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Old 08-07-22, 02:37
Chris Suslowicz Chris Suslowicz is offline
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Join Date: May 2007
Location: England
Posts: 814
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Hi Dan,

1) Driver + Bow Gunner are connecting to Junction Distribution No.1 or No.3 box with the "Call Commander" push button on it. This is intercom only, and which one is fitted depends on the number of slip-rings available in the rotary base junction to the turret. No.1 is the early type and just has Speech & Signal available, so gets +12V and Ground from the vehicle electrics and requires the "Tannoy" power microphone version of the headset (the grey lollypop). Later vehicles had more slip-rings available and used J.D.3 which fed Mic+ and Mic- through the junction and allowed the standard (black bakelite) Microphone and Headgear to be used.

2) The Gunner is actually the Wireless Operator/Gunner and has Control Unit No.2 with a red light on it and two switches: set selector (A, IC, B) and rebroadcast (Normal / Rebroadcast). The red light indicates "A set unattended" and will come on if none of the headsets are switched to the 'A' set. The 12-pin connectors are a pass-through, one will go to the WS19 and the other will go to the commander's control unit (No.1 or 1A, probably.)
Cable from radio usually goes into the connector on the side of CU2 and the cable between CU2 and CU 1 (or 1A) into the top one on each box (I think).

3) Early cables (brown paxolin inserts) were supplied in sets for specific installations and were crimped and/or soldered in the required connector orientation. This proved to be a big mistake (from a production/logistics point of view) and later cables (black bakelite inserts) could be changed in the field when the radio was being installed. If you have the later cables and remove the spring clip around the cable entry, the back cover can be lifted, unlocking the rear part of the shell. You can then (carefully, as the cable may be fragile after 80 years) rotate the rear portion to the desired position, lock it in place with the back cover, and re-fit the spring clip.

4) Is the Driver/Bow Gunner box a Junction Distribution No.1 or a No.3?

5) is the Commander/Loader box in the turret a Control Unit No.1 (or 1A) or a Junction Distribution No.1 or No.3? I think it should be a C.U.1 (or 1A).

6) a - maybe. It depends on the number of slip-rings in the rotary base junction. Early AFVs required the use of J.D.1 and 2 because there were only 2 spare circuits, later ones used J.D.3 and 4 with standard headsets. The early type had a 6-way cable from the WS19 Supply Unit to the turret junction box to allow for 2 x 12V feeds (split 24 volt vehicle power), SPEECH and SIGNAL. The later version used a cable from Control Unit No.1 to get the SPEECH, SIGNAL, Mic+ and Mic- into the lower hull (and used the IC Amplifier and standard headsets instead of +12V and Power Microphones).
The M4 Sherman wiring diagram shows both options (I think), which is confusing to the unwary.

b - later cables can be re-polarised to suit the intended application.

c - Argh! It's 01:37 and I have work tomorrow...

Good Morning!

Chris.
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