Hi Tom,
Questions about the Philco FM1000 tube have come up before. I know of no appropriate sub for this tube, but FM1000 tubes are available from several tube dealers and are not overly expensive. I posted an answer to a similar question for information regarding the Philco FM1000 in another radio forum earlier this summer. Rather than repeat it here, you can view it at:
http://antiqueradios.com/forums/Forum11/HTML/001317.html
Poston
:Repairing 1948 Philco which has a ratio detector tube numbered FM 1000. Does anyone know a sub for this OR
:Hickok 600A settings? I have an very extensive library and do not find a reference. Thanks, Tom