Military Radio Headset/Mic Test Harness

©Brooke Clarke, N6GCE

stock 5 pin
6 pin & Switch Mod


General Information

This is a very handy device if you work with U-229 type audio accessories.  Instead of trying to hold test meter probes on top of the U-229 connector pins, you can just calmp them using the U106U Silver spring clips.  There are 5 wires in this unit, so it is not good if you are working with the newer 6 pin connectors.  The Ground U106U has a balck rubber boot installed so that it is easy to find.  The terminals are marked:


Many of the modern military radios use the 6 pin AUDIO connectors that take the U-329/U plug.  By replacing the U-229/U 5 pin plug and using a cable with more conductors (Alpha Wire AE p/n 1176C, 6 cond, #22) and replacing the scoket this audio test adapter can be used for work with 6 pin AUDIO accessories.  To make it more useful an on-off-(on) switch was added from the C "PTT" pin to ground.  The "(on)" position is momentary and in the "on" position the radio is continously keyed, a handy feature that saves one hand.

The added "F" terminal is used by the PRC-68B, -126, -128 and -136 for the channel frequency assignment digital data up and down loads.    It turns out the the PRC-6725 & PRC-139 use pin "E" for digital data and they do not have a provision for external DC power on pin "E" like the Magnavox squad radios.

This modification is really handy when working with the various fill and data modes of the U-229 family of equipment.

The top is marked G.R.M Corp, 13567.  A DLIS CAGE lookup on that number returns ITT Night Vision?.
Telegenix Inc. (formerly knows as Grim or G.R.M. Corp) -

Top View - there is a black rubbr cap on the A ground terminal
Side image showing three of the U106U spring clips.

These can be found at American-MilSpec and occasionally on eBay

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