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