Heathkit Cheyenne power supply project

Discussion in 'Amplitude Modulation' started by N2DTS, Sep 2, 2021.

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  1. N2DTS

    N2DTS Ham Member QRZ Page

    I have a few idea's for winter radio projects and one is a robust power supply for my well working
    Cheyenne transmitter.
    I have tested it at 400 volts and it works well but only puts out 5 watts at that voltage.
    looking to make a 700 volt choke input supply and would need about a 1400 to 1500 volts center tapped
    transformer at about 150 to 200 ma.
    If anyone has one, or knows of a source, let me know.

    Other projects might be another higher powered screen modulator using something like a 6DQ6 as the catthode follower, triode connected. I use a triode connected 6l6 in another transmitter and it works fine but would like to try the sweep tube.
    It will drive three 4X150 tubes for 300 watts on 40, replacing my 200 watt setup using two 4X150's and a 6EW7 modulator.

    AnTec may make a transformer but I am unsure what model.
     
  2. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    Cheyenne's are great little rigs but I sold mine two years ago.

    I have an HT-37 fully functional power transformer that meets those specs above. It produced 900+ volts in circuit on Keyup. I also have the HT-37 PS choke if you need it. I don't need it.

    Below is the Modulator I used for my SG modulated 813 and 4-400 rig.

    Pheel

     

    Attached Files:

    Last edited: Sep 2, 2021
  3. W9GB

    W9GB Ham Member QRZ Page

    Heath MR-1 & MT-1
    Comanche & Cheyenne Mobile HF Twins

    Heathkit of the Month #10 ; November 2008
    by Bob Eckweiler, AF6C
    https://www.w6ze.org/Heathkit/Heathkit_010_MR1_MT1.pdf

    The Cheyenne (MT-1) mobile HF ham-band transmitter and
    the companion Comanche (MR-1) mobile HF ham-band receiver
    sold between 1959 and 1962.
    The Heathkit UT-1 (1960) and HP-20 (1961-63) were HV power supplies for Cheyenne (MT-1).
    The UT-1 was only offered for one (1) year, 1960.
    ==
    Improving AM Performance of the Heathkit MT-1 Cheyenne Transmitter
    based upon Electric Radio articles by Bill Breshears, WC3K, on improving the DX-60 audio.
    by Jeff Anderson, K6JCA
    December 10, 2009
    http://k6jca.blogspot.com/2009/12/improving-am-performance-of-heathkit-mt.html


    Heathkit HP-23A/B/C/E AC Power Supply Family
    includes UT-1 and HP-20 models

    Heathkit of the Month #26 ; February 2011
    by Bob Eckweiler, AF6C
    http://www.w6ze.org/Heathkit/Heathkit_026_HP23C.pdf
     
    Last edited: Sep 2, 2021
  4. KC2ZFA

    KC2ZFA Ham Member QRZ Page

  5. N2DTS

    N2DTS Ham Member QRZ Page

    I have the audio sounding very good, the rig puts out about 22 watts at 120% positive modulation.
    The drake supply I used puts about 720 volts on the HV and 300 on the low voltage.
    I found a 750 volt center tapped transformer and I could do full wave bridge using it.
    Had a long qso using it with Brian, N3TBW.
    The 300 volt buss had some hum on it, but the rig worked very well.
     
  6. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    There is a serious error in that schematic with the redlining.

    You never, never adjust the filament voltage to vary power. If he wanted to vary power he should have placed the 25k in series with the 6DE7 cathode pin 8, but even that method is not preferable.

    A preferable method is to use a voltage divider for the grid bias on the grid of Unit 2 as seen in the PDF because the voltage is more predictable and stable.

    Pheel



     

    Attached Files:

    Last edited: Sep 3, 2021
  7. N2DTS

    N2DTS Ham Member QRZ Page

    I assume its a mistake and it meant to be connected to the cathode.
     
  8. N2DTS

    N2DTS Ham Member QRZ Page

    What is RL2 doing, bias to grid unkeyed, 200+ volts positive in operation?
    200+ volts to the audio driver?? I guess there would be a cap in series, but that much positive
    voltage seems odd...


     
  9. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    I assume you are referring to the Cheyenne schematic in the file below? What is RL2?

    The 6DE7 first triode (6DE7 Unit 1) is converted to a Class A RC coupled audio amplifier with values determined from the tube curves. i.e., 200 Volts@5mA in this case which puts its operation into the linear region.

    https://frank.pocnet.net/sheets/106/6/6DE7.pdf

    A voltage divider, which is sourced from Unit 1's plate voltage sets the bias for the cathode follower (6DE7 Unit 2) via Rg4new. A capacitor couples Unit 1's audio to Unit 2's grid, audio which would have otherwise been "dropped" or attenuated by Rg2new. Rg4new is the grid resistor for Unit 2.

    One should always characterize the cathode follower one is using in order to determine its transfer characteristics in the circuit you intend to use.

    There are two versions, one modulator is non adjustable and the second allows adjustable power output.

    Like the HT-40, the Cheyenne is a good platform for modifications and upgrades.

    The clear advantage to the Cheyenne is that it has a well-designed and fairly stable VFO for a mobile unit.

    Or, were you referring to the 572B modulator?

    The 572B modulator modulator uses a relay to switch between two biases, as determined by characterization of the 572B as a cathode follower, and directly drives the screens with no CC time constants.

    Pheel





     

    Attached Files:

    Last edited: Sep 3, 2021
  10. W7TFO

    W7TFO Premium Subscriber QRZ Page

    Did you find any iron?

    If you have a 240V line in the shack, I've got you covered.

    Let me know,

    73DG
     

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