Low recieive after unkeying!

Discussion in 'Amateur Radio Amplifiers' started by AC9EX, May 1, 2012.

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  1. AC9EX

    AC9EX Premium Subscriber QRZ Page

    I recently purchased a new (for me) Dentron Clipperton L. My setup is as follows: FT-950 - Clipperton L - SWR meter - Remote Coax switch - HY-Tower. I also have a RLB-11 optical isolator between the radio and the Clipperton L for keying circuit. With the amp online (operating) 500 watts, when I un-key the radio the radio has very low receive (low reading on the radio S-meter and low audio). If I set the amp in standby and key the radio again the receive comes back to normal! I tune the internal tuner on the radio before I set the amp to operate and the SWR is good on both the radio and the antenna, (it is very flat across the 20 meter band). Could this be an issue with the TX/RX relay in the amp? Or would it be RF? the amp is on a shelf right above the FT-950, so they are about 6" apart. Any help would be greatly appreciated! This is my first amplifier.
    Todd Beay
    KB9VUP :(
  2. AF6LJ

    AF6LJ Premium Subscriber QRZ Page

    I would clean the RX / TX relay with a non abrasive paper card like a business card soaked in contact cleaner.
  3. WA7PRC

    WA7PRC Ham Member QRZ Page

    The relay is "dry switching" and the NC (Normally Closed) contacts are oxided. The contacts can be cleaned w/o opening the cabinet. Switch a DC current simply and easily like Tom/W8JI suggests here.
  4. W1QJ

    W1QJ Ham Member QRZ Page

    YOU MUST NOT HAVE THE RADIO'S ANTENNA TUNER ENGAGED WHEN YOU USING AN AMPLIFIER!! SHUT THE RADIO'S ANTENNA OFF AND TRY AGAIN. Although this may not be your problem you still should not be using the antenna tuner. Answer this, When you turn the amp in standby and then hit the radio once again, does the antenna tuner retune? If it does, then what I say is your problem. If you have an antenna that is not resonant and you are using an antenna that needs a tuner, you will need an additional high power tuner now that you have an amp. The antenna tuner in the radio does you no good now as far as tuning the antenna.
  5. NZ9Y

    NZ9Y Premium Subscriber QRZ Page

    My money is on W1QJ. The rigs ATU is tuning to the input SWR of the amp on TX and then is way off from the antenna on RX. What is the antenna's SWR?

    Or not. I had the relay thing happen to me, twice.
  6. AG6K

    AG6K Ham Member QRZ Page

     It could easily be the RX contacts on the relay Todd. To find out, when the RX level is low try pushing the relay contacts together with the eraser end of a pencil. Sometimes the contacts need to be polished, sometimes the contact's leaf-arm needs to be bent to make the contacts wipe, sometimes the polarity to the relay's coil needs to be reversed.
  7. AF6LJ

    AF6LJ Premium Subscriber QRZ Page

    That is a good method.
    And will tend to keep hands away from dangerous voltages....
  8. W4AFB

    W4AFB Guest

    I would also start with cleaning the relay. Also check the wire coming off the relay to the SO-239, ive seen these wires fatigue from the relay opening and closing over the years. Turn off the antenna tuner also. If your tuned input SWR is high you have other issues that need to be addressed. One of the most important things to remember if your new to tube amps is watch the high voltage. Assume the whole amp is alive with 2800 volts.
  9. AC9EX

    AC9EX Premium Subscriber QRZ Page

    Thanks for all the suggestions!

    When I put the amp into standby and key the radio the SWR is 1.2/1. actually the SWR on the antenna is lower than the SWR of the amp before I tune the Internal antenna tuner in the radio. There is no tuner between the amp and antenna.
    I am thinking it is the relay also, I will clean the relay this weekend and reply to this thread to let everyone that was so kind to reply know what I found.
    When i originally went thru AIT radio tech school in the Army we worked on tube radios so I am not an entire novice at working around hi voltage, its just been a while! Guess I just dated myself! HI HI Thank you all very much for your replies!
    73 for now,
  10. WA7PRC

    WA7PRC Ham Member QRZ Page

    Classic symptoms of oxidized NC (Normally Closed) relay contacts. Open the amplifier and clean the contacts (with something non-abrasive) or, as I and W8JI suggest, just switch about an ampere of current thru the contacts. The latter is effective and easier than falling off a log.
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