Before I forget I'm using opto couplers for plate voltage and current to the VTVM 'cause I use a plus minus supply that needs a floating ground. So plus minus 1500vdc for the plate supply on a floating ground for the plate circuit, and 500vdc plus minus at an earth/input/output ground for the screen and control grid, with the screen at earth/input/output ground so I can run control grid swapped to input ground for drive from the transmitter.