Do you have a variac or similar which would allow the mains volts to be raised slowly? I have a TS-530 and I recall that the 400V HT (and doubler) is present even when the Rx is on.
There is a very active "kenwood-hybrid" group at
https://groups.io/, the 830 is probably the main topic of conversation. There are a few "known issues" which arise as they age, but mostly those which you'd expect and easily dealt with.
B