I found this neat old telegraph sounder on eBay back in 2008. It appears to be British, and it is marked:
SOUNDER RELAYING TYPE B
I do not know much about it, other than it is clearly designed to provide both audible feedback and electrical switching. In other words, it’s a deliberately noisy relay which can both repeat an incoming telegraph signal and allow an operator to copy code by ear. It has a wooden base which appears to be intended for mounting on a wall, and it’s covered by a wooden lid with a glass window.
I’m interested in learning more about it. How old is it likely to be? Was it military, civilian, or dual-use? Please email me or comment below if you are familiar with this type of equipment.
I have been clued in to this page on which I found:
Type B was used for remote control of high power W/T (Morse) transmitters, including transmitters T.70 and T.1087. The morse code operator could be many miles away from the transmitting site, and this instrument, connected to the site by telegraph wires, faithfully followed his/her Morse keying to operate the transmitter. […] Type B (Ref. 5B/138, later designated 10G/138). Power supply: 14v ac through a bridge rectifier. Coils 500+500 ohms in series, slugged with closed metal rings round the coils. Used for keying a transmitter by remote control. According to the RAF Museum, Hendon, Type B (10G/138) was a stock item in RAF Stores until "some time after 1959".
— Tony Smith G4FAI via morsemad.com