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Thread: NEC CQ-301 AMP

  1. #1

    Default NEC CQ-301 AMP

    Hi All
    I have bought a pair of QY 4-400 very cheap and i was wondering if i can use them in my nec cq-301 Linear My Linear is the same as a Heathkit 220,so i need Help.I waqnted to know what the standing carrent is four 2 3-500zg and also for the 2 QY 4-400 .My Manual does not tell me that at the moment the standing currant for 2 3-500zg is 0.06.
    So any Help Please
    Many Thanks
    73 de Wolf G4ssx

  2. #2


    The NEC CQ-301 manual can be found at MODS.DK

    It is only 12 pages with schematic, so it really is a minimal document.

    Cosmetically, the amplifier looks somewhat like the Kenwood TL-922(A) HF amplifier, which also uses dual 3-500Z glass RF tubes.

    Nullius in verba

  3. #3


    Wolf -

    Here is an earlier Q&A about this same question!;wap2

    The 4-400 is a TETRODE glass tube, and normally requires a screen supply (voltage).
    Your NEC amplifier does NOT have that screen supply and the 5-pin socket
    would require rewiring to operate as a true TETRODE.

    The 3-500Z and the 3-400 are TRIODE glass RF tubes. Your NEC CQ-301 was designed for a TRIODE.

    Electrically they can be interchanged, you need to check socket wiring, and height clearances.
    Current draw (mA) can be an issue, it depends on your NEC CQ-301 power supply.
    4-400a tubes have been used interchangeably with 3-400, 4-250, 3-500z tubes.
    While the QY 4-400 may work -- it is not ideal.

    Go buy the proper 3-500Z glass RF tubes for your NEC HF amplifier.
    Given the age of this amplifier, you may be well advised to check / replace the HV electrolytic capacitors.

    Last edited by W9GB; 04-04-2012 at 10:57 PM.
    Nullius in verba

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