Need help with AN762-140

Discussion in 'Homebrew and Kit Projects' started by AF7OS, May 2, 2016.

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  1. AF7OS

    AF7OS Ham Member QRZ Page

    I'm building a AN762-140 from Communication Concepts, INC. They don't answer email or return phone calls so if you are wanted help from them forget it. If I knew how bad their support was before I had started, I would have gone somewhere else. I have the amp built and did the voltage tests before putting in the RF transformers per the directions. Everything was perfect. Put in the transformers, was trying the set the idle amps when I couldn't get a reading and the heat sink was just heating up. Self Oscillation? When I called, no return call. Email? same. Anyone here have any ideas. Called out ARRL labs because they recommended them and they said try here. Please help.
     
  2. NW2K

    NW2K Ham Member QRZ Page

    CCI supplies components to hams that want to build their own amps based on the Motorola app notes and engineering bulletins. I don't think they offer troubleshooting services.

    Here's another place to try for information, The Amps Reflector:

    http://lists.contesting.com/archives//html/Amps/
     
  3. PA0WV

    PA0WV Ham Member QRZ Page

    This is not a kit for beginners. It is just a bundle of components, matched transistors and a print,

    You have to know what you are doing.

    You have to wind the transformers exactly according to specifications, interchanging 2 connections (winding direction) make the circuit oscillating. Check for that with a scope without supply of RF to the input terminals of the circuit and the DC supply switched in. When you do not have a scope try with a diodedetector and a moving coil meter after that. (capacitor 0.1 uF to collector, in series wit a 100K resistor to ground. Look at measurements chapter in ARRL handbook, or antenna handbook for simple measurement circuits of RF voltage)

    Of course you have to make sure that you did not interchange resistors with different values, that you did not make any short circuits during soldering, that your electrolytic capacitors
    are not wire-interchanged, and finally that the regulator IC is not 180 degree wrong positioned. Those are the typical kit builders mistakes, made in a hurry to complete the kit in a record time.

    Try to adjust the bias on the transistors to make the quiescent current according to the class B (nearly zero) that will hold your transistor horses. Measure the current the DC supply is providing to the circuit.

    Transistors warm up in class A and AB due to quiescent collector current
     
    Last edited: Jun 3, 2016
  4. KA9JLM

    KA9JLM Ham Member QRZ Page

    I did notice the transistor appears to be mounted upside down.

    That could be a problem if you mount it properly.

    Good Luck.
     
    Last edited: Jun 3, 2016

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