I agree with gadget73. I'd take the back off the radio and have a good look at the transformer; as he said, it may have simply overheated. If it's gone, I don't know what to tell you, as I have no experience with this particular Zenith (although I do have three wood-cased Zenith table models, all from the '60s and all with series-string filaments, although my '65 MJ-1035 has an unusual series-parallel filament arrangement [two strings], with a 6.3-volt transformer feeding both of them).
If the original transformer smells as if it has been burning, there may be other problems, such as a shorted rectifier tube (some of the early Zenith radios had real problems with their 6X5 rectifier tubes shorting and taking the power transformer with them). Any time a transformer gets so hot it smokes and/or burns, you can be
sure there is a very severe overload somewhere. I don't know why Zenith didn't design these older sets with fuses in the power supply; as much as they must have cost when they were new, I'm sure a fuse wouldn't have added
that much to the price.
If you have to replace the transformer, you'll need the Sams Photofact on the radio so you can determine what type of transformer to get. It would have to be either a Zenith transformer from a junked set or a generic transformer that can supply the required voltages, although in this day and age of solid-state everything that runs on 24 volts or less, high- or multiple-voltage transformers are becoming
very difficult to find.
Good luck. I hope you get that 8H832 singing again, as those radios, like all Zeniths from the '40s through the '60s, were excellent sets. I like my three wood-cased sets, although the MJ-1035 has issues with the volume control and doesn't work very well at the moment. However, the other two, my K731 and C845 (my avatar is a picture of a C845 very similar to mine), are working just great and sound excellent, which was a hallmark of Zenith radios from the '40s through the '60s (that's why I like them so well; that and those fine wood cabinets).
Your set probably will sound just as good once you replace the transformer and the filter capacitors (a short in one may well have been why the transformer burned).The 42-50 MHz FM band, however, is no longer used for FM broadcasting; it was, however, the original prewar FM broadcast band, before the present-day 88-108 MHz band was commissioned. Those frequencies (42-50 MHz) were originally used as television channel 1 (circa 1946-49), then when that channel was abolished in 1950 or so, the same frequencies were realigned and eventually became the amateur radio six-meter band.