32s-1 and a Gonset G76 winter projects?

Discussion in 'Amplitude Modulation' started by N2DTS, Sep 13, 2021.

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  1. N2DTS

    N2DTS Ham Member QRZ Page

    I scored a very cheap nice but dirty 32s-1 transmitter that I may turn into a screen modulated rig.
    It cleaned up very nice and I am waiting for the 11 pin octal plug to test it, the tubes all tested good.

    I also got a like new stock Gonset G76 which is my 4th one, I may keep this one, its very clean.
    I plan on some light audio mods and may try installing a 5 watt IC chip audio amplifier in it to get the audio off the driver and improve fidelity on RX. I did that is the past and it sounded great.
    Rectify some filament power to power it.

    Such a neat AM rig.
    N2EY and W8KHK like this.
  2. W8KHK

    W8KHK Ham Member QRZ Page

    Brett, I assume that is the same Amphenol 11-pin connector the Heath SB and HW line used for power. If that is the case, I have NOS (Never Obliterated with Solder) both male and female. Let me know if you need one, or both, and the shell for the cable, and I will put it in the mail to you.

    73, Rick
  3. N2DTS

    N2DTS Ham Member QRZ Page

    I already ordered connectors for it and a few spare tubes I do not have in my spares.
    Thanks for the offer!
    I have a bunch of the male side, and one female but it only has 4 pins in it...

    On a separate issue, the 32s-1 uses a 700 Hz audio osc to make the CW.
    I do not think it would be a good idea to screen modulate it with a 700 hz tone as the carrier.

    Unbalance the modulator?
  4. W8KHK

    W8KHK Ham Member QRZ Page

    I am assuming, without looking at the schematic, that the balanced modulator is fed 700 cps to generate the carrier in CW, which shifts the carrier 700 cps from where it would be without the audio modulation. If the balanced modulator is truly balanced, with good carrier suppression, and the opposite sideband is suppressed by the filter, then the resulting signal at the final will simply be an unmodulated carrier. So it should be possible to screen modulate the final with no concern for how the carrier was created. If you just unbalance the modulator and retain the 700 cps oscillator, then you would be transmitting an SSB signal of 700 cps, with insufficient carrier suppression.

    That said, there is also the issue of the frequency readout being offset due to the 700 cps modulation. It would be prudent to study the mixing formula, including the VFO or PTO, whichever is used for the main tuning oscillator, to determine what change might be needed to allow the dial readout to match the actual carrier frequency. If the 700 cps oscillator is suppressed, and the balanced modulator is unbalanced, then the carrier frequency will of course move 700 cps, but the dial still may not read out the actual carrier frequency.

    Perhaps using a frequency counter to measure the unmodulated drive signal would be more practical than changing a mixer crystal or heterodyne crystal to synchronize the dial readout with the actual transmit frequency.

    I suppose a greater concern when screen modulation this rig is the need for additional cooling, as the final tube dissipation would be much greater than when the final is used for either CW or SSB.
  5. N2DTS

    N2DTS Ham Member QRZ Page

    Yes, fun experiments to try!
    I figure about 25 watts carrier, but the only? AM 32s-1?
    Or just an exciter for bigger rigs (no modulation)?
  6. N2EY

    N2EY XML Subscriber QRZ Page

    If it were me - and it's not - I'd use it as an exciter. I'd also modify how it does CW.

    Here's why:

    A) Collins tried the audio-injection method of CW generation in the KWM-2 and 32S-1.

    In theory, it works fine.

    In practice, it doesn't, because:

    1) The balanced modulator must stay in perfect balance

    2) The unwanted-sideband rejection must be excellent

    3) The audio oscillator must generate a perfect sine wave, and the audio chain and balanced modulator must be distortion-free.

    4) Everything must stay that way indefinitely, because otherwise you have multiple carriers generated (spurs).

    They did this rather than have a second carrier crystal for CW, which is how practically every other rigmaker did it. They finally saw the light and dropped audio-injection in the 32S-3.

    B) The S-line was designed for SSB, so there isn't a lot of the "head room" normally found in AM transmitters - both for the 100% duty cycle of AM and for the modulation peaks.

    So it seems to me that the 32S-1 could have the CW generation system changed, and then it could become a really sweet exciter for an AM plate-modulated rig.


    73 de Jim, N2EY
    N4WLL and K5UJ like this.
  7. N2DTS

    N2DTS Ham Member QRZ Page

    Yes, I know it was bad on CW and find it odd that Collins would build something so screwed up.
    I think the audio tone generator will go and I will see what can be done without it.

    Adding a screen modulator is no problem and its a pair of 6146 tubes so should do about 25 watts carrier without melt down.
    I will not be using the Collins power supply.

    It would be interesting to see if I could use the audio generator tube socket for the screen modulator and have everything built in.
  8. KE0ZU

    KE0ZU Ham Member QRZ Page

    I've got an S1 and would be very interested in following your posts when you get yours on the bench.

    Although an entirely different subject, I did convert an old filter SSB rig to AM with good results.
  9. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    See Page 39 of the schematics, follow the PA Disable line. Quite a few component value changes would be needed for SG modulation.

    V11 is used in two functions, so I would guess, no.

  10. N2DTS

    N2DTS Ham Member QRZ Page

    At the moment, I can not get anything out of it.
    Sometimes the PTT works but I get no drive.
    It was sold as blows fuse, shich was a bypass cap wire shorting to the frame.

    I need to print the manual out and do a step by step check.

    The G76 is also been a chore also.
    The transmitter works very well, the receiver had a bunch of silly mods done to it that make no sense.
    I corrected a number of those and it was working well but dies after playing for 10 minutes.
    1 bad tube, a 27 ohm resistor in the dual diode filament connection that hosed things up.

    N2EY likes this.

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