There were three versions:-
Telephone No. 92 Mk 234
Fitted with Transmitter No. 2 and Bell receiver.
Telephone No. 92 Mk 235
Fitted with Transmitter No. 3 and Watch receiver (see picture).
Telephone No. 92A
As per the Mk 235 except the circuit is modified to allow the telephone to be
used on CB exchanges.
Circuit diagram - Web
users click here - CD users click here
Pictures were taken in 1915.