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

    I have aquired a Heath SB-220 from the local HRO.
    The amplifier was placed on consignment and was owned by an SK. The amplifier appears to have been unused for some time, a long time as there is a bit of crud that has settled on the controls, It was last operated on twenty meters from the positions of the knobs and where the crud had settled. That's both good and bad as the amplifier will have to be carefully brought up on a variac and observations made for gas in the tubes. Speaking of tubes they appear to be original Emiac tubes, date code is 7501. The amplifier also has the one hundred sixty meter mod and a small transformer used to power the meter lamps, why this was done I am not sure.

    The workmenship is very good both the mod and the amplifier were built by someone who was skilled. Except for the addition of the transformer and a terminal strip where the wires for the meter lamps were moved to there is no obvious signs of rework. The fan needs to be removed and the motor cleaned and re-lubed before application of power.

    There are some notes that came with the amplifier that details tune up on one-sixty, and a note where new HV meter resistors were acquired for the HV meter divider string back in 1985, complete with the Heath SanDiego store's phone number.

    There are some modifications worth doing one is picking up a low voltage T/R relay, I prefer doing that over the soft key mods out there. The soft start mod would be nice also. I like the idea of having the amplifier on one-sixty however I am of two minds about how the mod was executed in this amplifier, more on that later.

    A word about modifications and how I feel about them is in order.
    Everybody has their own approach to customizing that peace of gear to meet their needs, or to bring it up to date, or whatever the reason. We do what is most comfortable for each of us, parts availability skill pressure to use many things play into the end result. With that said I am of two minds about keeping the one-sixty mod. Should I decide to keep the amplifier usable on-one sixty I will implement the modification in a different manner, if not I will just return the amplifier to it's original configuration. This decision will come after the level of functionality is ascertained. At this point this is a rehabilitation thread, and getting the amplifier to do what is does is my goal. After that we shall see what's next.

    In regards to pictures I would have already uploaded them save for one minor issue. The previous owner placed his name in several locations on the chassis using a rubber stamp. The pictures I have I will obscure the name before posting them to the internet.
    for now...
    [​IMG]
    More to follow.........
     
  2. K9ASE

    K9ASE XML Subscriber QRZ Page

    Nice find, I wish we had an HRO around here.
     
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Nice, Sue!

    Be careful working on that...remember there's MILLIONS of OHMS in there!:eek:

    I wonder why anyone would add a xfmr for pilot lamps. You sure it's not also wired to something else (like maybe he already did a low-voltage keying modification)?
     
  4. AF6LJ

    AF6LJ Ham Member QRZ Page

    I traced out the wiring, the twisted pair of brown wires that normally go to the terminal strip that supports the cold end of the filament choke have been moved to a separate terminal strip, the transformer secondary wires go there, the twisted pair of brown wires terminate at the terminal strip that the meter lights are connected to.

    I am going to pull one of the lamps today when I pull the fan, and see what they are.
     
  5. AF6LJ

    AF6LJ Ham Member QRZ Page

    I pulled the lamps from the meters, the lamps in the meters are #47.
    Now I could be wrong but as I remember that is what they are suppose to be, in spite of the lamps being fed from the filament supply.

    Also took the fan out and disassembled it cleaned it and re lubed it, spins freely now.

    The tubes have been removed and packed in a box for safe keeping for the time being.
     
  6. WA8ZYT

    WA8ZYT Ham Member QRZ Page

    What!!!???? Your not going to convert this to 6 meters??? How about a dual band 160/6 amp? Possibilities are endless.:cool:
     
  7. AF6LJ

    AF6LJ Ham Member QRZ Page

    That's good, I was thinking about a 144MHZ conversion then I sobered up. :)
    Been cleaning off the desk, not safe to work on something, anything with a bench that is too cluttered.

    And my bench was.
     
  8. W1BR

    W1BR Ham Member QRZ Page

    Nice find! I always thought the SB-220 had a lot of potential. I rebuilt mine last year and added nine band coverage and full QSK CW.

    Pete

    [​IMG]
    [​IMG]
     
  9. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Around 3000 Volts.
     
  10. WA7PRC

    WA7PRC Ham Member QRZ Page

    Yes, #47 (6.3V/150mA). My '220 still has the lamps in it when I got it, ca 1975. When run on 5V, they last a LONG time.
    If you ever need to replace the fan motor, the one sold by a well-known source can be purchased much cheaper from Grainger, pn 4M070.
    In any case, you can realize more airflow and less noise by adding a shroud, as shown by David K5DBS here.
    VA7JW has a 39 page list of SB220 modifications. I found the 2-speed fan interesting but mine will be controlled "automagically" by PTT and a thermal switch. W7RY sells a bare PCB that, when stuffed, drives fast vacuum & reed T/R relays, and provides electronically switched & regulated bias.
     
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