Ameritron 811x

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

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  1. M0TRJ

    M0TRJ Ham Member QRZ Page

    Dont know if this helps but I put only the 2 NOS cetron valves in and swr showing on radio off scale wether 5w or 35w
     
  2. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    HI Simon,

    I read that date code as "December, '07" but regardless, the grids are directly grounded by rather lousy looking solder joints... but no matter, a bad grid resistor doesn't appear to be the problem. (It looks like non-factory mods have happened in there).

    We may be looking for a bad solder joint. You can also check out the bandswitch and make sure the wafers are in the correct place (like the grub screws have not slipped).

    There's not much that can be wrong in there. We're looking for a single point failure causing high SWR input, all bands.

    Can I post the pictures you sent?

    Can you take a few wider angle shots and post them? There appears to be some toast going on in there but I can't quite make it out.

    cheerios,
    Chris
     
    Last edited: Mar 9, 2018
  3. M0TRJ

    M0TRJ Ham Member QRZ Page

    yes please use pics i will have to dismantle everything to take more so maybe later
     
  4. KA9JLM

    KA9JLM Ham Member QRZ Page

    Without all of the tubes in the amp, You will most likely have to touch-up the input matching coils to bring the SWR down.

    The filament voltage may be a bit high too.

    Good Luck.
     
  5. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Well, maybe you can take a few more measurements with the ohmmeter before tearing the amp down.

    AL-811 9.jpg
    There could easily be a bad relay doing this, but you can check a few components easily enough.
    Measure less than an ohm from in to out (red circle). Measure a few to several ohms at the yellow circles (DC resistance of the inductors). Measure open at the greenies.

    All of that OK? Suspect a bad relay contact.

    AL-811 10.jpg
     
  6. G3YRO

    G3YRO Ham Member QRZ Page

    Although the relays they use are HORRIBLE - sealed, so you can't clean the contacts (and I've had to replace them a couple of times in these Amps), I can't see how it could be the relays causing this, because the SWR is fine straight through the Amp (ie in the Standby position), and drive is actually getting to the PA Valves OK.

    Simon you never answered my earlier questions:

    1. On transmit, but without any drive, what is the PA standing current?

    2. What about the Grid Current?

    3. With about 20 watts of Drive (the mismatch won't hurt your rig at this power) what power output do you get? And what does the PA Current and the Grid Current read?

    Answering these questions will help diagnosing the fault.

    Also . . . please confirm that this Amp was working OK, and this fault suddenly occured. (I ask this as it is easy to remove the back panel and re-assemble with the Input bandswitch out of sync with the front panel . . . but this can't be if you haven't had it apart.)

    Roger G3YRO
     
    Last edited: Mar 9, 2018
  7. M0TRJ

    M0TRJ Ham Member QRZ Page

    Sorry Roger my PC crashed been spending the day resetting it I have not had time to look but will tomorrow

    Thanks for your help

    Simon
     
  8. N1RND

    N1RND Ham Member QRZ Page

    Any luck Simon?
    Been watching this thread.
     
  9. M0TRJ

    M0TRJ Ham Member QRZ Page

    not yet am waiting for the new valves to rule out valve problems
     
  10. G3YRO

    G3YRO Ham Member QRZ Page

    OK . . . but it would be worth answering the above questions with the existing Valves . .

    Roger G3YRO
     

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