WWII AMPLIFIER, AM-115/APX-15A, for AN/APG-15 Radar Set , Display or Parts

Description

For sale is a vintage piece of equipment that my late father brought home after WWII.   He was an Army Signal Corps Radio School instructor during the War, and after the War he purchased several pieces of surplus radio equipment.   I'm sure he had great intentions of either using parts or just "playing with it" to see how it worked.   However, I found it pretty much as he brought it home.
The tubes are missing, but the sockets are identified.   You will have to look at the photos to see exactly what is included.   We slid the cabinet off to see what was inside, and everything looks clean.   (see photos)
I had no idea what this unit actually was, but a super-helpful collector from the "B-29 Corner" (Amazing website!  Check it out!) helped to describe for us what this piece is:
It is part of a small batch of low frequency amplifiers that were produced as an attachment for AN/APG-15 gun control airborne radar sets.  It was made feasible by the discovery that the U.S. aircraft radar could detect the rotation modulation frequency of aircraft propellers caught in their beam.  Further studies produced the fact that all known Japanese fighter planes produced a propeller modulation frequency above 70Hz, while those of a B-29 were between 40 and 63Hz.  This provided a unique opportunity to detect whether a flight of aircraft were friend or foe - sort of a low tech IFF without needing a transponder.  That's what the APX-15 was intended to accomplish.  I don't believe it was widely fielded.
CQE was Bell Sound Systems in Columbus OH
Thanks, Mike!!
(I have 3 of these left.   The black paint on these is starting to scrape off a little on the corners, but the units are still good.   I know the shipping is expensive, but I just shipped 2 together, and the added shipping for the extra one was very minimal.   It may depend on where you are located, but if you're interested in buying more than one, email me for a shipping cost before you buy, and I'll figure the shipping for you, based on your zip code.)
I hope that this is a piece of WWII equipment that you would love to show off in YOUR collection!!
Thanks for looking here!!
(Radio shelves)