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Need help splicing u-94/u ptt with u-174/u military plug.


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New user. I'm not an electrian or an avionics tech. I'm trying to splice together a u-94/u M9177/5-2 tjs-102 ptt switch with u-174/u M9177/2-1 tp-101 military plug. Actually a simpler statement would be that I'm trying to install a 174 plug onto a u-94 ptt switch. For use with a military headset. All military; I'm not trying to convert anything to civilian. This is all surplus Army aviation gear that I'm setting up for ground use with military portable radios that accept 174 plugs.

I have a surplus issue David Clark (H10-76 I think) headset plugged into the ptt. For testing I have a two wire external speaker, a battery power source, and a simple light bulb current tester. Started with 9 volt battery and switched to a 12 volt car battery. With either of these batteries my test gear squawks and lights up but I think army helicopters run on 24 volts with some systems on AC and some on DC; I don't know if that matters. I have tried various combinations and I can produce squelch in the headset and external speaker as well combos that verify the ptt breaks squelch but I'm not sure if any given wiring combo is correct. I have not been able to produce any sound through the microphone; if that is even possible with test set-up I have. I don't know if I need AC or DC. I'm obviously lost and have no clue.

Can anyone provide a simple color to color wiring solution? I'm out of google search ideas. The ptt leads are all one wire per color; red, black, green, white, and the yellow jumper for the ptt switch. The 174 plug leads are: 2x White, 2x Black, 1 red, and 1 green. If someone could just tell me which wires go to which wires that would be amazing. 

Edited by Dale
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From your post, I assume you’re trying to replace the u-94 jack with a u-174 plug or trying to make an adapter cable with a u-174 at each end so as not, destroy the u-94 jack.

With the documentation at the link below, you should be able the back-track the wiring. Open up the u-94 jack and plug in the u-174 plug. From there, you can back-track the known wiring form the u-174 back to the correct connections on the u-94 side. You can also see how the David Clark H10-76 u-174-plug wiring matches up with the u-94.

It’s not as hard as it may seem, the system effectively (on the headset end) only uses four (4) wires, two (2) wires to the mic, two (2) wires for the speaker or earpiece. The only reason you have six (6), is they parallel-off two additional wires from the base pair of speaker wires to a second speaker or earpiece. There may be a seventh wire, often used as a shield ground.

Upstream of the u-94, you normally have six (6) wires. Again, two wires for the speaker/earpieces and two for the mic. The remaining two wires for the Press-To-Talk (PTT). 

PTT wires are often blue/yellow, mic- red/white, speaker-white/black or white/green. The normally always wires are, red-mic and white or black speaker.     

Color codes may differ between manufacturers, so don't expect a color-color solution. However, plug and terminal designations are constant.

See link: Wiring Document U94/U174

Your u-94 is probably pretty close to one of these  below:

u-94 color/function
Red- Microphone High
White- Microphone Low  
 Speaker High 
Black- Speaker Low
Yellow - PTT High  
Blue- PTT Low 


Edited by iChris
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Thanks for the reply Chris. Sorry for delayed response, wasn't near a computer. Yes, this is essentially going to be a short version of the long comm cord used by helo crew chiefs when they dismount from the aircraft. In this case I'm using aviation and/or similar compatible headsets plugged into a handheld radio (think MBITR) and I need a PTT switch. In this case, I'm attaching the cord and 174 plug from a pilot's helmet to the U-94 PTT because the pilot's cord is thinner, cloth and flexible. Easier to wrangle around all the crap molled onto my body armor. It will be a few days till I can plug into a SINGARS, MBITR, or helicopter; and of course that's when I'll need this thing to work. (yes, I'll have the different QD adaptors when I get there.)

I had found most of the schematics you gave me links for but with no real electrician skills to speak of I was just swimming. I do appreciate the links though, putting them together helped me figure a couple other details out. But I found a lot of other schematics that seemed to contradict each other, like these two (don't remember where I saw it but it was opposite the one on the left.):


The mechanics I can handle. I can make very solid splice connections using pin sleeve connectors and I can solder. I can make a splice as strong and durable as an electrician. I just need to be sure the invisible juice is flowing proper.    

I had tried through experimentation to use batteries for power source but all I could be sure of is that I had static in the phones and I could hear the PTT break squelch. So yesterday I disassembled an old handheld and attached leads from the plug pins to the two wire speaker. It worked, I could send to, and receive from another radio. But in order to transmit I had to use the PTT on the handheld. It didn't matter whether I used the headset's U-94 PTT or not, when I keyed the handheld it transmitted. So I was sure everything worked but couldn't be certain about the U-94 PTT.



So, I had figured out (duh) that the extra white and black leads on the pilot's plug are for the seperate speakers that would have been in the helmet; and for what I'm doing they're redundant. (As you said also) And I'm assuming the plug on the David Clark headset has only one lead per tab because the "Y" junction for the seperate speaker is farther up the line in the first speaker housing. Still stumped why the plug pin locations seem different than the pilot's plug, but to hell with it, it works. The pin locations on the plug and PTT match so I'm just going color to color on those leads. So, the only thing left is where do I stick that yellow bugger? I'm assuming it should be spliced with the white leads from each cord.



David Clark Headset schematic:


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On 4/22/2020 at 3:20 AM, Dale said:



Your speakers are not polarity sensitive so bands 2 & 4 (speaker wires) on the u174 may be reversed wired without a problem. The same for the mic bands 1 & 3 (mic). In most cases the mic is not polarity sensitive. However, with an older mic or special purpose designs, you may have to swap the mic wires around. Once you identify your mic wires, any reverse polarity won’t hurt the mic, it  just won’t work,  just swap it. 

 Your PTT switch above is yellow/black wiring between your radio and the u94. It could be one or two wires. The one wire setup eliminates the extra wire run by using the shield ground at the u94, see photo below. What you have is a momentarily "on" switch that grounds the radio's PTT circuit to key the mic.

If you’re going to eliminate the switch, you don’t need the yellow wire. If not, the yellow wire should go to one of  the two terminals on the switch and the other switch terminal should have a connection to the black (GND) wire. 

 On one of  the four terminals on the u94 receptacle, you may find a black and white wire soldered to the same terminal. There’re using the black (GND) wire as the speaker return wire

  Isolate-Detect- Correct, the old troubleshooting adage.





Edited by iChris
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