SB-220 Filter Capacitor replacement fit

Discussion in 'Amateur Radio Amplifiers' started by KD5YPH, Dec 17, 2015.

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  1. KD5YPH

    KD5YPH Ham Member QRZ Page

    I'm working on rebuilding a SB220 and ordered the ES4SB220 from Harbach in bare PCB form to replace the filter capacitor block. Last night I tried to install the board, but I can't get the rectangular bracket in place over the plastic spacers. The screws don't make it through the bottom holes and no amount of pushing on the bracket seems to help. Based on recommendations here and my own measurements, I used the following CDE cap: 381LX331M450A042. Diameter is 35mm which is what the openings measure so I'm really confused on why this isn't working. I'm looking for advice on enlarging the plastic capacitor holders to fit the new caps better, or on what to try to get them to fit as is.

    Thanks for the help!
     
  2. W1QJ

    W1QJ Ham Member QRZ Page

    Most newer snap in caps have the same diameter as the stock capacitors and if you used the right caps and assembled the board correctly everything should fit. With the whole network removed and on your bench, assemble all the plastic shells between the caps. Squeeze them like gripping a sandwich and make sure all the shells close up upon one another and there are no spaces. If you can squeeze it so the whole assembly is tight there is no reason why it won't fit. Make sure the board is not hitting the chassis or something. I am sure that Jeff from Harbach has filed tested the board to absolutely fool proof as long as you have used the correct caps. Also, check to see if the shells have been melted on the edges from heat produced by the original bleeders. When they melt the edges get rough and the shells may not fit properly. Another consideration is that there is a tolerance on the caps being soldered to the board. It almost pays to set up the caps in the shells and compress them with tape and then slip the board over the cap tabs and solder them while squeezed in the shells. This would make for a perfect fit. I designed a similar board some years ago and because my dimensions were off a tad bit, the whole thing never fit. There is little room for error. The screws are plenty long enough to catch under the chassis if the shells are compressed properly.
     
  3. KM1H

    KM1H Ham Member QRZ Page

    Those caps should fit snugly in the stock holders and stay put when you tighten down the aluminum "cage" No PC board needed and solder the equalizing resistors in place as the originals.

    Leave the bottom lip on the caps exposed otherwise it wont fit.

    Carl
     
  4. W9GB

    W9GB Ham Member QRZ Page

    Warren,

    Jeff covers this situation in Harbach Instructions (FB-220 v3.0)
    http://harbachelectronics.com/wp-content/uploads/2015/01/FB-220-v3.0.pdf
    • Press the electrolytic capacitors through both sets of plastic holders one capacitor at a time. Note proper orientation so they match the positive/negative pads on the PC board.
      NOTE: Depending on the thickness of the plastic coating on the electrolytic capacitors, you may have to enlarge the inner diameter of the holes slightly using a razor blade or razor knife. You should remove only enough from the inner diameter so that the capacitors fit very snugly. The plastic holders should be spaced so that the bottom holder is approximately 1” from the bottom of the capacitors and the top holder is approximately 2-1/2” above the bottom spacer. You may use a few beads of hot melt glue to affix the holders to the capacitors, but this is not required.
    image.jpeg image.jpeg
     
    Last edited: Dec 17, 2015
  5. KD5YPH

    KD5YPH Ham Member QRZ Page

    Thanks all. I'm thinking it's time to use a razor blade/knife. These are the stock spacers not the newer Harbach version. Does anyone have an idea on how long the screws are on the mounting bracket? I'm curious if this bracket has been "modified".
     
  6. KD5YPH

    KD5YPH Ham Member QRZ Page

    I tried shaving some of the holders down last night and I'll need some better method beyond a razor blade. Can anyone suggest another material I can machine into spacers? It looks like the Harbach kit includes teflon spacers? I'm also wondering if anyone else that has assembled the ES4SB220 can confirm which capacitors they used. Perhaps I just need to order 30mm versions.
     
  7. KA9JLM

    KA9JLM Ham Member QRZ Page

    Can you take pictures so we can see ?

    Why would a razor blade/knife be needed ? Hack jobs do not work good for me.

    Good Luck on your project.
     
  8. KM5FL

    KM5FL Ham Member QRZ Page

    Seems to me a dremel tool and a sanding drum would be a better idea..

    KM5FL
     
  9. KM1H

    KM1H Ham Member QRZ Page

    More like a regular drill and a sharp wire wheel as thats several inches per cap that has to be hacked and whacked in those holders. Id send the package back to Harbach. and do it the simple way I mentioned above.
     
  10. KD5YPH

    KD5YPH Ham Member QRZ Page

    Here are some photos to show what I'm working with.

    IMG_0075.jpg IMG_0076.jpg IMG_0074.jpg
     

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