That will, very likely, be an Armstrong-circuit regenerative radio based on a common tube of the day, and what comes immediately to mind is the O1A, a 4-pin triode and good performer.

Filament voltage is 5 VDC - polarity not critical.
B+ will be 90 - 135 VDC
Grid voltage will be -4.5 - -9 VDC

http://www.bunkerofdoom.com/tubes/sy...A/1943/P20.GIF

Overall, those early triodes were not very efficient as compared to "modern" miniatures of the late 1940s and 1950s.

Note that this basic design often included a variety of plug-in coils for conventional broadcast, SW and other bands as may have been available at the time. Keep in mind that 'official' regulation of land-based broadcast radio did not start (have teeth) in the US until ~1927. And, pretty much every Tom, Dick, Harry, church, department store and other organization had its own radio station, not to mention thousands of amateurs. So, the concept of staying with any given 'band' was not regulated.

Peter Wieck
Melrose Park, PA