When I purchased my KPA500 at the end of last year, I didn’t have a 240V outlet in the ham shack, so I was forced to run off of a 120V feed. Unfortunately, the ham shack is about 75 feet away from the breaker box, so there was some pretty hefty IR drop on that circuit since the amplifier pulls about 10 amps. As a consequence I would see the HV drop from 76 volts in standby to 55 volts at 500 watts output.
In general I didn’t use the KPA500 often, and I rarely use SSB. But a HV reading below 60 volts was disconcerting because it can lead to increased IMD.
I finally got around to running a dedicated 20A 240V circuit to the shack this past weekend. I’m happy to report that the minimum HV under full output is now 64 volts — an improvement of 9 volts due to reduced IR drop on the power feed. As a side benefit, I noted that it requires about 2 watts less drive to produce 500 watts of output.
