Tested on 24 volts and it works nicely, it could use up to @ 28 volts.
I used 2ea 12vdc 1a supplies in series.
It takes a while for the case to really warm up.
No annoying humm.
Simple but neat-to-hear vacuum tube sounding guidance radio.
It works with a small 8 ohm speaker or most headphones
with an adapter, or connect wires on to it directly inside.
Extensive specs, info, details, and it's history is easy to find online.
Not that much is heard on the variable frequency ranges it tunes in.
Maybe some guys in Europe were experimenting
with the 200 to 400 khz range but that's too far away to hear.
This is a lf and mf radio, it only listens, it's legal and has no transmit.
It might be useful to detect radio noise interference
that you might be having & hearing at home,
like an am radio would find.
Maybe you guys know of another cool use for it.
Someone has probably already made one into a mini guitar amp.
This is a neat old, almost square cube black box,
a collectors item in pretty good shape, reliable, rare & a low price.
No photos of this exact one here, it's a common beacon radio,
a Signal Corps, 2 knobs, with 5 or 6 total connections,
6 if you want to "ground" your antenna system, like you should, and
if you put a wire antenna outside, per instructions that
you can easily find. And there is also another shock hazard,
a danger warning for you if you are getting inside this radio.
It can use most any simple antenna, window/metal structure/piece
or a short "long wire" for an antenna 2 feet long,
and "hears" these AM modulated frequencies from miles away.
These frequencies are usually not heard, or common
on most short wave radios, but there is stuff to hear,
stuff no one else hears or listens to; industry data pulse/tones,
some other odd tones - mysteries, maybe harmonics,
machine noises, static, your smart meter's buzzes, distant
lightning crashes, but not much else. So it's in a different kind
of a peaceful, forlorned radio zone, no adds & no talk, maybe,
with "it's own, unique set of cool vibes" that you can pick up.
Questions?
The first $50 gets it. Send your phone number.