WHAT??? ANOTHER SB-220????!!!!!!!!!!!!!

Discussion in 'Amateur Radio Amplifiers' started by WA6MHZ, Jul 31, 2017.

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  1. WA7PRC

    WA7PRC Ham Member QRZ Page

    Pat @WA6MHZ already has one. OTOH, with HF propagation on upper HF going mostly dormant for the next few years, a 160m conversion/addition would make more sense for him.
     
    AF6LJ likes this.
  2. WA6MHZ

    WA6MHZ Subscriber QRZ Page

    MY DRAKE L7 already covers 160!! I used it to work the CLIPPERTON IS DXPEDITION a few years back, pumping 1000 Watts into the Cushcrudd R7!!! Yes it SMOKED IT, but I got the contact and I now have Clipperton confirmed on 160!! (I still have yet to work USA on 160!!)
     
  3. AF6LJ

    AF6LJ Ham Member QRZ Page

    Maybe I can arrange a contact on One--Sixty for you ;)
     
  4. AF6LJ

    AF6LJ Ham Member QRZ Page

  5. WA6MHZ

    WA6MHZ Subscriber QRZ Page

    we need to see what is smoked or still good. Sue has great reservations about the Tuning cap and tank circuit.
     
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  6. WA6MHZ

    WA6MHZ Subscriber QRZ Page

    Todays adventure in SB-220 repair had us pull the front panel
    20170801_063211.jpg
    I clipped out the wires to the panel and will be adding a quick disconnect connector like I did on the SB-226. This will make installation easier and troubleshooting feasible

    One suggested mod is to put back to back diodes across the meter elements. HERE Is how the CLOWN who modded this amp did his diodes. Anyone see a problem?
    20170801_073007.jpg
    I should replace all the solid wire with flexible 22 gauge stranded teflon wire. I will have a pigtail of teflon wires coming from the front panel to the connector that interfaces the chassis. Solid wire tends to break under stress.
    Another area of interest is the 120V power supply terminal strip. It was broken in half.
    20170801_064841.jpg
    That was removed and fixed with my MIRACLE JB WELD!!!
    20170801_071552.jpg
    now good as new!
    20170801_072719.jpg
    So we went on to other considerations.
    (continued)
     
  7. AF6LJ

    AF6LJ Ham Member QRZ Page

    The guy had the right idea on the meter
    If you use one diode the meter will never go past two thirds scale.

    Lets do the math...
    The plate shunt resistor is a one ohm resistor.
    .7 amps is typical for for an SB-220 (maybe a little more)
    One diode conducts at .6V
    So if we have .7A flowing through a 1 ohm resistor we have .7V
    If we clamp the meter with a diode that limits the voltage across the meter to .6V.
    SO
    You need two diodes in series and you only need to put them in one direction.

    I just noticed he has those diodes the wrong direction...
    They should be facing in one direction not cathode to cathode.With the cathode toward the "-" side of the meter.
    DAH...
     
  8. AF6LJ

    AF6LJ Ham Member QRZ Page

  9. WA6MHZ

    WA6MHZ Subscriber QRZ Page

    The diode board was yanked
    20170801_064507.jpg
    It is still unknown why the CLOWN disconnected the plate meter, as it works just fine.
    As we can see, there is a funny board that subs as the Zener. it is 8 diodes in series. He also added a 10 ohm 10W resistor on the HV output to the tubes.
    So now it is time to check the caps.
    20170801_063511.jpg
    the nuts on the bottom were loosened so the clamping plates will free up the caps. I pulled one and here is what i found
    20170801_071115.jpg
    we will let the experts guess the date code. It could be OCTOBER 1981, which would say these are the original caps
    Here is a view of the tube socket bottoms. All that nonsense will be TORN OUT and the GRID directly grounded
    20170801_064809.jpg
    not sure what the 150 ohmers on the filament pins are for, but they can probably go too.
    Here is the antenna relay, WHICH will be relaced with a W7RY vacuum relay setup AFTER the amp is working
    20170801_064820.jpg
    So it was time to replace the 220V plug with a 110V plug. I did so after inspecting the wiring for proper wiring
    here is the power switch and CW/SSB switch.
    20170801_064827.jpg
    OK lets plug it in!!!
    TO MY GREAT DELIGHT, the fan spun quietly and all low voltages looked fine. 5.45VAC was measured on the Tube socket pins.
    Not having a meter I dare test the 900V with, that was not tested. But I did switch the SSB/CW switch back and forth and all looked well. I saw 29VAC difference between the windings. It is ASSUMED the HV will be just fine once the caps are replaced and the diode board redone.
    So I would say we are good to go. NO SHORTS or catasphrophic failure seen.

    I will ASSUME the reason the CLOWN disconnected the AC wires was cuz the breakers blew when he tried to run 220VAC into with the jumpers set for 110VAC.
    The Tube condition is still unknown. WIll need to get a pair of Parasitic Suppressor for them!
     
    AF6LJ likes this.
  10. WA6MHZ

    WA6MHZ Subscriber QRZ Page

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