[Milsurplus] myster box

[Ray Fantini]

The more I look at this thing the stranger it gets, couple weekends ago
while attending a small hamfest over in New Jersey I saw a table with
assorted WW2 items on it, the usual ARC-5 stuff and the like. Their was
a receiver about the size of a shoe box that had a ARB remote tuning
head with right angel adapter on it and looking at it I thought that
maybe I can sell the head on EBay so I paid $5 for it. After removing
the head I started looking at the receiver, the more I look at the
receiver the more I realize I have not seen anything like it before.
There are no identifying plates or markings on the radio, it has a
primitive coaxial cavity input directly coupled to a 955 mixer that is
fed by a 955 oscillator tube located next to it. The oscillator tube is
tuned by a movable signal plate capacitor that travels in a cylinder
located on the front of the radio, this is wear the ARB head was
connected to vary the capacitor. The size of the tuning plate is about
as big as a half dollar. The output of the mixer ( 955) feeds the first
IF transformer and a IF string of 6AC7 tubes, beyond the third IF stage
is a 6J5 oscillator capacitor coupled to the grid of the fourth IF amp,
don't appear to be a mixer, just like a injection for no reason I can
determine. Then there are three more stages of IF amplifiers all 6AC7
and a 6H6 configured as a envelope detector. The output of the detector
is capacitor coupled to a 6AC7 then a 6AG7 and carried out to a coaxial
connector. It appears to me that everything from the detector out is a
wide band video circuit. Also there is no AVC/AGC system, the only thing
that may be controlling gain is that each IF stage has a strange
arraignment wear the cathode of the amplifier is fed to the suppresser
grid by a 150 ohm resistor wear it has a bypass cap to ground and then a
100 ohm resistor to ground, maybe this is some strange gain control
system? Will eventually get around to connecting a plate and filament
supply to this and then determine operating frequency and IF bandwidth.
Looking at the frequency control would feel this thing has to be
unstable but who knows? My ideas of what this is go from a primitive IFF
receiver, the old systems just transmitted continually and maybe this
was the ground receiver to feed into some type of decoder? Or maybe
it's a television receiver for some type of onboard imagining
system but with no AGC can't see that working?  It's a very strange
box.
Ray Fantini KA3EKH