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SB-220 Find

Discussion in 'Amateur Radio Amplifiers' started by AF6LJ, Dec 19, 2012.

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  1. AF6LJ

    AF6LJ Ham Member QRZ Page

    Keep in mind the SB-220 is an 80-10 meter amp.
    Although it can be modified for one-sixty it is an involved proposition.
    My Sb-220 came to me with a one-sixty mod, and I chose to remove it and move on with rehabilitating the amplifier.
    To rehabilitate in this case means to restore, improve, modify or restore but not to stock condition.
     
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    That's why starting from scratch with a homebrew project is so nice: You needn't comply with a form factor or available space...you make your own space.

    The HV caps for my 4-1000A, for example, cost about $25 total. They're just four 4uF oil filled 5kV caps, purchased surplus from Fair Radio. Locally, Apex has the same stuff, but when I built that amp I didn't live in L.A., I was living in NJ and Apex was too far away for me.

    They're pretty big and maybe ugly, but they get the job done. No circuit board parameters to limit choices, they just bolt to a chassis using the metal clamps they come with.

    They're also oil filled and can handle thermal extremes.

    My 6m amp article can actually be modified to any band, because "most of the work" is the power supply. Once you build that, you can make an amp for any band or bands. The RF part is easier.
     
  3. AF6LJ

    AF6LJ Ham Member QRZ Page

    Very true and if someone had access to some decent metal working tools the amplifier could be built with plug in modules that contained both input and output circuits. Each module optimized for the band of interest.
    Your amplifier design was well executed, I would love to see that sometime.
     
  4. WA7PRC

    WA7PRC Ham Member QRZ Page

    Not really. Sue has made some wise choices. To save some money, avoid the easy Harbach route.

    I made the expensive Harbach mistake only once. Most of their stuff is OK but you can easily do better on many parts.

    The resistors I used are mentioned here... Vishay VR68-series, rated WAY over 1KV each. Digi-Key has 'em. Mouser has something similar for mo money.

    The box for my 160m GS35b amplifier HVPS needed to be 18"x18"x12" to accommodate the > 4KVA xfmr I rewound, and a nice 1H/800mA/7.5Ω/15KV choke I traded for. I have the box assembled; when I have time, I'm prepping it for paint & lettering.

    The GS35b compares closely to the 3CX1500, at a fraction of the cost. After I (finally) get my 160m RF deck online, I may start on one for 6m and/or 2m.
     
  5. AF6LJ

    AF6LJ Ham Member QRZ Page

    The current plan is to continue this project next month, I'll lay my hands on the last parts for the QSK mod and then the plastic covered wiring will be replaced.
    Stay Tuned.........
     
  6. AF6LJ

    AF6LJ Ham Member QRZ Page

    Took the time this morning to solve a minor mystery.
    When I had the front panel off in order to remove the one hundred sixty mods. when I reassembled Oscar I went though and checked the output on all bands, and I found that I had high input VSWR on ten meters.

    Well this morning while checking out the amplifier into a dummy load I decided to try and see if the input circuit was tuned for twelve meters, it was, mystery solved.

    I have also decided after giving it much consideration and research on the subject, I am going to directly ground the grids of the 3-500Zs the next time I am inside Oscar. :)
     
  7. WA7PRC

    WA7PRC Ham Member QRZ Page

    This is how I did that on my SB-220:
    [​IMG]
    I used soft copper sheet (0.020" thick). Hardware is #4-40.
    I bent the socket terminal lugs up at the edge of the socket,
    and formed the copper strips up and over the lugs, and soldered.
    You can see that, using short & wide copper strip, series XL is minimized.
     
  8. AF6LJ

    AF6LJ Ham Member QRZ Page

    My plan is to do something very similar to that.
     
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