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HF amp - 4CX350FJ

Discussion in 'Home Brew' started by Panicos, Aug 19, 2011.

  1. Panicos

    Panicos Member

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    Hi there,

    I have decided that I start buiding a tube HF amplifier.
    It should have an output (SSB) NO more than 1Kw (say 700-800w). This will be my first HF amp.
    I have kept for many years (for future use...) four 4CX350FJ which I dont know if they are any good (externaly are in excellent condition).
    Q1. Is there a way to test these tubes (4CX350FJ) and know if they are any good before installing them on the amp?
    Q2. Are they a good choice or should I use different tube (e.g. 3-500Z)? Any suggestion is most welcome.
    Q3. Bearing in mind that I dont have much experience in such amps, would it be a good idea to built one from the scratch or buy an old cheap one rebuilt/restore it?

    Thanks for your time



    Panicos
     

  2. GnG8d

    GnG8d Well-Known Member

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    I'd definitely start with the 3-500z before attempting a tet.
     
  3. Panicos

    Panicos Member

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    I think I will follow your advise (y) and start with a triod. Any suggestions for tubes and diagrams?
     
  4. n0zna

    n0zna Digital master

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    i have a nice homade cx250 amp...and a 572b amp i made...tubes aew cheap on them
     
  5. BJ radionut

    BJ radionut Supporting Member and 6m addict

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    Easy Kilowatt Linear Amplifier

    New Page 1

    Good links to start with...
    There are Loads of info on the Heathkit SB-1000/HL-1000...Ameritron AL-80b...if you just search around...Take heed to all the safety info out there also...
    HF Tube type Amps can KILL you in an instant! So just be careful, think
    before you stick your hands/ and or tools in one even as building...
    One eye watering/burnt finger or other extremities experience could be your LAST!
    GL
    All the Best
    BJ

    Note added: I agree with 359...Triode first...3-500zg...GI7BT...4-400C...ETC...
     
    #5 BJ radionut, Aug 20, 2011
    Last edited: Aug 20, 2011
  6. Panicos

    Panicos Member

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    Many thanks for your help. The Ameritron AL80 design sounds a better idea since it uses only one 3-500 . I will search for the circuit.
     
  7. ElectronTubesRule

    ElectronTubesRule Active Member

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    They can be tested. If you do not have the gear I guarantee someone can test them.

    I would use one GS31 tube and another as a spare. You can do it in grounded grid which is super simple. You go with fixed bias if you not worried about AM effciency.....fixed bias is easiest using a zener diode but it will generate more heat and wear and tear when you run on AM. If you can deal with variable bias set up then that will be a better set up if you use AM as much as you use SSB.

    If you decide not to use AM at all you can get away with a much smaller power supply as well.

    The GS31 has conservative output rating of 1000 watts. If you run them with a stiff power supply I have seen some get as much as 2240 Watts Pep on AM so and 2400 on SSB but that is really pushing them hard.
     

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