HW 23A Transmit Problem

Discussion in '"Boat Anchor" & Classic Equipment' started by W1FMX, May 14, 2021.

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  1. W1FMX

    W1FMX Ham Member QRZ Page

    Still working on the HW-32A that I have been restoring. It works fine in receive and when put into "tune" mode - bias setting and power is at correct level when switch is set for Operate-Tune; there is output on a wattmeter when in tune. So, it tunes up as it should.

    The problem occurs when a microphone is connected and the microphone's PTT button pressed. With the HW 32A's slide switch is set to "Operate Tune", as the microphone's button is pressed, the rig's meter peaks suddenly at 20/9 and then drops to S4 level and stays there while the button is held down. But, there is no response to talking into the microphone - no output on a wattmeter, either. Then, when the microphone's button is released, the meter pegs to the left (below zero) and then comes back to rest at zero.

    The microphone is o.k. - tried another as well - same problem happens. Checked shielded cable from mic jack - seems o.k. and its connections are good. V1 and V2 check out o.k. on tester.

    Would appreciate any thoughts about what might be the problem here.

    Tnx.
    Bill
    N1LJQ
     
  2. N4HZ

    N4HZ Ham Member QRZ Page

     
  3. N4HZ

    N4HZ Ham Member QRZ Page

    Hi Bill:
    I've just finished getting my HW12A in shape. The 32A is very similar so I'll be glad to do checks for you on this one if it helps. If I understand correctly with the radio in tune position you have output power but you didn't say how much. As far as your meter going to +20 upon keying the mic and going below zero upon letting off the mic button that is normal. With a mic connected and the panel slider switch in bias position pushing the mic button should show the needle resting at the little triangle mark on the meter ( with no speaking into the mic) indicating that you have bias correctly set . I think you indicated that is what you're seeing.
    It sounds as if you're just not getting audio from the mic as you suspected as well. I'd suggest this:

    Put the radio on a dummy load and the frequency dial to mid range. Leave the slider switch in the "bias" position and put the function switch in the "Tune" position. Assuming you are getting some power output on your power meter adjust the front panel "Final Tune" pot for a dip in the meter reading. Now adjust the rear panel "Tune Level" pot for maximum power meter reading. You should be able to see good power of 100 watts or so depending on condition of tubes and other components. If you can't reach 80-100 watts then that should be fixed first.

    Those tests just help me confirm what I think you have already found. If the radio passes those tests then on to the next step. I'm assuming you do not have an audio generator which would be the correct way to proceed. However, at least with my radio I can rotate the function switch to PTT position, insert a wire ( be sure to make good contact) into I think it's pin 2 of the mic connector then key the radio by touching the end of the wire to the mic shell. ( ground) Insert another wire into the audio pin of the connector ( pin1) and touch the end of this wire with your fingers while the radio is keyed. ( Mic level pot turned up) Just the hum of touching the wire will drive my radio to full power output. Anyway if you do get power output with this test then that would indicate to me an incorrect mic is being used, incorrect mic connection or something like that. If you still have no output with the finger test then I'd troubleshoot voltages, wiring, etc around the early audio stages. A disclaimer here because we never know the experience level of those who might read this. With the radio on it's side the 800 volt high voltage not to mention lower voltages are out in the open for a dropped probe or slipped finger to touch so I'm always cautious and never work when tired nor do I get in a hurry.

    Anyway those are my thoughts. Hope it might help a little. I'll leave my HW12A on the bench and will be glad to benchmark if there is something you'd like me to check.
    Thanks for helping keep these classic Heathkits on the air. I have a few Heathkits and use them about as much as I do my Icom 7300. It's like driving a classic car on Sunday afternoons.

    Roger
    N4HZ
     
    N4FZ likes this.
  4. N4HZ

    N4HZ Ham Member QRZ Page

    Bill....that's a dip in the radio panel meter
     
  5. W1FMX

    W1FMX Ham Member QRZ Page

    Hi, Roger.

    Thank you for writing such a detailed set of guidelines - I really appreciate that. Sorry, but I thought I had replied before, but don't see it here, so it must have gotten lost in the ether!

    The radio is now working! Thank you for your help!

    Have fun with your HW-12A!

    73's,

    Bill
    N1LJQ
     
    N4FZ likes this.
  6. W5RKL

    W5RKL Ham Member QRZ Page

    The "FINAL TUNE" control is not a pot but rather it is a variable capacitor.

    After adjusting the final amplifier's 50ma no RF drive idling current, perform the simple
    transmitter loading:

    Adjust the VFO for the operating frequency.
    Set the FUNCTION switch to the TUNE position and the meter switch to the OPERATE TUNE setting.
    Adjust the FINAL TUNE control for a "Maximum" meter indication, not a DIP in meter indication.
    Set the FUNCTION switch to PTT.
    Connect a microphone to the MIC socket and press the microphone PTT button.
    While speaking in a normal voice level an inch or two from the microphone, adjust the MIC gain for a
    couple of S units "upward" peaks on the meter indicating max power output.

    If the meter switch is set to BIAS then the meter indicates the final amp plate current. Adjusting the MIC
    control for proper voice transmissions should produce meter peaks no higher than S6 when speaking at a
    normal voice level into the microphone. If peaks are higher than S6, adjust the MIC gain control CCW
    so the peaks indicate no higher than S6 .

    Perform the transmitter loading with the transceiver connected to a 50-ohm dummy load after which
    the transceiver is connected to the antenna.

    An Heathkit HO-10 or SB-610 or similar type monitor scope can be connected between the transceiver
    and the antenna to watch your output signal so you don't overdrive the speech amplifier when adjusting
    the MIC gain.

    73
    Mike W5RKL
     
  7. W1FMX

    W1FMX Ham Member QRZ Page

    Hi, Mike.

    Thank you for the clear explanation for loading up the HW-32A. I appreciate your taking the time to write that.

    By the way, the original problem that I had had me really stumped - it was that I could tune the rig, but not use the microphone - when I pressed the PTT button, nothing happened. On a hunch, after looking at the schematic, I wondered if it might be a resistor or if there was a problem with the balanced modulator. So, I changed out the 4 germanium diodes (then also replaced CR60 as I was on a roll!) in the radio and the one 10K resistor at the MIC jack which was over 20% above specified value and after doing that, it solved the problem. Now the rig works fine. In retrospect, I should have tried doing just one thing at a time to see where the problem really was...

    73's,

    Bill
    N1LJQ
     
  8. W5RKL

    W5RKL Ham Member QRZ Page

    Bill,

    Glad to hear your HW-32A is now working. Here are a few comments about tests you can perform.

    Based on what you said about pressing the PTT button and "nothing happened", I would assume the relays are
    not energizing by pressing the microphone PTT button. There's a simple test you can do. Remove the microphone
    from the radio, set the FUNCTION switch to PTT, and short pin "2" on the microphone socket to the ground.
    If the relays energize then the problem is in the microphone PTT switch/wiring or plug.

    You can test resistor R202 (10K 1/2W) using a scope connected to the grid pin 2 of the speech amp V1A. If
    the microphone element is not wired through the PTT switch, in receive speak into the microphone and
    the scope connected to pin 2 of V1A should display the microphone's audio signal. If the microphone
    element is wired through the PTT switch then VOX won't work with that microphone and you won't
    see any audio at pin 2 of V1A.

    I can't say with any certainty that replacing the 4 diodes in the BM fixed your problem. I suspect the
    CAR NULL adjustment would fail if one or more BM diodes were bad.


    73
    Mike W5RKL
     
  9. W1FMX

    W1FMX Ham Member QRZ Page

    Hi, Mike.

    Thank you for suggesting the tests for the rig and for your thoughts about the BM diodes - that is very helpful.

    The microphone I had connected has an interesting story. It is an old Turner +2 that I got in 1970 and used with an HW-100 that I built at the time. As a new General licensee at that time, I somehow thought the pre-amp in the MIC would give me a more powerful signal. Well, anyway, the MIC got packed away and survived a number of moves and had not been used in 50 years. While rummaging through the attic, I was surprised to find it as I did not even remember having it. So, I put a 9v. battery into the Turner+2 and connected it to an HW-12A that I was using a few months ago and the MIC worked . I couldn't believe it still worked well after years of being in our attic.

    Thanks again!

    73's,

    Bill
    N1LJQ
     

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