Yaesu FT 847 married to Drake L4b ?

Discussion in 'Amateur Radio Amplifiers' started by W2VQY, Mar 1, 2018.

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  1. W2VQY

    W2VQY Ham Member QRZ Page

    Looking to upgrade to an amp for my FT 847.
    Have my eyes on a Drake L4b.
    In researching before the purchase, I have been going over references on setup.
    The L4b needs 3 inputs from the Tx: AGC(ALC), VOX, Tx input.
    The FT847 has available ALC(AGC), Tx Output, but no VOX, although there is a VOX switch on the front.

    Any comments???
  2. W1GCI

    W1GCI Ham Member QRZ Page

    You can get the manual for the L4B from BAMA. VOX refers to the relay in the L4B that puts it into transmit mode. What it expects from the 'exciter' is a pair of contacts that close on transmit. It's not referring to voice operated switch . The 847 has a connector with a separate switch for each frequency range - HF, 6, 2, 432. I believe these are relay contacts rather than solid state. Take a look at the manual.
  3. W2VQY

    W2VQY Ham Member QRZ Page

    The information above is what I have gathered from both manuals.
    The L4b is requiring these three inputs:
    Tx input
    The FT 847 has only two of these:
    Tx Output
  4. W1QJ

    W1QJ Ham Member QRZ Page

    VQY....The L4b really does not need ALC, you can skip that it is really not necessary. A 100 watt radio can not over drive the L4b so just forget about it. Then all you really need is the "VOX" which is really the wrong term they use. That VOX is really just a "ground on transmit" which you can get from the 847. Just check to see if the 847 can handle 24vdc at about 100ma which is about what the antenna relay draws on the L4b. And of course your input and output coax cables.
  5. W2VQY

    W2VQY Ham Member QRZ Page

    Okay now that makes some sense. The T/R control lines are transistor “open collector” circuits, capable of handling positive amplifier relay coil voltage of up to +24V DC and current of up to. 100 mA. Thanks for the info..
    Last edited: Mar 2, 2018
  6. K5RT

    K5RT Ham Member QRZ Page

    I would encourage you to purchase an amplifier interface in this application
  7. W2VQY

    W2VQY Ham Member QRZ Page

    Yes. Interface is on the list. I know Amertron makes one. I like to explore multiple options though, any suggestions?
  8. W1QJ

    W1QJ Ham Member QRZ Page

    W7ry and Harbach both make them
  9. W2VQY

    W2VQY Ham Member QRZ Page


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