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TX: What does the LOAD, PLATE, & DRIVE knobs actually control?

Discussion in 'Electronic Design' started by billcalley, Apr 8, 2007.

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  1. billcalley

    billcalley Guest

    Hi All,

    I know *how* to tune the finals of a "hybrid" HF transceiver, but I
    cannot find schematics of the exact circuits -- or even a good
    explanation -- of exactly *what* components are being tuned inside the
    transceiver itself. With tube transceivers, what exactly does each
    control do? (I.E: the LOAD, PLATE, and DRIVE controls in, lets say, a
    Kenwood TS line). Are these controls attached to the output pie
    network capacitors and inductor of the PA? (Like a "mini"
    transmatch). If so, which control is attached to which component?
    And does anyone know of any drawings or diagrams for this?

    Thanks for any clarifications!

  2. Tom Bruhns

    Tom Bruhns Guest

    Hi Bill,

    This is a better question to ask over in or
    the like. But... The drive control most likely tunes the stages that
    supply RF to the power amplifier's grid. The network that couples the
    power amplifier's plate circuit to the RF output connector is almost
    certainly a PI network, with fixed series inductor selected per band,
    but the shunt capacitors at the plate and the output ends are
    variables, labeled PLATE and LOAD (or "LOADING").

    Do a Google search for "Kenwood TS-520S schematic" and you should turn
    up one. You can probably find manuals for others in that line. You
    may find it interesting to simulate the PI network in Spice or RFSim99
    or some similar program.

  3. Tim Wescott

    Tim Wescott Guest

    Plate and load are connected to the final pi network, yes. "Band"
    switches the final coil, among other things.

    Drive controls the tuning of the final grid circuit (and drive tube
    plate). Plate controls the capacitor that's connected (possibly through
    a coupling cap) to the final plate, and load controls the capacitor
    that's attached to the antenna.

    You peak the drive, dip the plate, and adjust load to get the plate
    current you want.

    My TS-520 came with a schematic -- didn't yours?


    Tim Wescott
    Wescott Design Services

    Posting from Google? See

    Do you need to implement control loops in software?
    "Applied Control Theory for Embedded Systems" gives you just what it says.
    See details at
  4. billcalley

    billcalley Guest

    Thanks Tim, thanks Tom. Your explanations helps a lot, but the
    real TS-520S schems I find on the Web are a little too "real" and
    complex for me. (IE: They are not 'instructional' enough, diagram and
    clarity-wise, for me to really get a very clear idea as to what
    exactly is going on in the PA section).


  5. John Fields

    John Fields Guest

  6. MassiveProng

    MassiveProng Guest

    It really is in his best interest. Just getting the answer from
    someone wouldn't do much good.
  7. SFC

    SFC Guest

    Load - antenna coupling/matching
    Plate- tunes the network of the tubes anode
    Drive- tunes the network of the tubes grid

  8. billcalley

    billcalley Guest

    Thanks for the great info guys! The exact concept of where the TX
    tuning controls contacted the different parts of the tube circuits is
    what confused me (I'm aware of how matching circuits work). I had
    also looked through the ARRL Handbook (and the Web) before I asked the
    question here, but I did not see a circuit drawing or a satisfying
    description of the answer to my question at all, but maybe I just
    missed it.

    Thanks again,


  9. There are a lot of transmitter schematics on the BAMA website. Some
    complete ham radio manuals, as well.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
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