first amp Gi-7b

Discussion in 'Homebrew and Kit Projects' started by SV2SBE, Oct 17, 2017.

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  1. SV2SBE

    SV2SBE Ham Member QRZ Page

    just to ask again,
    i made a dummy load at 100ohms like the tube input.
    so,can i use this dummy and test with my antenna analyzer the correct part values for the tuned input?or i have to use grid dip meter?
  2. SV2SBE

    SV2SBE Ham Member QRZ Page

    ok,after change some plans about the amplifier i decided to make it with two tubes.To make one and keep it and need another one in one years!!My main question is the HV transformer.Will a 800ma will be sufficient for the double tubes or make it 1 amp?i will
  3. KM1H

    KM1H Ham Member QRZ Page

    Here is an amp design spread sheet that is also popular with the commercial manufacturers from one of the Zed's own members. Ive relied on it for many years and have never been disappointed.
    and scroll own to
    Tube PA Design and Construction

    While the GI-7B family is popular since it is so cheap (most hams #1 requirement) it is a poor choice for SSB since the IMD even at the published Russian specs, is in the class of sweep tubes plus it gets worse when the HV and drive gets run up without any thought to the consequences. The original use was in pulsed UHF service (military radar, etc) where IMD was not a high requirement.

    It appears that as long as the wattmeter wiggles a lot it is good....10-4.

  4. SV2SBE

    SV2SBE Ham Member QRZ Page

    This is my first project amplifier.I have choosen these tubes for the cheap price as you say.I want to try them at digi modes like FT8.So i dont want to fry a good tube.Will keep them low on drive and HV and i think i will not have troubles with IMD.
  5. SV2SBE

    SV2SBE Ham Member QRZ Page


    parts for the RF compartment done!!!50% russian-50% US made!!air-vac are from Heathkit sb-220 and choke the classic one for all Ameritron.Russian army made sockets and now have to think what to use for cooling (i think axial fan will be low).The HV compartment is on the way.Finnaly i will use 2-2,1Kv at anode from a transformer with voltage doubler.Im making the board with the diodes and capacitors.Im thinking about 200mf will be enough to maintain a stable HV with the doubler.

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