Bruce.
I was reviewing this thread again and a couple of things struck me in Post #1.
Firstly...don't Gunners speak rather loudly anyway?
Second. The photo of the loudspeaker with all it's original markings caught my attention, as one of mine is identical.
I have heard many people over the years say quite emphatically these loudspeakers were never used as an audio output for the No. 19 Wireless Set, they were strictly part of an artillery battery communications system. But the original markings on these loudspeakers clearly shows two distinct options for land line connection. The upper terminals would appear to be intended for the artillery tannoy system, and the lower terminals for connection to a 19-Set.
But how is the 19-Set connection accomplished? There are no direct land line terminals on the 19-Set. There must be some sort of interface component required to tie the two pieces together. I thought perhaps the near side Wireless Remote Control Unit might be the answer, but no mention is made at all in the manual for this remote control, for that type of usage.
I think there is a Control Unit in the Wireless Set No. 19 kit options that was designed with land line terminals, but cannot recall the reference number for it, or if the loudspeaker was its intended purpose. One would think instructions would have been printed somewhere covering this form of loudspeaker usage.
An interesting mystery. Thanks for posting.
David