[Milsurplus] [MRCA] [MMRCG] GRC-106 AME problem

[Meir Ben-Dror WF2U]

Ray, and all who replied so far,

Thanks for the replies and input.

I don't have a second transceiver, but thinking of getting one.
It works fine in all modes except AM.
What threw me off is that the "tested" 1A5 module (transmitter IF/audio) I swapped the original, which works fine in all modes, except AM, also does the same thing, but works in all the other modes. When I ordered it from Fair Radio, I specifically asked to test it on AM as well.
The first thing, before I go through the APP/APC settings is to connect an RF step attenuator between the RT-834 output and the amplifier input, to set and measure the drive level that won't trip the overload, hoping that the problem is as simple as that, and it's not some kind of spike introduced into the exciter output from another fault when switching to transmit in the AM mode.

73, Meir WF2U
Landrum, SC


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On Jan 4, 2021, 9:53 AM, at 9:53 AM, Ray Fantini <rafantini at salisbury.edu> wrote:
>Is it working correctly in SSB? You should see the meter on the
>receiver exciter modulate with voice in SSB transmit. The APC/PPC pots
>under the little plate may be dirty but that will also affect your
>SSB/CW and FSK operation, if all that's working you will see more power
>output in CW/FSK then in SSB or AM. The receiver exciter only need to
>put out 100 Mw for full power on the amplifier and if the meter on the
>receiver exciter pegs you are way overdriving the amplifier and that's
>not a good thing.
>Don't you have a second receiver exciter with the 122 shelter? Did you
>try that with the amplifier? The amplifier pumps PPC back into the
>receiver exciter but if its working in SSB/CW that's all good.
>
>Ray F/KA3EKH
>
>
>From: MMRCG at groups.io <MMRCG at groups.io> On Behalf Of Meir Ben-Dror WF2U
>via groups.io
>Sent: Sunday, January 3, 2021 7:50 PM
>To: MMRCG at groups.io; Military Radio Collectors Association
><mrca at mailman.qth.net>; Armyradios <main at Army-Radios.groups.io>;
>Milsurplus <milsurplus at mailman.qth.net>
>Subject: [MMRCG] GRC-106 AME problem
>
>CAUTION: This email originated from outside of Salisbury University.
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>HNY all,
>
>I wonder whether anyone experienced a problem with trying to transmit
>on AM (actually it's AME) with the radio. My receiver/exciter is the
>RT-834. The system tunes, loads up and transmits (and receives)
>normally in all modes, with rated power, except when I'm attempting to
>transmit on AM, the amplifier kicks off at overload. The exciter meter
>pegs, and the amp center meter set on PA cathode current kicks up above
>the normal current momentarily as the amp kicks off. It is immediately
>resettable to Tune mode, where it works normally in all modes and the
>normal tuning carrier output. I suspected the 1A5 module (transmitter
>IF and audio), and I got a tested one from Fair Radio. I put it in and
>it does the same thing. I thought maybe the mode switch has a problem,
>but visually it looks OK and after applying contact cleaner just in
>case, it does the same thing.
>It looks like the exciter sends a spike into the amp when pressing the
>PTT only on AM (does the same on VOX as well) and that puts the amp in
>overload condition.
>I was even thinking that maybe the radio has a modification to prevent
>it from transmitting AM, but no ham messed with it before I bought the
>GRC-122 shelter complete with all the installed equipment directly from
>a surplus dealer's lot about 20 years ago. Everything in the shelter is
>still installed as I got it, and I operate the radio in there
>periodically. I never tried to use it on AM before the last few days,
>and I never had issues with it in sporadic use on SSB and CW.
>
>Any input is appreciated.
>
>Thanks,
>
>73, Meir WF2U
>Landrum, SC
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