To add my two-penn'orth; my Prentice, when I bought it for £700 st Sywell in 1967, came with the original RAF 4-channel valve VHF, together with what I assumed was an original RAF throat mic. I borrowed an fabric hat with integral earphones liberated by a RAF friend. I suppose there must have been 2 jack sockets, mic and earphones, for each seat somewhere, but I have no recollection where. The throat mic worked OK, but after two or thee hours it got very uncomfortable, because it had to be tight to work.