[Arran]

Most of us buy 630 VDC rated film caps, those seem to be the most readily available, and will work in most applications. The vibrator cap is a hash capacitor and it does have a higher voltage rating, usually above 1 KV, sometimes a radio will have a 1 KV cap across the output transformer primary for tone correction though not always, I think you can use two 630 VDC caps in series in either application, but not sure about the hash capacitors. I have a Stewart Warner that is a 6.3 volt set that has a synchronous vibrator, hopefully I can get it working as it uses 2 volt battery tubes, so it would actually be practical to run it off of a 6.3 volt SLA battery as a "cordless tube radio". I also have a pre war Philco car radio, 1939 vintage, but I think it's beyond repair as the set sat in water at one point.
Regards
Arran