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Looking at a COLLINS 75A4 RECEIVER , need advise

Discussion in '"Boat Anchor" & Classic Equipment' started by KB4MNG, Jun 14, 2019.

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  1. WB2GCR

    WB2GCR Ham Member QRZ Page

    Although it's heresy, you can take one or more Murata type ceramic filters, some
    transistors for level shifting and buffering and make a fairly great filter this way too.

    If you had a dead mechanical filter, you could open the case and hide the whole
    thing in that! :D
     
  2. KE0ZU

    KE0ZU Ham Member QRZ Page

    I got my SN 33XX -A4 with all three filters a couple months ago for $250. I think you need to do some looking, or bargining, or both. The pic is as received with no clean up done yet.

    [​IMG]
     
    Last edited: Jun 16, 2019
    W1BR, W1TRY and KD2ACO like this.
  3. W2VW

    W2VW Ham Member QRZ Page

    The reason usually has to do with the receiver being used for SWLing or actual communication on the amateur bands.

    Anyone who gets on the air on AM for any length of time is familiar with the benefit of the utility of steep selectivity skirts.
     
  4. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    ^^^ Amen^^^ :p
     
  5. KE0ZU

    KE0ZU Ham Member QRZ Page

    Cheap ceramic filters with decent skirts from Murata and others are available in a wide variety of bandwidths.
     
  6. KA9JLM

    KA9JLM Ham Member QRZ Page

    They do not normally die.

    Would you tell a buyer that you hide something to make it look original ?

    A butcher does that with ground meat.
     
  7. K5UJ

    K5UJ Ham Member QRZ Page

    All true except I wouldn't say the skirts are decent. They're not particularly steep compared to multi-pole xtal and ceramic filters. But a lot of what makes them acceptable depends on the kind of operating being done and the antenna and location. Uncongested band ragchewing and they're okay. CW with a lot of QRM not very good at all. W2VW is correct in that phone at night in an area of a lot of QRO AM and you want those vertical skirts and even a < 6 kc filter.
     
  8. KE0ZU

    KE0ZU Ham Member QRZ Page

    I am specifically talking about 6 element ceramic filters, which have 6/50dB shapes of about 2.5. Not as good as 6 element crystal filters, but MUCH cheaper, and also far better than typical L/C I.F. filters.
     
  9. W1BR

    W1BR Ham Member QRZ Page

    Collins mechanical filters of that era were typically around 100k impedance when resonated in parallel mode. Well suited for tube gear. Ceramic filters are low impedance devices and will need some impedance matching networks to work in those receivers.
     
  10. KE0ZU

    KE0ZU Ham Member QRZ Page

    True, and easily done.
     

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