AE 40 railway dispatcher's telephone of the type N-4069

[unbeldi]

The Type 40 Monophone was a telephone design that Automatic Electric used for a wide variety of applications, and not only for standard telephone service.

The type N-4069 was a telephone set for railway communication systems, as a siding station perhaps, but more likely as a dispatcher's telephone for working at a desk.  AE made an equivalent version of this in the Type 60 format, which was a metal box mounted on a wall.

Although it uses a local battery to power the transmitter, calling it a local battery telephone is quite misleading. A standard local battery telephone places the receiver across the telephone line in series with the secondary winding of the induction coil and the transmitter signal is coupled into that loop with the primary winding of the coil. This type of circuit is illustrated in the diagram to the right (also last attachment). The railway station uses that same principle for the transmitter, but the line loop does not contain the receiver at all, but only the secondary winding of the induction coil. Thus the transmission circuit operates exactly like an AC power transformer, only in reverse.  The small voltage signal from the low-impedance transmitter is amplified onto the line which has a very high impedance due to the typically very long line to a neighboring station, perhaps tens of miles away.  The receiver is also coupled into that transformer with a separate winding.   This arrangement provides complete electrical isolation of the talk and listening side from the line. The first diagram of the attachments shows the circuit of the N-4069.  It clearly shows the just described circuit arrangement.  The transmitter and receiver circuits share one side of their respective circuits to use only one wire, connected to induction coil terminals 2 and 3, so that the handset needs only three wires in its cord, connected to terminals R, C, and T, just as is the case in any Type 40 Monophone.

The handset in this telephone is special.  It contains a push-to-talk button. This button must be pressed when the operator wants to speak and transmit.  Thus, the battery that powers the transmitter (terminals 3 and 4) is only connected when necessary. When the button is pressed, a 700 ohm resistance is also switched into the receiver circuit, eliminating sidetone.   The handset is not a Type 41 handset of the standard Monophone, but has a somewhat different, much more rounded shape. It appears similar to the Type 25 handset, but having a different type of switch than the Type 25 handset documented in AE catalogs.  I am not aware of any railroad equipment catalogs by AE, that would determine the type designation that AE used for this handset.  Because of this handset, the N-4069 telephone set is easily recognized when encountered. The third attachment shows a recent eBay observation.

The wiring diagram of these sets is label FORM D-53998-A. The attached image is Issue 5, which is also the basis of the circuit diagram in the first image.
This wiring diagram can still be found in the current inbox of the TCI library, but it is mislabeled as a local battery telephone and has no provenance.

Another notable feature is that the set contains no ringer.  The set could be used with an A.C. signaling system or with a DC driven system. In either case, the ringer was mounted on a wall in the station room.  In a DC system, typical of many US railway dispatch systems, the ringer was triggered by a relay that was driven by a step-by-step selector.  The dispatcher had another unit on his desk, a selector key.  This key sent a sequence of D.C. pulses onto the line which was decoded in all way stations connected to the line.  However, only one station was configured to respond to the signaling, and that would trigger the ringer relay.  The ringer was often powered from the same D.C. supply that also powered the transmitter.  In an AC signaling system, the ringer circuit is identical to a standard telephone, and is activated by a magneto generator.

Transmitter power to this desk set was brought into the set by two of the four-conductors in the mounting cord, as can be seen in the wiring schematic.

It is interesting to note that the type of circuit used in the N-4069 telephone is the same that Western Electric used in its railway station systems. In fact, AE made some small subsets that contained only the induction coil and the condenser, but which were designated to be used with Western Electric transmitter arms.


N-4069 Components
Induction coil: D-283022
Condenser: D-68270A, 0.5 µF

Observed patent decals: D-780504 A30

[unbeldi]

An equivalent instrument to the N-4069 in terms of application and function was found in this forum post, which presents a metal wall box with a fixed bulldog transmitter, to be used with a head set receiver.  The circuit is identical and used the same induction coil as the N-4069.  The diagram indicates that it was used with an A.C. ringing system.

The set was most likely built by an independent supplier of railroad communication systems.

[Doug Rose]

that was mine and I do have a much better one, pm me if interested....Doug

[AE_Collector]

Good job Unbeldi. Lots of good information.

Initially I thought there would likely be an AE50 version as well but maybe not since there was the Type 60 Railroad Wallphones.

This topic here on CRPF about AE Railroad Telephones has lots of good info about these systems and equipment from AE:
http://www.classicrotaryphones.com/forum/index.php?topic=15155.0

Terry

[unbeldi]

Good job Unbeldi. Lots of good information.

Initially I thought there would likely be an AE50 version as well but maybe not since there was the Type 60 Railroad Wallphones.

This topic here on CRPF about AE Railroad Telephones has lots of good info about these systems and equipment from AE:
http://www.classicrotaryphones.com/forum/index.php?topic=15155.0

Terry

Yes, I am aware of that thread.  I am planning on referencing that material in another post to bring all of these sets under one umbrella and provide some overview.

Indeed, I don't think we should be looking for a Type 50 set with these features, the Type 60 has at least two versions (catalog numbers) that do the same.