I knocked up a 1kV PSU to test some 813's I had, video here -
https://www.youtube.com/watch?v=XybEOt6XzXI . I got six good valves out of 7, not bad, as I bought them untested.
One thing I was concerned about is the DC blocking capability of the bridge rectifiers I used and diodes in general. The bridges were GBPC2508's at the high voltage end with jerry rigged bridges made out of 1N4007's at the lower voltage end ( tfmr secs in series, stacked as in attached. As you see he uses 1000V bridges here). The datasheet for the 08's says 800V PIV and DC blocking. I measured 20V ish DC on the winding that fed the "top" bridge, whether this was actual DC or a misreading by my DMM I'm not sure.
If it is DC leakage I'm reading, would putting an EHT diode in series after the bridge and smoothing cap be beneficial? I intend to build a 2500V PSU eventually, this baby HV PSU was by way of a test.
Andy.