[Milsurplus] ARC-5/SCR-274 Receiver HV

[Michael Hanz]

There is no appreciable downside, Ken.  It's been documented numerous 
times on the ARC-5 (and probably this list as well), but it's been a 
number of years since anyone asked.  The fundamental reason for the high 
voltage is a single function - you need some oomph to drive a bunch of 
headphones in a multiplace aircraft.  The 12A6 will keep amplifying as 
you lower the B+, but it won't quit - the power output just goes down.  
A number of us (including Dave Stinson) have even run them on 24vdc B+ 
without losing too much, but you do need a bit more to keep the AVC 
working.  My solution was to transplant a AN/AIC-10 interphone amplifier 
dynamotor on a discarded command set dynamotor mounting plate.  Same 
physical size, and puts out 170 vdc with 28vdc in.  I always run my 
equipment with 24vdc, and that lowers the loaded output voltage to about 
160vdc.

- Mike  KC4TOS

On 9/7/2025 10:23 AM, Ken Kinderman wrote:
> Has anyone had experince with receiver HV lower than the nominal 235 
> VDC dynamotor output? I like to run everything at or slighly below 
> ratings. Not interested in squeezing out every last watt from the 
> transmitters, etc.
>
> So except for the times I am using the dynamotors, I run the receivers 
> in the test jig and out of the racks at about 175VDC, transmitters at 
> about 540VDC. (By the way, even 175VDC is enough to blow the .05's, so 
> I am on a long term quest to replace all, either with re-stuffed cans 
> or just wiring them in. Otherwise, letting them fail is like playing 
> condenser Whack-a-Mole)
>
> My question is about the receivers... aside from maybe the 12A6, are 
> there any downsides to lower overall plate voltage?
>
> Thanks
>
> Ken
> W2EWL
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