Heathkit MT-1 Cheyenne transmitter.

Discussion in 'Amplitude Modulation' started by N2DTS, Jan 29, 2020.

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  1. N2DTS

    N2DTS Ham Member QRZ Page

    Picked up another one of these on ebay, in very good shape.
    I had one before and put the WA1QIX dx60 mods in it for real hifi audio and was amazed at how well it worked.
    I sold it for some reason, but this one is in better shape.

    It had a bad (shorted) 6146 tube in it but everything else seems good.
    I found a few loose nuts, cleaned the dust out of it and tried iit on a power supply I had around.
    VFO: very stable (I mean real stable) and accurate, just like the last one.
    Plenty of power out on CW.
    AM sounds quite nasty stock.
    I removed everything in the audio section and will add the WA1QIX mods.

    I may need to build up a good supply for the radio, the one I was using had the low voltage too low.
    I may be able to change that.
    The transmitter seemed to work with 12 vac into it, the relay worked, but that first stage mic preamp may need DC on the filaments to not have a lot of hum in the audio.

    The MT-1 seems to be one of Heathkits better designs, if I designed it, it would likely be close to the same with just the audio/screen modulator improvements.
    Its got a very nice tuning VFO with a big scale and no backlash or slop in the knob.
    Its got a built in T/R relay.
    Its smaller and light.
    Its got PTT.
    Just buld up a robust supply and stick it under the desk out of the way.

    Tube lineup:
    6au6 vfo,
    oa2 vr regulator,
    6cl6 buffer/multiplier,
    5763 driver,
    6146 output,
    12ax7 preamp, 6de7 screen modulator.

    I find the VFO's in these things amazing, I powered the thing up, set the flex 5000 to zero beat and the MT-1 did not move more then 20 Hz from cold.
    As received, so far as I have tried, 40 meters is 5 Khz off per the slide rule dial.

    One annoyance is the band knob is hard to turn, even after lubing the parts, its a smallish chromed knob
    that is slippery, the chrome looks REAL nice but its slick...

    With the modulator mods, its a great rig to feed into an amp, the carrier level is adjustable.
    Peak power will be something around 50 watts and you can run any power from about 3 watts to 15 watts carrier.
    All the parts seem good for the power and voltage levels.
    I think I ran the last one at 700 or more volts on the plate for something like 20 watts out.

    It will also make a nice exciter/driver for a big rig...

    Unlike some Heathkit stuff, it is a sensible design.
     
  2. W7KNX

    W7KNX Ham Member QRZ Page

    Excellent idea for a project. Maybe you could post some pics when you're finished.

    Jeff W7KNX
     
  3. N2DTS

    N2DTS Ham Member QRZ Page

    [​IMG]
    [​IMG]

    Got it done, it needs some detail work but it functions well.
    I removed that loading shaft to pack a lot of parts in a small space.
    Carrier control is on the back below the CW key.
    My power supply was only doing 400 volts so the carrier power output was only 10 watts.

    The first stage of audio needs some adjustment, too much output I think, causing some distortion, or maybe its the low voltage...

    I think I will need to make a power supply for it giving the correct voltages .
     
    KE4OH and W7KNX like this.
  4. N2DTS

    N2DTS Ham Member QRZ Page

    Hooked up an old Drake supply, the MT-1 puts out 20 watts carrier with over 120% modulation in the positive direction.
    Sounds good also.
    720 volts on the high voltage.
    At 20 watts the 6146 is running hot but I do not see any color on the plate.
    Likely better to run it at 10 or 15 watts carrier out on phone.

    I just need to change the PTT relay power to 12 volts DC to keep 60 cycles out of the mic cable and to tweak the dial calibration on all the bands.
     
  5. N2DTS

    N2DTS Ham Member QRZ Page

    Got the 12 vdc ptt setup working, cleaned the front and knobs up, and it just needs a slight calibration.

    Nice radio, no odd tube types, no odd design choices, a really good mechanical design.
    Its got the right stuff, a handy spot switch, tuning and loading, a drive control, built in T/R relay, audio gain control.
    It would be fun to put a 4X150/4cx250 into it in place of the 6146 and run ranger power output levels.
     
  6. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    I had an MT-1 Cheyenne in college (mid 1960s) that I used as a fixed station transmitter at my fraternity house my sophomore year. After getting married my junior year, I used it at my house and then mobile with a Motorola T44AAV power supply. Then, modified it to use with a Heath SB-10 SSB adapter. The VFO design is close to that in the TX-1 Apache and it worked very well. Finally, gave it to any employee who had just gotten his Novice Class license.

    I acquired 2-each "basket case" MT-1 units a while back and was able to get a complete transmitter from the remains.

    001a.jpg

    I do have the Heath HP-20 power supply that was designed to be used with the MT-1 and also have the SSB version, the HX-20, that I use with the same power supply.

    One thing is that, on most MT-1 units, the band switch knob is hard to turn. Adding a longer 6-32 machine screw, or other lever type extension, makes changing bands much easier. The HX-20 has the same problem!

    Glen, K9STH
     
  7. N2DTS

    N2DTS Ham Member QRZ Page

    Neat little rigs.
    In testing, I found my zener string open, its supposed to be 36 volts (three 12 volts in series) and need to order more.
     

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