ETO ALPHA-77 (1972 - 1977)

Discussion in 'Amateur Radio Amplifiers' started by HB9TPT, Sep 13, 2017.

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  1. HB9TPT

    HB9TPT Ham Member QRZ Page

    i am looking for a connoisseur of ETO ALPHA 77.
    My problem is the plate current of the tube.
    It goes up to about 220mA, with no transmitter connected.
    On the control board I have replaced Q4 and Q5 as well as the Zener diode D13.
    Q4 is now an equivalent NTE154 instead of an original 2N5184.
    I hope someone can give me some advice.
    73 de Guido, HB9TPT
    hb9tpt@gmail.com
     
  2. W1QJ

    W1QJ Ham Member QRZ Page

    It sounds like the amp is in transmit and drawing idle current. This means something in the keying circuit is making the amp think it wants to be in transmit. Either that or there is a tube problem.
     
  3. RICHS

    RICHS QRZ Member

    The amplifier is in a key down state when it shouldn't be or the (cutoff) bias voltage is wrong or the tube is shot or something weird. What's the grid current if anything. Do you have any indication that the amp might be oscillating?
     
  4. HB9TPT

    HB9TPT Ham Member QRZ Page

    W1QJ, thank for answer.

    the plate current rises without connecting the transmitter or key.
    input and output relay works well.

    And thank to Richs
    The amplifier otherwise works normally and delivers full performance. Net is in order, the fuse does not burn through .... hi
    If the disk current is at 220mA without a probe, there is no output at the antenna output.
     
  5. HB9TPT

    HB9TPT Ham Member QRZ Page

    I suspect a problem with the tube. Insofar as a symtom is possible
     
  6. W1QJ

    W1QJ Ham Member QRZ Page

    Any current being drawn in standby by is usually a bad tube indication.
     
  7. W9GB

    W9GB Ham Member QRZ Page

    ETO Alpha PA-77 : Manual
    http://www.radiomanual.info/schemi/ACC_PA/ETO_Alpha_77_serv_user_W0UN_AE0Q.pdf

    -- W8IDL history --
    The ETO Alpha PA-77 series of HF amplifiers started out as the Alpha 70V using the 3CV1500A7 vapor cooled tube, with ten (10) air cooled amplifiers built (70A) using the 3CX1000A7 tube.

    The Alpha 77 came next, built in the 70V cabinet, with the 8877 air cooled tube.
    The next revision was to build the 77D and 77Dx in a larger and better enclosure.
    The 77Dx has it all: vacuum variable tuning capacitor with turns counter, vacuum T/R relay, RadioSwitch heavy duty bandswitch, excellent metering, elegant electronic signal and keying controls, and anodized aluminum sheet metal work.

    Dick Einhorn built two special ETO Alpha PA-77 amplifiers for Don Wallace, W6AM, that had a turns-counter vacuum variable for the loading capacitor.
     
    Last edited: Sep 14, 2017 at 1:45 AM
  8. HB9TPT

    HB9TPT Ham Member QRZ Page

    yes the PA has been built fantastically. Super US quality. If they only worked properly, I would be happy.
    But I still have the ACOM 1000, which also makes a good job ...
     
  9. HB9TPT

    HB9TPT Ham Member QRZ Page

    At the same time I should sell the PA as defective?
    What is such a thing worth as no work Amplifire?
    The components are very preciousor ...
    better than individual parts sell or simply keep as a souvenir?
     
  10. W9GB

    W9GB Ham Member QRZ Page

    Guido -
    IF you are happy with your Acom 1000,
    THEN you can sell the ALPHA PA-77 as non-working (bad tube) and needs work.
    --
    You could contact Dick Byrd, N4UQ to determine
    if he is aware of European buyers interested in this model.
    TransAtlantic Air Cargo rates prohibitive, unless you work for airlines (or military/gov't).
    http://www.n4uq.com/
     

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