Australian Post Office
Telephone No. 333MT


In general appearance the new model Magneto Handset Table Telephone is the same as the C.B. and. Automatic type (332) except that a small hand generator is mounted in the dial Space in the moulded body of the instrument.
The telephone is a complete magneto unit except for a battery box.  The first deliveries will be the sidetone type, but future supplies will probably be the anti-sidetone type.

Base Plate
The sheet metal base plate which carries all the electrical components of the telephone is provided on its under side with four rubber feet and two metal cover plates.  One cover plate fits over a recess in which is mounted a moulded connection block for the instrument cords.  The other cover plate fits over an aperture in the base plate provided to enable the generator cut-out springs to be readily adjusted.

Instrument cords can be changed and the generator cut-out springs adjusted without removing the metal base plate from the telephone.  To remove the metal base plate from the telephone the generator handle is first removed by unscrewing the centre holding screw in the generator driving axle.  Then the four corner and two side captive screws are unscrewed, and the base plate carrying the components is readily removed.

Induction, Coil (Sidetone Type)
The 1 ohm plus 19 ohm induction coil which is of the open core type fitted with a moulded bobbin is mounted on the upper side of the base plate near the front.  The primary winding of the induction coil has 400 turns and the secondary 1300 turns. Future supplies will probably include an anti-side tone induction coil.  The Magneto Bell and Cradle Switch are similar to the, C.B. type.  The metal base plate at the rear is shaped to form a shelf which carries on its under side the moulded instrument Cord connection block and on a metal projection fitted to its upper side the magneto bell assembly and the cradle switch. The bell gongs are mounted on the upper side of the base plate directly in front of the metal shelf.

Hand Generator
The metal shelf projection also carries the small hand generator which is fitted with an “Alnico” permanent magnet.  The generator is mounted with its driving axle at an angle of about 50 deg. to the metal base plate.  When assembled in the telephone the generator driving axle to which the handle is fitted protrudes through the hole in the moulded dummy which is fitted in the dial aperture.  The generator is screwed firmly to the metal projection and the metal base plate by five holding screws.

The recent introduction of a new magnetic alloy, aluminium-nickel-cobalt-steel, “Alnico,” to replace tungsten steel formerly used in the manufacture of permanent magnets has resulted in the development of a telephone hand generator of an entirely new design. “Alnico” has the maximum flux density per unit of volume for any magnetic material yet discovered.  The specific gravity of the alloy is low also, giving a reduction in weight which is distinctly advantageous.

 

 
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Last revised April 02, 2010

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