1948 A.R.C. Tom Thumb Portable Radio

[Electronic M]

I have a Motorola radio that used that voltage of battery...I just used the closest multiple of 9V (seven batteries in series). The radio didn't care that it's B+ was about 5V low.

If you can identify cathode(filament in this case), grid(s) and plate leads on the riders and you know the tube is a 3S4 (or some other number) just Google the tube number plus the word datasheet the datasheet will tell you which pin numbers correspond to which elements of the tube. I've done that to figure out blurry/vague riders before.