New: find more details on U.S. fieldphone history on the U.S. Signal Corps Field Telephones Timeline.
The US EE-108 is a sound powered field instrument developed in the late 30ies and used in WW2 and later. It's basic design is based on the local battery instrument EE-8. The leather case, generator, ringer and capacitor are interchangeable with the EE-8. The instrument can be used on point to point connections with other sound powered or local battery instruments, or also connected to a local battery switchboard.
The US instruments TP-3-T1 and TP-3 are nearly identical to the EE-108. It seems that these have been developed and used in the same timeframe. The TP-3-(*) instruments add an optical ringing indicator, a screw switch allows to choose between the built in ringer or a small neon light as ring indicator.
As the EE-8 (and a lot of other equipment) the EE-108 was distributed to WW2 allies under the lend-leaese program, mainly to the USSR (>70k). This EE-108 has signal corps stamps and a transmitter element from the 50ies, it seems to have been in use at the US signal corps at least up to the late 50ies. This (or all?) EE-108 was manufactured by the Connecticut Telephone and Electrical Company.
The instrument is sound powered, the transmitter does not need battery power. Instead of a carbon transmitter as in local battery field instruments this instrument uses an electromagnetic transmitter (and receiver), when talking the electrical power induced in the transmitter is sent to the line. The transmitter and receiver elements are interchangeable.
Ready for use
Disassembled
Wiring Diagram.
Schematic Diagram.
Body opened. Top left lightning arrestor. Ringer and capacitor below generator.
Body top. Handset connectors, T1, T2. Line connectors, L1, L2 and ground G. Line test button (If pressed and generator cranked ringer should sound when connected to working line with terminating instrument). Red signal corps inspection stamp.
Handset type TS-10-() with P.T.T. button. Elements removed. The paper capacitors mounted in the handset (0,05uF each, 2x at TX and 1x at RX side) improve the frequency response of the circuit.
RX and TX elements back. The RX element is from 43, the TX element from 56. According to the manual they should be interchangeable.
RX and TX elements front.
Crank handle unmounted.
Body mounted in cover. Handset cord connected and secured.
Handset stored. SC acceptance stamps inside cover lid.
Ready for transport or storage.
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