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KWM-2 Low Power Out

Discussion in '"Boat Anchor" & Classic Equipment' started by W3TA, Oct 17, 2021.

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  1. W3TA

    W3TA Ham Member QRZ Page

    Or am I expecting too much?

    Just finished getting life back into my KWM-2. RX works very well but I do believe the TX power out is a bit "soft".

    Here's what I get:

    80m (3.6mHz) - 85w with 200mA plate current.

    40m (7.0 mHz) - 90w and 190mA plate

    20m (14.0 mHz) - 70w and 200mA plate

    15m (21.0 mHz) - 65w and 200mA plate

    10m (28.5 mHz) - 40w and 200mA plate

    Note, the plate current doesn't go above 200mA. Was expecting more like 230mA.

    I performed the RF alignment and things definitly needed to be peaked, but this is what I ended up with.

    I understand the typical roll of on 15m and 10m but all seem a tad soft.

    6146B's in the final. On the tube tester (Hickok 539B) they are both at 6500 and the roll chart says 7000.

    6LC6 driver tests fine.

    My first KWM-2. I have a32S-3B and it defintly puts out more power, maybe a tube swap is in order (just thought of that as I'm typing.......)

    Other thoughts?

    Tom
    W3TA
     
  2. KW4H

    KW4H Platinum Subscriber Platinum Subscriber QRZ Page

    Are those power numbers while transmitting into a dummy load?
     
  3. W3TA

    W3TA Ham Member QRZ Page

    Yes. Sorry, left out that detail
     
  4. KW4H

    KW4H Platinum Subscriber Platinum Subscriber QRZ Page

    I'd do a couple of relatively simple things first. One -- check the power supply and tube voltages. And two -- do a quick run-through using an ohmmeter and check to see if any important resistors have drifted.

    73 - Steve
     
  5. W3TA

    W3TA Ham Member QRZ Page

    Did the resistance checks before applying power and did a spot check on voltages. HV hovers around 80010v and drops to 775 when keyed.

    V9, V10 grid voltage - chart says -6ov but I'm measuring -48v. The -70v coming in is good and I checked R115, R116 and R117 - all within tolerance.

    Tom
    W3TA
     
  6. K8CCA

    K8CCA Ham Member QRZ Page

    Have the caps on the 516F-2 power supply been updated? 2 of mine had puked out thier guys.
     
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    With 200mA Ip it sounds like you likely have sufficient drive on the "bad" bands, but out of curiosity, what grid current is indicated when you only get 40W output on 10m?

    And, if you watch GRID current (not plate!) and adjust the PA TUNING, do you see a nice peak in GRID current as you tune the tank through resonance?
     
  8. W3TA

    W3TA Ham Member QRZ Page

    Yes. Power supply has been updated with one of the new(er) fancy circuit boards. Also has additional dropping resistor for the screen voltage.

    I have another tube 516F-2 with good caps and get the same results.

    I have also gone through the KWM-2 and replaced the electrolytics before starting this adventure.
     
    KL7KN likes this.
  9. W3TA

    W3TA Ham Member QRZ Page

    The grid does have a nice sharp peak. I do run out of room on the plate tuning on 10m though...........

    I'll tinker some more tonight and report back

    Tom
    W3TA
     
  10. KW4H

    KW4H Platinum Subscriber Platinum Subscriber QRZ Page

    Following this with great interest. I don't have a KWM-2 but I'm addicted to these puzzles and the causes for them. It's the result of years of electronics experience and training -- my mind is warped and I'm fascinated by badly-behaved electronics. :p
     

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