Clansman intercom wiring

[philm1]

Are there any wiring experts out there who know how the wiring from the connecting cord goes to clansman headsets and mic?  What colors do what?

I have some American helmets that I am hoping I can replace the cable on to a clansman cable.  There seems to be a similar number of wires of similar colors. 

The American helmets are probably set up for PRC.  Photo below is the box that goes on the side of the American helmet.

 

 

[Mk3iain]

Would be interesting to see how you get on here, though I am not sure they would be compatible. I hope they are, but there are for example different types of mic such as electret. I used to have a better idea on this stuff working on US and European aircraft but its a distant memory now..

Good luck with it !

[andym]

Google is your friend for this, there's lots of information on the 'net about modifying Clansman headsets for various things.   Here's the headset pinout: http://www.g0ozs.org/clansman/audio.shtml

Andy

[g0ozs]

Ideally you should get EMER C472 from VMARS or another archive which is the Clansman Headgear technical description that includes circuits. In summary the transducers in the original 1970s series of headsets and handsets are all 300 ohm impedance and of dynamic (magnetic) type, the PTT is a 2 pole switch both connecting the microphone to pin A when pressed and connecting Pin F to ground/ The two earphones are independent each being connected between pin D and ground or pin F and ground. Handsets with one earphone and speakers are driven from pin D (left ear).

Colour coding is not quite standard between headsets - the commonly available Pressil Switch replacement cables terminated with a 7 pin plug are:

PIN     COLOUR

A        RED               MIC

B        GREEN         MIC

C        No Connection  (Is power from radio if you need to operate an electret) 

D        ORANGE      AUDIO OUT (Left Ear)

E        White (connected to screen of cable)  GROUND

F        Black PTT 

G       BLUE    AUDIO OUT (Right Ear) 

The later ANR headsets did need power so pin C was connected through. 

[Mk3iain]

Would this work for wiring US helmets to a Clansman headset cable ?

Are US standard microphones and speakers the same as Clansman, or compatable?

 

Edited August 30, 2020 by Mk3iain
The usual.

[g0ozs]

Iain

Most of what I know about US handsets is from Brooke Clarke's site http://www.prc68.com/I/H33.shtml and his other pages. The H33 (12 pin connector) and its relatives seem  to have a carbon microphone (which needs a DC supply to work) and a lower impedance earphone - having said that German versions of H33 for the SEM-25 and SEM-35 radios which are mostly what turn up in European surplus stores and ebay auctions do have a higher impedance dynamic microphone - I know because one did not work as the operator headset of a SB-22 telephone exchange !

The more recent ones with 5 pin connectors for PRC-25, PRC-77 and later sets are covered by http://www.prc68.com/I/U229AA.shtml http://www.prc68.com/I/H250.shtml and http://www.prc68.com/I/Images/H161ASch.jpg - These seem to present 500 to 1000 ohms to the audio output of a radio as a headset and about 150 ohms as a microphone so are probably within the compatible range. 

The Clansman loudspeakers are 60 ohms so any higher impedance should be OK. 

The microphone impedance should not be critical - what matters is that the microphone does not need DC power if it will work with an unmodified lead (the set does provide power on pin C at 18-24V depending on the type, limited to a few mA, so will power a modern electret microphone, but this is not connected to normal headgear. It is less likely that the set could power a vintage carbon one for which a separate battery and transformer coupling as in a field telephone is a better plan. Microphone audio levels need to be in the range of 20 to 40mV peak into the radio if I remember rightly but the sets have audio automatic gain control and are not at all fussy. 

HTH

Iain

73 de G0OZS

 

 

[Mk3iain]

Thanks Iain !

Phil, That should be enough to work it all out but what exactly do you have ?   Are they sourced from the US or supplied with US armour used in Australia or New Zealand ?

Iain

[philm1]

Thanks guys.  I did try google plus some local electronic experts but no one could really help. In the end with some perseverance I have managed to get things to work.

What I had was American crewman helmets that I wanted to re wire to clansman to use in our CVRT.  

 

there is an elaborate box on the helmet side where the press to talk is and the cable splits to 2 plug outlets

 

 

All I really had to go on was this diagram and a replacement clansman cable. By checking continuity between pins in the connector and the colour wire at the other end I could establish what colours were what pins.

I then sat down with the helmet to establish what did what.  First I used a small battery across each ear piece and the mic and if they crackled I knew they probably worked.  Then in the PTT box I traced where wires went and what they did.  Sounds easy but it did take some time as the PTT works by pushing it both up and down.

Next step was to buy some wire of each colour to wire into the PTT box which I could then connect the clansman replacement cable.  I did this as the only way to test functionality was to plug it into the live intercom system and it was easier to change wires around externally then to keep fiddling in the PTT box.  I left the clansman PTT cable switched to open mic and eventually got the helmet including it's PTT to work.  I no way say this is the correct way but it did work.

Here's the replacement wiring set up.  The only modifications were to shape the screw in plug to fit the PTT and put a wire across the black and green.  Don't know why but it made it work.

 

 

There were several helmets to do so more cables were ordered.  The cables I got were not all the same so I recommend you only get the ones with the small rounded metal ends as they are easier to work with.  I opened out the ends,  drilled a hole, filed down to fit. 

The cables with the plastic ends I learnt not to cut as the wire is very fine and hard to solder.  You can pull the pins out of the connector which I then soldered to other wires to connect to the PTT.   

Best of luck.  i now have 5 helmets good to go.