The SB-200 on 6: A MONUMENTAL Project!

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

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  1. WA4OTD

    WA4OTD Ham Member QRZ Page

    You go Pat! Always a lot to learn from you when you repair/build or experiment.

  2. AF6LJ

    AF6LJ Ham Member QRZ Page

    That takes all the fun out of it.
    An hour to repair / convert an incomplete SB-200 to Six Meters?

    Yah I really don't think so.
  3. WA6MHZ

    WA6MHZ Premium Subscriber QRZ Page

    It isn't a repair type situation. When I got the chassis, it was basically a transformer and a few chassis parts to which I added the missing and needed stuff to make it work. So no one can "repair" something like this. And besides, that isn't the point.

    In the beginning, I was going to build the amp from the ground up. All I wanted was a SB-200 Power transformer but I got this derelict, decrepit chassis with it. I SHOULD have just yanked the transformer and started from scratch as I had planned. But I got LAZY and used some of the existing circuitry still there. It save alotta metalwork and money. And I WAY WAY Overpaid for the chassis. Something like $200 fighting off RBs on Ebay for it. I bet the seller was TICKLED! He had no idea he would get that kind of money from it. he would have been happy to get $20-$50 for it! But, because of the RBs and I REFUSING to be outbid this time, I paid that much for it.

    I have to go to the QCWA meeting now, but when I get back, I will work on it some more. The difficulty I am having measuring the Plate current is because of the P.O.S. meter I have in there. Once again, I didn't want to tear apart a good working HM-102 (which I paid $20 for at the Swapmeet) so I used another HM-102 meter that turned out to have a sticky meter movement in it. It is almost useless. Have to tap on the meter face to get the needle to move. So I am in the market for JUST a HM-102/HM-2102 meter movement to replace with this one.

    Maybe I can put a voltmeter across the meter leads and watch the meter that way. I do suspect there is something fishy about the metering path, but I can't find it DC wise. Everything is correct. So will work some more on it this afternoon. But it is a hair tearer!
  4. AF6LJ

    AF6LJ Ham Member QRZ Page

    Can't wait to read it when I get back this evening.
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I think it's the phase of the moon. October 30 was a full moon, it should have worked.

    Now it's only about 60% moon, might have to wait 'til it's full again.
  6. N2EY

    N2EY Premium Subscriber QRZ Page

    Anything can be repaired if enough new parts are added. I've got a 50 year old hammer that's been repaired several times - two new heads and six new handles.....

    But as you say, that isn't the point.

    Ebay fever....

    There's a much easier way.....

    Don't hack apart good equipment just for the meter. That's a waste.

    Instead, look through your inventory and come up with a couple of nice meters that don't go with anything. They don't have to be Heathkit meters, either.

    Figure out how to wire in Meter #1 to measure the plate current, Meter #2 to measure the grid current, and Meter #3 to work with the SWR bridge.

    This lets you monitor what's actually going on without tapping meter faces and such nonsense. If the metering circuits are properly designed, there will not be HV on the meters.

    Then find a piece of sheet aluminum that's the appropriate size of the SB-200 front panel and make a new front panel with holes for the meters, controls where you want them, switches, indicators, etc. Paint job and labeling can be whatever you want. The old panel can be used as a template for holes that are the same in both panels, making layout easier. IIRC the front panel of the SB-200 is just a flat plate. The old panel can be saved as a spare or sold off on eBay.

    The designers of most ham gear used only one meter and a switch because it was cheaper that way. You don't have to.

    73 de Jim, N2EY
  7. N2EY

    N2EY Premium Subscriber QRZ Page

    I guess you didn't look at the pictures nor read the copy that went with them. What he got was an SB-200 with most of the tuned circuit stuff gone but most of the rest intact. Which is fine if the goal is a dedicated 6 meter amp.

    The problem is that the condition of the parts and wiring before conversion is/was unknown.

    Read the whole thread. It's a bit fascinating, really.

    73 de Jim, N2EY
  8. AF6LJ

    AF6LJ Ham Member QRZ Page

    That's not it;
    I understand Mercury is in retrograde.
  9. N2EY

    N2EY Premium Subscriber QRZ Page


    I am NOT going to be part of any Zed group-dance-and-sing of "Aquarius"!!!

    Not again, anyway.

    73 de Jim, N2EY
  10. WA6MHZ

    WA6MHZ Premium Subscriber QRZ Page

    I actually have 2 brand new meters here I bought just for this purpose. And the current panel is ugly and useless. SO that sounds like a good plan. Find some thick aluminum and make a new panel, which I can paint and letter with my professional labelmaking maching here at work. I am not happy how the back LED lighting came out either. It is not even and some of the meter face isn't lit. Very tough to make LED lighting equal what an old fashioned Incandescent bulb did.

    I just got back from the QCWA meeting, but it is way after 3PM and the sun is getting lower in the sky. SO I might hafta wait till next week to do anything more. I PROBABLY should just rip out the front panel and start over from there. I don't like the metering circuit I have either. Remember, I used a HM-102 meter modified to equal a SB-200 meter. Today, on Ebay, a real SB-200 meter of unknown condition went for (OMG!!!!) $78!!!!!!!!!!! So maybe my new non-Heathkit meters that are KNOWN GOOD will be a much better choice. There is room for a THIRD meter too, (grid current) since the bandswitch has been removed. I need to go to the Junkyard and find some metal for a new panel!
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