this facility is informally known as the RADIO HOSPITAL!
     
  2. N2EY

    N2EY Premium Subscriber QRZ Page

    So....the thing to do is to hunt up all the missing RF parts and get it working again as an HF amp, then tear those RF parts out again and convert to 6? That makes no sense!

    No, you are.

    What was bought wasn't an amplifier. It was a chassis with some parts on it, that could be used to make a 6 meter amp.

    IMHO, the thing to do was to completely dissassemble the thing, then clean and test every part. Work up a new design, complete with schematics and sketches of layout. Calculate new 6 meter pi-networks and metering system. Then build a new 6 meter amp with the usable parts. Add what is needed. But keep it simple!

    Of course that's a lot of work. But it's the right way to do it.

    73 de Jim, N2EY
     
  3. N2EY

    N2EY Premium Subscriber QRZ Page

    Maybe.

    But this isn't a fix-it job. It's a conversion/restoration/custom job, and requires some design work that repair jobs don't. We don't even know if the original amp ever worked right!

    The nature of the problems demands that a logical, step-by-step approach be taken, rather than simply tossing new parts in, hoping to find the right fix.

    Being able to repair something is very different from being able to build something new. This is closer to new construction in many ways.

    I really want this project to succeed - but it seems my advice isn't making much difference. (sigh).

    73 de Jim, N2EY
     
  4. W1QJ

    W1QJ Ham Member QRZ Page

    I bought SB-200 amps all the time to convert to 6 meters. #1 priority was proper working power supply with proper idle current etc with good tubes and a working meter. This is not a major requirement. I don't care if it was wrecked to 11 meters or has a blown band switch. Just a half way decent bare bones working power supply unit. Once obtained I can go right to work on the conversion, no messing around with fabricating a meter, and changing relays, and trying to figure out how to rebias the thing with non stock relays etc. I go right to work on the conversion and 6 hours later its a working 6 meter amp ready to go on the air and make contacts. If I wanted a test in my rebuilding skills and a challange I would try to fix some other type of radio equipment that would be worth alot more when fixed. Spending this kind of time and effort on an SB-200 is crazy when one can buy one in nice working condition for a tiny bit more than a parts amp. Mind you, I am NOT against a challange of skills or a learning project, I would simply opt for a different type of radio to repair so I can get more money for when fixed. You'll have enough problem getting it to play good on 6 meters without all the hassle of just getting the thing to be DC worthy.
     
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I'd like to start an SB-200 conversion project, myself.

    I don't have a complete SB-200 but I do have sheet aluminum and some green spray paint.

    Almost there!
     
  6. N2EY

    N2EY Premium Subscriber QRZ Page

    Reminds me of the woodworker who wanted an oak cabinet and started by planting an acorn.

    73 de Jim, N2EY
     
  7. WA6MHZ

    WA6MHZ Subscriber QRZ Page

    A very gracious and generous benefactor out there in QRZedland sent me a sheet of aluminum cut out for the size of the SB-200 front panel. Also a perforated aluminum top to keep me safer.

    Here is the new front panel after I drilled the holes and rounded the corners.

    [​IMG]

    and the new top

    [​IMG]

    So the plan is to cut TWO holes for 2 separate new meters. One will be in the Final Compartment so that will require extensive shielding. But there is now room since the bandswitch is gone.
    I will have one for the HV, and one for the Plate Current. This way, I can do away with the SB-200 meter circuit and build a whole new one. THEN I can see what is really happening. It could be the lousy corroded meter switch is messing with me. Plus, the sticking meter needle is messing with me big time too.

    [​IMG]

    The Meter switch can be replaced with another that will only measure Grid current, HV and RF out. No real need for SWR, as that is done with external metering. Also, this way the existing relay can be yanked out as well as the SWR bridge (will have to make up a Power Output sense circuit). Maybe I can stick a DOW KEY relay in there. Or Two.

    Eliminating all these areas of error will give me a better chance to make this work. I probably still will need to get some more 572Bs. Watching at the Swapmeets for those. Saw some listed on here, but they were priced above what you can buy a new pair at RF Parts for!!!
     
  8. WA6MHZ

    WA6MHZ Subscriber QRZ Page

    See! It is getting MORE homebrew every day! Not a conversion anymore!
     
  9. W5WPL

    W5WPL Ham Member QRZ Page

    That's a darn nice fella who sent you those panels.
    I think they rest of the Zeders should send him a Hallicratfers SR-400 Cyclone III with the PS-500A power supply.
    It's the lest we SHOULD do.

    Hay Pat, I was happy to do it for you.
    I'll offer the same to anyone else here.
    If it is not too difficult I will be happy to help anyone here with
    they're sheetmetal project. Just pay for my shipping charges.
    I will not punch holes because of the problem making sure of that the right size and location is correct.
    The holes have to be American Standard. 30 years of shop work should help.
     
    Last edited: Nov 26, 2012
  10. AF6LJ

    AF6LJ Ham Member QRZ Page

    Good Deal Pat, and Bill............
    Good to see this project is moving along.
    Can't wait to see the next steps....


    Cool!!!!!
     
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