Ameritron 811x

Discussion in 'Amateur Radio Amplifiers' started by M0TRJ, Mar 2, 2018.

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  1. M0TRJ

    M0TRJ Ham Member QRZ Page

    Hi all hoping for some advice.

    I had both fuses blow on amp and when i took cover off found one tube blown glass was broken one had a filament gone so to be safe i replaced them all.


    put fuses in and it powered up ok so tuned antenna with my tuner, tuned amp, swr on radio TS-590SG was 1:1 tuner showed 1:1

    all's well i thought until i transmit with amp, swr very high and output power down yet tuner shows swr 1:1

    There's obviously something awry but what any suggestions please

    73

    Simon
     
  2. K6BSU

    K6BSU Ham Member QRZ Page

    Did you connect the ALC line? Could be the ALC is causing the driver Tx to go to low power.
     
  3. M0TRJ

    M0TRJ Ham Member QRZ Page

    No i dont use an alc lead the connections are the same as they were before replacing the three tubes i had no swr problems only since the issue occured
     
  4. G0JUR

    G0JUR Ham Member QRZ Page

    where is the high swr?on the input to the amp?
    if so then something has gone wrong with the input circuitry
    does this happen on all bands? or just one.
     
  5. M0TRJ

    M0TRJ Ham Member QRZ Page

    it happens on all bands i hope its an easy fix as i said if the amp is on but in standby then swr is good as soon as i put into xmit then swr on radio is high but tuner still shows 1:1
     
  6. G0JUR

    G0JUR Ham Member QRZ Page

    I take it you mean the tuner after the amp?
    if the swr is high in the radio then input circuits are either fauilty or out of tune.
    Unfortunately i am not familiar with the ameritron circuitry.
    will have a look on net see if I can find the schematic for one.
     
  7. G0JUR

    G0JUR Ham Member QRZ Page

    Ok have seen a schematic it could be something simple like a dirty relay contact or something in the input tuned circuits faulty.
    Unfortunately as its a valve amplifier working internally is not something that should be attempted by the inexperienced
    How much experience have you with these things?
     
  8. M0TRJ

    M0TRJ Ham Member QRZ Page

    I thought you might have guessed by the question HI HI. I have the lead to drain the capacitors and have looked at the simple things never thought of a dirty relay is that a carbon paper job to clean contacts
     
  9. G0JUR

    G0JUR Ham Member QRZ Page

    Not sure, never looked inside one, if its an open relay or the cover comes off then blotting paper and switch cleaner should work
    A better way is to electrically clean them but I suspect that may be out of your expertise to construct the circuit to do it.

    here is a link to the amp designers pages it gives some info on common problems with these amps
    https://www.w8ji.com/ameritron_811h_572_amplifier_trouble_shooting.htm

    read section 11 of the troubleshooting guide.

    apparently weak valves can cause yoyur issue.
     
  10. M0TRJ

    M0TRJ Ham Member QRZ Page

    Thanks Neill will digest
     

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