[Milsurplus] MO/ MAK

[Dennis DuVall]

Well, turns out the problem was not "modulation flashover" per-se.  The radios use a Heising modulation scheme and the modulation choke is mounted 
down on the power supply chassis.  Ten henry reactor here with 200ma passing through it and NO snubbing provisions provided for key-up.  The thing had to 
come up on it’s own with a “spark gap” somewhere in the wiring and in the case of one of my units this was a quarter inch gap between the lead to the PA plate cap and 
a nearby mounting bracket.  Clearly visible in my case.  However, the cable connection to the power supply and the choke was routed through two sets of the
Ampthenol 12 pin “octal” connectors popular at the time.  VERY close spacing here and the thus a very likely place for the necessary arc-over to occur.  This happens a 
few times, a carbon track forms and the next time the radio is keyed and modulated the connector self destructs…..

I fixed the problem by delaying turn-off of the modulator tubes which then absorbed the kick.  Worked perfectly.  First and only time I’ve seen a screw=up 
like that in a military rig, though.  Neat little radios BTW which work rather well. once the fix is in place  Twenty-five watts honest output, modulate fully and the 
receiver is hot and selective enough to accommodate 10 kHz AM channel spacing.  Used these with VERY good results at the Field Days I used to run down at 
Ft. MacArthur.

Dennis D.  W7QHO
Glendale, CA

************
> On Jan 23, 2016, at 10:05 AM, Hubert Miller <kargo_cult at msn.com> wrote:
> 
> 
> I assumed this was for general vehicles use as well as assault vehicles, amphibs. The manual cites specs with antenna down to one 4 ft.
> section, which reminds me of similar specs for the No. 19 tank radio. The modulator connector flashover is a hard to rationalize design
> failure mode,  it seems. I saw a ComCo ad that talked about the civilian market for this and other ComCo boat radios after the war, but
> the MO/ MAK would never have competed on price against less expensive, skimpier products, and it would have gotten a bad name in
> short order with that vulnerability.
> -Hue
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