[R-390] R-390A power switch

[Glenn Little]

MOVs normally failed shorted.
When properly installed in a surge suppressor, they have a chemical 
fuse in series with the MOV with the fuse held in close contact with 
the MOV by glass tape.

73
Glenn
WB4UIV


At 06:12 PM 1/23/2014, Roy Morgan wrote:

>On Jan 23, 2014, at 4:29 PM, Chris Farley <kc9ieq at yahoo.com> wrote:
>
> > ...  Perhaps using a Y safety capacitor instead of a normal disc 
> ceramic would be beneficial?
>
>Good idea.  I will after a while make another order to 
>justradios.com who sell these caps.  If that cap failed with the 
>switch open, it would mean an amp of current through the 100 ohm 
>resistor - smoke would come out for sure.
>
> >  Inrush MOV's are good devices too,
>
>I wonder if they make too much heat in the place they are often 
>installed: near the fuse holder.
>
> > but don't have the best reliability long-term.
>
>Do they short or open up?
>
> > Using a Triac to power the rig might also be a worthwile consideration,
>
>Or even a relay.  There has been published a modification to the 
>Collins S-Line 516F-2 Power supply to install a relay for the 
>job.  The power switch is at the back of  a volume control in the 
>transmitter itself, and is both failing due to the inrush overload 
>and very hard to find.
>
>Roy
>
>Roy Morgan
>RoyMorgan at alum.mit.edu
>K1LKY Since 1958
>
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