There is an excellent forum for vintage radio collectors and restorers called UK Vintage Radio Repair and Restoration which can be found on  http://www.vintage-radio.net/forum/ . I have no doubt many of you are subscribers to this forum. Recently, someone called “Carnival Pete “ (subscribers tend to use pseudonyms) raised the question as to why the Eddystone 888A Amateur Band receiver would have P.U. audio input. Subsequent discussion showed that this was a common feature amongst many of the Eddystone communications receivers viz; S.670, the 730/4 and the S.680/2A to name but a few. The collective consensus was that this was to enable the set to monitor sidetone transmissions from an co-located transmitter when in standby but that it could also be used in connection with a gramophone perhaps more aimed at the ex-pat market overseas. Also some Eddystone features just seem to be a standard. Perhaps because designs evolved from one to another. Interesting discussion.