mynick wrote:

no shorts between magnetron contacts or ground but when plugged it
does not heat the oven contents and has loud hum
Is it dead(how to make sure) or perhaps requires say 1v higher cathode
heating voltage than what transformer supplies?
Sounds like it maybe the HV-Diode..

P.S.
You most likely won't be able to test it with your
DMM unless it's totally shorted.