Made by Standard Electrica S.A. Madrid (ITT). Feature-wise a standard field telephone, magneto, ringer, battery compartment, pluggable handset with P.T.T. button mounted to a metallic body-frame put into a wooden box. Design, setup and features are similar to a German FF 33. But what makes this device very interesting is it's interior construction. There are no wired connections, all the electrical connections are cast into a top and an additional vertical bakelite panel to where the components are mounted directly. A type of early circuit board implementation unknown to me to have been used in any other field telephone.
Most sources mention that this instrument has been developed in the 30ies and used in the Spanish civil war (1936 - 1939).
The handset type (BTMC 2290-A based, developed by BTMC in the early 30ies) and the use of a wooden outer box could point to a 1930ies development.
Also the anti-sidetone circuit setup is possible, by the mid 30ies a lot of field telephones already used anti-sidetone setups.
But the few models where I have seen photos of the innards all sport capacitors from the 1950ies (mine from 1957) and a plastic handset cable.
Also the type of construction with all connections embedded in bakelite panels seems to me to be a concept too modern for the 30ies.
The only other telephone I know of built around a somewhat similar concept is the Kellog Masterphone 1000 which was developed in the late 40ies by then still Kellog.
By the early 50ies Kellog was taken over by ITT, the same which is also the parent company of Standard Electrica S.A.
Perhaps the Kellog Masterphone 1000 design was the inspiration for this bakelite circuit board design?
If anybody knows more any feedback appreciated!.
Update June 2021: A Spanish field telephone collector/specialist informed me that the exact year is unknown but that the device was introduced after WWII, perhaps as early as 1945, and that it was in use by the Spanish army up to the mid-1980ies! (Gracias Cesar!)
Ready to use.
The diagram (mounted inside the wooden box top lid).
The electrical circuit is pretty standard, using an anti sidetone coil setup.
Completely disasembled.
Disassembled handset.
The handset is of the typical BTMC/ITT design (Type 2290-A) used on BTMC/ITT instruments in many countries from the 30ies to the 60ies.
Neatly lined up components.
The two capacitors hinting to a mfg. date of late 1957.
Ringer.
Magneto.
The top board from below.
The coil is mounted directly to the top board.
The four pins to the right of the coil connect to the vertical board.
To the right of that the pin of the test button.
The top socket is for the laryngophone, the bottom sockets are line sockets.
The central board, magneto side.
Three connectors for the magneto circuit.
The central board, ringer side.
2x two connectors for the capacitors (on the left = top).
Two connectors for the ringer (on the right = bottom).
The contacts are for the test button (activated when button pin pushes from top to the contact).
Components mounted, top still off.
Assembled body (still without battery cup).
Components connected to the central board.
Completely assembled body, lids still open.
Completely assembled body, lids closed.
Before putting in box.
5-Pin Handset connector.
All stored.
Ready for transport.
Accessories i got from EZESAR: Leather carrying strap, 3V battery, laryngophone (throat micro), headset, original textile handset cord.
Detail of strap hook.
Original 3V battery mounted.
3V battery type PS-6003, made specifically for the Spanish signal corps.
Laryngophone and headset connected.
Headset detail.
Laryngophone detail.
Handset with original textile cord.
C-30301 training unit (from private collection, EZESAR, Spain).
Capacitors are from 49.
C-30301 training unit, model with different magneto (from private collection, EZESAR, Spain).
Capacitors are from 63.
Magneto detail.
Creative Commons Attribution-ShareAlike 4.0 International License