The British Ericsson Magneto Wall Telephone

Rod Williams

In 1916, the Australian Post Office chose the British Ericsson Magneto Wall telephone to be their standard telephone to replace the then standard Commonwealth Swedish Ericsson 131 M.W. This new telephone was very different from the ornate Commonwealth model.

It was constructed as follows: An oak case, measuring 415 mm. high x 240 mm wide and 150 mm deep. The generator, magneto bell, switchhook spring set, induction coil, together with 2 dry cells are mounted in the wooden case which had a full length door opening right to left. Mounted on this door was the magneto bell, also a 'White' solid back transmitter and a writing slope. On the right hand side of the case was the generator handle and an 8mm hole for a cord to attach an additional receiver, if required. On the left hand side of the case was a bell receiver. Wiring terminals and mounting screw holes were hidden.

This telephone was known as a 35 M.W.

Figure 1 (Above): Front view of a 35MW

Figure 2 (Above): (Left) Side view showing hole/grommet for additional receiver. (Right) Inside view of 35MW

 

Figure 3 (Left): Cross section of solid back transmitter (No. 1)

 
Figure 4 (Left): Schematic diagram of 35 MW

 

 

After a short time, early 1920's, the solid back transmitter was replaced with an Ericsson inset transmitter which was housed in a brass drum. This drum could be rotated through 360 degrees to free-up the carbon granules in the inset cartridge when they packed together in time, through use. This packing of granules caused a decrease in transmission efficiency.

 

Figure 5 (Above): The Drum transmitter model of the British Ericsson.

Figure 6 (Left): Cross section vies of (a) Insert capsule and (b) Drum transmitter

 

 

In approximately 1930, the transmitter was again replaced, this time with the new inset transmitter, No.10 cartridge, housed in a bakelite mounting and coded Telephone 135MW.

 

The table model for this time was the 36 MT / 136 MT, pedestal telephone, together with bellset No.5 M, hand generator No.1 and a wooden battery box.

The above models all used induction coil No.12 (see Figure 16).

Figure 7 (Above): The Bakelite transmitter model of the British Ericsson. Note the difference in the mount to the Drum transmitter model.

Figure 8 (Left): Cross section view of No. 10 insert capsule - this is fitted inside the bakelite housing.

 

 

 

 

Figure 9 (Left): 136MT candlestick.

 

Figure 10 (Right): No5 Bell set and No1 Hand Generator unit for 136MT

 

Modified British Ericsson for Automatic Working with Rural Automatic Exchange Long Lines

A telephone that stayed in our Rural Automatic Exchange installation store, and never put to use, was the telephone 765 / AT / C.B.T / AW /CBW. This was a telephone, for long lines, which had a local battery supply, 2 cells, with the option of a third cell, if necessary, to boost the transmitter power. It came fitted with a dial, also an Ericsson 4 bar hand generator and used induction coil No.15 (see Figure 16).

Remember to this point in this article, the A.P.O. did not have a handset telephone.

 

Above: Schematic diagram of 765AT/CBT/AW/CBW.

Figure 11 (Above): The765 with dummy plug.

Figure 12 (Above): The 765 with fitted dial.

 

The Lead-up to the Handset Modification to the British Ericsson

The year 1932 saw the APO adopt a handset telephone, designed in 1929 by Siemens Brothers, with a black Bakelite case and even though it was a table model, it was also used as a wall telephone when mounted on a wall bracket. This new model, when used for magneto working, used a local battery for the transmitter circuit, a hand generator, No.4CN, for signalling, a steel battery box and coded telephone 162 MW when wall mounted. The induction coil for magneto working had a 1 ohm primary coil and a 15 ohm secondary coil (no induction coil number) and the automatic version used induction coil No.18 (see Figure 16).
At the beginning of 1939, there were 270,000 magneto telephones in service, and 55,000 were of the handset type introduced in 1932, 15,000 being wall instruments and 40,000 the table type. The net increase per month in magneto handset wall telephones was about 450. Due to the replacement of magneto equipment by automatic type and the demand for handset instruments, magneto wall telephones were being returned to stores throughout the Commonwealth at the rate of about 1000 per month; of these about 600 per month were the British Ericsson wall type. Most of the telephones so returned would not normally be used, as the main demand of new local battery installations was for handset types. At this stage,remember that the standard magneto wall handset telephone was a table model 162, with its' associated bellset mounted on a black enameled steel wall bracket, with a generator fitted in a wooden case and a black steel battery box, but still no Anti Side Tone Induction Coil.

Figure 13 (Above): Hand generator No. 4CN & 162MT. Note - PMG issued wall mount.
The anti-sidetone principle reduces the volume of input speech which is heard in the receiver of the transmitting telephone, that is, the person speaking will not hear his own voice so loudly, and external noises in the room will not enter the transmitter and come back into the receiver to the same extent as previously. The speaker therefore hears less 'side tone' in his own receiver when he is speaking and while this adds to his comfort, it causes him to raise his voice slightly and the person at the other end hears him more clearly

In 1939, the Post Master General's Department refurbished and modified the recovered British Ericsson wall sets as follows:

  1. The case was repaired and the surface polished.
  2. The components were removed from the case, reconditioned as necessary and returned to the case.
  3. The holes left with the removal of the transmitter mount were covered with a notice on how to use the telephone.
  4. A clip was added to the writing slope.
  5. The bell receiver was replaced by a black moulded handset with a 3 ft. 6 ins. black cord.
  6. The switch hook rest was replaced with a receiver hook "M" and bent to prevent the tip of the mouthpiece hitting the wall when on the rest.
  7. The two-winding induction coil No.12* was saved and rewound with 4 windings, 3 inductive and 1 non inductive. An extra terminal was attached to each of the cheeks of the coil-former to accommodate the new windings.
  8. A new circuit was designed.

This telephone was designed to use two dry cells. When used on subscribers' lines longer than 3.2 miles of 10 lb. cable, or 4.6 miles of 20 lb. cable, 3 dry cells were fitted to improve the sending efficiency of the transmitter.

This new telephone, coded 235 MW, was the first magneto wall telephone to have an A.S.T.I.C. (induction coil No.21A (see Figure 16)) and this was the new standard handset magneto wall telephone.

 

Figure 14 (Above): 35MW

 

 
Figure 15 (Left): Schematic for 35MW

Figure 16 (Above): Induction coils used in early PMG telephones, and samples of induction coils used in British Ericssons. (click the image to see an enlargement)

 

References

Reference material for this article was sourced from:

  1. P.M.G. Substation Telephone Equipment Circuits, Facilities and Stock Titles, issued 1951.
  2. The Telecommunication Journal of Australia February 1939. (They refer to the B.E. as a 233MW, which is incorrect, as that code is for a Stromberg Carlson modified in the same way as the British Ericsson.)

 

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