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75A 2 Restoration

Discussion in '"Boat Anchor" & Classic Equipment' started by K5HFG, Jul 12, 2018.

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  1. K5HFG

    K5HFG Ham Member QRZ Page

    This thread grew out of the thread titled Wanted: 51J 4 Power Transformer. The pictures show a 75A2 in rather good shape except for some mods that had previously been done. The mods will come out and the receiver will be restored to originality. (Hopefully ;)) Below are pictures showing as is condition.
     

    Attached Files:

  2. W5INC

    W5INC Ham Member QRZ Page

    Leaving the SSB mod in?
     
  3. K5HFG

    K5HFG Ham Member QRZ Page

    No. I am thinking all original to start. I am not much of a SSB operator.
     
  4. K9STH

    K9STH Ham Member Volunteer Moderator QRZ Page

    A product detector does work better for CW than the old diode detector.

    My particular 75A-2 was restored, and a product detector added, when it was owned by the previous owner, by Howard Mills. The product detector is installed in the NBFM adapter socket. The product detector definitely works better than the diode detector, for CW, that is original in my 75A-3. Now, my 75A-3 has the Collins Radio NBFM adapter installed. As such, adding a product detector to the 75A-3 would require considerably more effort.

    Glen, K9STH
     
  5. K5HFG

    K5HFG Ham Member QRZ Page

    Glen,
    I agree. But I need to return this receiver to original design and make sure it works before anything else. If I do put a SSB adapter in it, it would probably be the Tree Top circuits design. The bfo has been disconnected and I need to go over that and wire it back in. I now have the early model operating manual and schematic and have ordered replacement caps.
     
  6. W5INC

    W5INC Ham Member QRZ Page

    Somebody else is producing the SSB adapter for these radios, sought of looks like a Christmas Tree in it's design. On a Black plastic pole with some arms coming off it that is the mounting spot for the components. I looked on the Big auction site but it wasn't there. I will see if I can find it in my travels. Might be worth looking into if you decide to go that route, after getting the rig back to original shape.
     
    Last edited: Jul 14, 2018
  7. K9STH

    K9STH Ham Member Volunteer Moderator QRZ Page

    K1ZJH likes this.
  8. W5INC

    W5INC Ham Member QRZ Page

    I didn't know you make a product detector for this rigs Mr. Glen, you are a true Renaissance man in AR. I will keep the link and pass it on to others. Just like Campbell's soups, you know it's got to be good. :)
     
  9. K9STH

    K9STH Ham Member Volunteer Moderator QRZ Page

    The actual circuit was originally published in one of the older ARRL Single Sideband Manuals.

    I put the circuit, using a plug made from a defunct octal tube base, in my original 75A-2 back in the early 1970s. Several people wanted these for their 75A-2, 75A-2A, and 75A-3 receivers. So, I started making them.

    The earlier versions used germanium diodes but today I use Shottky diodes that work even better.

    The cost isn't for the parts because those are relatively low. It is the labor required to build and then "pot" the unit that adds up.

    Glen, K9STH
     
  10. W5INC

    W5INC Ham Member QRZ Page

    At the price that is attached to the link, it is a bargain IMO, Mr. Glenn. 38.00 seems more then reasonable for a well made, high performance product that is catering to this BA market. :)
     
    W7UUU likes this.

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