[Milsurplus] MO/ MAK

[WA5CAB at cs.com]

Interesting.  SOP in most of the military sets (with plate modulation) is 
to have the PHONE-CW switch or a relay controlled by it short the choke or 
the secondary of the modulation transformer when the switch is set to CW.  I 
never gave any thought to your method but that may have been easier to add 
than a relay.

Robert Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480

In a message dated 01/23/2016 16:48:48 PM Central Standard Time, 
duvallddennis at gmail.com writes: 
> 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
> 
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