Hi,
This is a 6 AIRCRAFT headset microphone amplifier system made for an aircraft. The "no heat" label at the top of the mic amplifier means that this unit can be used in any weather, and at almost any altitude, without requiring a heater unit in the aircraft to function properly. That is what gives this away as an aircraft comms system.
It is a B&K Precision instruments model SQ-305-1, serial number 102. NOT Bruel & Kjaer, LOL.
The microphone connectors are for TWO WAY headsets, common in military and older
civilian aircaft. These have fallen out of use in civilian aircraft, but not in military ones.
The plaque of Pratt & Whitney is probably NOT originally a part of this unit, however, it may have been used as part of an overall Pratt & Whitney retrofit of a large aircraft. Although Pratt & Whitney is known for of all things rocket engines and WWII propeller engines for our famed Mustang P51 fighter aircraft, they also almost always do custom stuff, mostly for military and large civilian air contracts. If they get a contract to service a fleet, they do all the maintenance, retrofits, etc. Gotta stay competitive.
The stickers "29" and "30" above the microphone connectors are meaningless, and on the front panels of each amplifier unit, ignore them. Someone put them on there long after this unit left the aircraft or even the control tower it came from. Being as it is a multi channel unit, that is also a possibility.
The AC three prong center offset connector looks like it is from the 1950s or 1960s, so this unit is definitely old.
I would start by emailing these kinds of places for some understanding as to the wiring of the mic connectors, as they are pretty standard:
http://aircraftprecisioninstruments.com/
And other places like aircraft restoration forums and old aircraft fan sites, even maybe some HAM radio forums, they should have more details on this model.
Lastly, the company might still exist, although I seriously doubt they have the schematics, but you are welcome to try them out:
http://www.bkprecision.com/about-us.html
Here are a few links to aircraft stuff to get you going:
http://aircraftproducts.wicksaircraft.c ... -intercoms
http://www.skygeek.com/aviation-communications.html
And what a new plug looks like, not a bad price either:
http://www.ebay.com/itm/Metal-Flange-25 ... 1132303758
A possible pin out (TELEX standard mic with two earpiece):
http://www.watamix.com/rtspinouts/#US14
Another possible pinout, Sennheiser (based on the standard type):
http://plsystem.com/pinout3.htm
Look for model HMD-26-X
CHEERS.
Howling at the neighbors. Hoping they have more mic cables.