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Collins 75S-3B Optional CW Filters

Discussion in '"Boat Anchor" & Classic Equipment' started by WZ6F, May 30, 2021.

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  1. WZ6F

    WZ6F Ham Member QRZ Page


    I did a search, but maybe just missed them.

    Wondering, could someone tell me please the options I have for filling the 2 CW filter vacant positions? Ideally, I would like a solution that gives the performance (or thereabouts) without waiting and paying for the original Collins filters to become available. It just has the SSB filter option filled currently (926-9427 filter).

    Some potential questions I considered whose answers may help (feel free to consider/skip - I am sure all of you know more than I do on this receiver!):
    - Are there any currently available manufacturers selling something that will work?
    - Are there other known compatible filters out there (e.g. IF frequency, impedances, etc.) with potentially just some soldering (e.g. other Collins filters not specifically made for the 75S-3B/C)?
    - Not that I would, but is the 75S-1 filter 200Hz filter compatible with the 75S-3B with soldering it in? I have two of the 75S receivers currently (the 75S-1 and 75S-3B).

    Both of the 75S receivers I have work very well in terms of sensitivity, selectivity especially for the 75S-1 with the 200Hz filter, ergonomics, etc. Ideally, I would like to add an AM filter as well to the 3B, but need to do some research first.

    Note: I have noticed for SSB that using the receiver's rejection tuning in conjunction with external DSP (JPS NIR-12 Noise And Interference Reducer) brings the lower frequency noise down a good amount. It is worth using in some cases and will experiment more for optimal settings (especially for CW). Considering though what I heard in terms of the DSP improving CW, I definitely want to see what I can find in filling in the optional filter positions.

    Thanks for looking!
  2. WA1GXC

    WA1GXC Ham Member QRZ Page

    The Collins Collectors' Association has a website with much information, most resources open to all, even non-paying members.
    You can search their archives online --The question comes up a lot. Also, you may post an inquiry to buy, I believe, on their discussion site.
    If you haven't accessed them before , it's a great resource.

    I bought a 75S-3C (same receiver) in 1985 and acquired a new 200kHz compatible filter for CW manufactured by Fox-Tango (no longer in
    business), drop-in plug-in and supposedly electrically equivalent. It wasn't. The impedance was way-off and even with changing input and output
    capacitances in the receiver's filter circuit there's more signal path loss than there should be. If I had to do it over again I'd get the narrowest
    Collins 455kHz mechanical filter I could acquire or a real Collins OEM crystal filter. Collins left the filter business quite a while ago and you may easily
    pay $150-175 for a filter-- 1/3 the price of a receiver in good condition these days. Prices have tanked. Too many Amateurs going to Sunset Acres
    or ham heaven.

    Good luck.
  3. WZ6F

    WZ6F Ham Member QRZ Page

    Great response, thank you. I will check out the CCA. I am surprised that it looks like I will probably need to go back to the original filters considering what you said for which their price agrees - ie in demand so alternatives are probably hard/close to impossible to find. I do like the Collins equipment, considering the tradeoffs I care about- my station of choice. Very sad about the older Collins generation passing away. I bet a lot of us have the Elmers to which we are grateful and miss. I expect to be looking for that 200 or 300Hz filter shortly. Thanks again for the response!
    WA1GXC likes this.

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