Author Topic: AE 40 local battery circuit of the type N-4071 desk set with DC signaling  (Read 228 times)

unbeldi

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In this post user stub reported in 2013 the finding of a local battery telephone set in the style of the Type 40 Monophone by Automatic Electric.

The type designation (order number) of the set is N-4071.   Its wiring schematic that is usually glued inside the set is labeled FORM D-530000-A. It is shown in the second attachment.

The circuit diagram of the set is the first attachment.  It shows a fairly standard local-battery circuit with an anti-sidetone induction coil.  It is drawn in the on-hook state. Note that Automatic Electric always drew their wiring diagrams in the talk state, off-hook.

The transmitter (TX) is in series with the primary winding (P) of the induction coil, and is powered by a 3 V battery supplied through the mounting cord.  The hookswitch closes the transmitter circuit.

The receiver (RX) circuit bridges across the line (L1, L2) and includes the secondary winding (S) of the induction coil. The receiver circuit is also closed by the hookswitch when going off-hook. The transmitter and receiver circuits share one leg each at terminal C, so that the handset can be wired with only a three-conductor cord.

The sidetone cancellation is accomplished with a third winding (T) of the induction coil which includes an ohmic balancing network, that is connected in parallel across the receiver, just as is done in the standard common battery configuration of other Monophones.

A notable feature of the N-4071 telephone set is the presence of a signaling push button.  This button connects a 22.5 V battery to the line to activate a signal or buzzer at the CO switchboard or PBX.  Capacitor C1 (1 F), between this signaling circuit and the rest of the telephone prevents DC injection into the receiver.  This battery must be provided at the installation location of the substation, in addition to the 3V talk battery,

The capacitor also serves as a ringing capacitor for the low-impedance ringer, and thus also prevents the local ringer ringer from draining the signaling power. It may cause a short bell tap, if the biased ringer polarity is not coordinated with that of the battery.

The patent label of these sets is # D-780503 A30, which is used for other local battery telephones by AE as well.  It only shows patents one would expect on a non-dial telephone.
US2149628 1939 1935 Pye AEL--Telephone Transmitter
US2205669 1940 1938 Pye AEL--Sound Translating Device
US2205670 1940 1938 Pye AEL--Sound Translating Device (receiver)
US2205906 1940 1938 Obergfell AEL--Sound Translating Device supporting Assembly (handset)
US2272474 1942 1938 Obergfell AEL--Telephone Substation Apparatus (telephone set components)
USD117876 1939 1938 Obergfell AEL--Design for a Telephone Desk Stand (AE40 design)

This was not the only telephone set for local battery service in the form of the Type 40 Monophone.  AE also made other sets, including one that could be converted between LB and CB service, which may be seen in this post for the Type N-4078 Monophone.
« Last Edit: March 08, 2017, 09:11:35 PM by unbeldi »