Patent GB-487357-A (GB)
Title: Improvements in and relating to telephonic instruments
IPC: H04R11/00
Filed: 1937-03-31
Abstract: 487,357. Telephone instruments. CONTROL INSTRUMENT CO., Inc. March 31, 1937, No. 9135. Convention date, April 10, 1936. [Class 40 (iv)] A telephone instrument comprises a disc provided with a pair of substantially parallel, spaced plates extending at right - angles to the disc, the plates being connected at their tops by spaced cross-bars and having recesses extending downwardly between said bars and other recesses extending upwardly in alignment with the downwardly - extending recesses, upper and lower polepieces fitting and secured within the respective pairs of recesses of the plates, a coil positioned between the downwardly and upwardly extending poles of the respective polepieces and an armature passing through the coil and between the poles. The disc member 4 is mounted on an apertured cylindrical base 2 and is formed with integral parallel plates 6, 7 connected at the top by integrally formed cross-bars 8, 9. The plates are formed with recesses 10, 11 and 14, 15 and apertures 12, 16 through which the armature passes. The polepieces 19, 36, Fig. 12, are shaped to co-operate with the recesses 10, 11 and 14, 15, and the lower polepiece 19 is formed with channel recesses 25, 26 in which are located clamping bars 22. 24 secured by screws 27 threaded into the lower surface of the member 4. The upper polepiece 36 is similarly formed with channels 41, 42 in which are seated clamping bars 39, 40 which, together with an insulating terminal plate 44, are secured to the bars 9, 10. The leads from the coil 30 are soldered to bars 46, 47 provided with connecting screws 50, 51. The coil 30 is carried by a moulded spool 31 fitting tightly between the poles 28, 29 of the polepiece 19 and the poles 37, 38 of the polepiece 35 and provided with recessed portions 32, 34 having a width equal to that of the polepiece. The permanent magnets 68 which are of a length to fit tightly between the plates 6, 7 are retained by brackets 71, 72 so that their end surfaces 69, 70 are in contact with the polepieces 19, 36. The armature 59 and polepieces are preferably of laminated form, and, as shown in Fig. 16, the armature comprises outer laminations 80 of Swedish iron to provide high permeability and a centre sheet 81 of silicon steel for high resistivity. The laminations 80, 81 are separated by a layer of cement, preferably a phenol condensation compound, in which the armature is also encased. Fig. 14 shows a construction of polepiece in which the outer and central sheets 75, 76 are of silicon steel and the intervening laminations 77 are of Swedish iron. The laminations and sheets are held together by nickel rivets 78, 79 passing through holes which are differently located relative to the longitudinal edges of the polepiece to facilitate a more accurate assembly. The armature 59 is supported at its fixed end between plates 64, 65, Fig. 17, secured by a screw 66 to a U-shaped plate 60 which has a V-shaped rib 62 co-operating with a similarly shaped recess 18 in the plate 7. The plate 60 is formed with smooth holes 61 through which pass screws 67 which secure the plate 60 to the plate 7 and by which the position of the armature 59 in the gap 35 can be adjusted. The free end of the armature is connected by a rod 84 to a diaphragm 57 mounted between clamping rings 55 and retained by a ring 58 in a screwthreaded recess formed in the bottom of the base 2. The clamping rings 55 are formed with lugs 56 co-operating with notches 54 in the recess to prevent transmission of rotational stress to the diaphragm when the retaining ring 58 is screwed into position.