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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

    An L-7 is a nice amplifier, I wanted one of these because I had repaired one before and thought they were a good value for the money. Besides it has American made tubes. :)
  2. WA7PRC

    WA7PRC Ham Member QRZ Page

    Oscar's new front panel looks good. :cool:
  3. AF6LJ

    AF6LJ Ham Member QRZ Page

    I am pleased, now time to russle up some parts for some Spring power supply work. :)
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I don't know what kind of PS work you need to do, but if you need "stuff," let me know.

    I have tons of PS components.

    Did you ever use all the Kapton tape?:eek:
  5. AF6LJ

    AF6LJ Ham Member QRZ Page

    I haven't used it all but I have used a few feet. :)

    I'll keep you in mind.
    I found my meter resistors and the main thing I need will be wire, the PVC wire is old and the insulation is hard.
    I have a hold on further rework until I get the wire I need to (in the correct colors) to replace it as I go.
    They way the front panel is wired (and it's by the book) makes working on anything to do with what is in front of the amp a royal pain....
    It's a simple job to make a wiring harness so the front panel can be sat beside the amplifier while work on that aria can be easily done, and it will look nicer when its done.
  6. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    If you are rebuilding the power supply, I strongly suggest replacing the rectifier diodes with 1N5408 diodes. They are cheap and are 3-ampere diodes @ 1000-volts.

    I keep a stock of 1N5408 diodes on hand and use them for power supplies for transmitters with more than around 250-watts to 300-watts output.

    Glen, K9STH
  7. AF6LJ

    AF6LJ Ham Member QRZ Page

    I have the required number of 1N5408s waiting in the box of Oscar stuff.
    Tomorrow a new fan motor will accompany them.
    I have hardware for additions such as a soft key module, should I decide to buy a pre-made kit, to keep the kit all US standard hardware. (I hate mixed US / metric mods it disrespects the original design).
    Saturday I am going shopping for parts at the local surplus store, the main thing I need is wire of the appropriate colors. I have everything else to make a harness, and two ways to go with that since I have a spool of lacing tape a peace of wood and a bunch of finishing nails. (it's very tempting)

    Finding filter caps with lugs on them of the right value and voltage rating is difficult.
    I'm tempted to spend the $130.00 on the Harbash kit since the caps fit the same holders and bracket.
    It does come with higher value bleeder resistors. and everything is neatly mounted to a PC board and slides right into the same location as the original caps.
    They just don't make caps like they use to.....
  8. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    I usually use the "snap in" type of electrolytic capacitors mounted on perf-board. You do have to slightly enlarge the holes through which the pins go using either a small diameter drill bit or an Xacto knife with a #11 blade. The hole spacing is correct but the diameter is just too small. After pushing the pins through the perf-board, bend them over and that makes a very secure mount.

    I have found that the perf-board from Radio Shack works very well as well as being inexpensive. There are not that many things that are really cheap at Radio Shack but perf-board and aluminum mini-boxes are definitely a bargain at Radio Shack.

    Glen, K9STH
  9. WA7PRC

    WA7PRC Ham Member QRZ Page

    Hi Sue,

    You may recall axial case rectifiers release most of their heat via their leads. Longer leads = better heat transfer.

    An external relay driver can be used with any amplifier. However, I like Jim W7RY's QSK board, since it contains electronic/adjustable bias regulation & control, as well as control of fast relays for QSK. At the very least, it's a good idea to insert 100 to 200 ohms of R in series with the SB220 ANT RELAY jack to tame the ≈6A current pulse from C52 (0.02uF) that happens when going from RX to TX.

    I like your attention to detail regarding the wiring though, a remarked schematic works well too.

    Before Harbach existed, I sourced replacement electrolytics for my SB220. Heathkit's #25-224 200uF/450V electrolytic was 3-15/16" (100mm) L x 1-3/8" (35mm) OD. Today, you can use Vishay "159 PUL-SI" series Low-ESR capacitors (datasheet). You want 1.378"/35mm OD, and can use the plastic holders Heath supplied (no perf board). Mouser and Digi-Key have various choices (220uF and up @ 450V) for around $10 and up. They have snap-in terminals.

    With a lot more capacitance, you'll want to use step-start. W7RY has a good one here.
  10. AH6RR

    AH6RR Ham Member QRZ Page


    I have been buying Silver plated Teflon coated wire off of eBay for a while now and almost all the wire in my SB-220 is that. You can not always find the correct solid color wire so I use a wire that has the original color in one of the stripes on the wire, sure it is more costly but it will take the heat 10 times better. My amp already had the Harbach Filter Caps in it when I got it, I know they are pricey but you do not have to search all over to find some that fit correctly. I have repaired 3 other 220's that had leaking filter caps with the Harbach kit. And as Bryan said the step-start is the way to go along with a soft key.
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