GB535927A - Improvements in telegraphones - Google Patents

Abstract

535,927. Telegraphones. ELECTRICAL RESEARCH PRODUCTS, Inc. May 21, 1940, No. 9003. Convention date, July 29, 1939. [Class 40 (ii)] In making a telegraphone record, the record strip 1 is first subjected by pole pieces 2 to an erasing alternating magnetic flux of frequency higher than any to be recorded and then by other pole pieces 3, to the recording magnetic flux accompanied by an alternating magnetic flux of higher frequency than the erasing flux but of lower intensity. As shown, the. alternating fluxes are produced by alternating currents derived from a single thermionic oscillator 7 rich in harmonics. The fundamental frequency of this oscillator is fed through a condenser 10 to the coil 9 of the pole pieces 2, the condenser and the coil being tuned to accept this frequency. The third harmonic is supplied to the coil 15 of the pole pieces 3 through a condenser 17, an,adjustable resistance 16, the coil and the condenser being tuned to accept this harmonic, and a coil 22 and condenser 23 tuned to the fundamental being interposed between the oscillator and the condenser 17 to choke off the fundamental. These devices can be connected for recording or reproducing by means of a switch 4. In the recording position, power from source 5 is fed through choke 24 to oscillator 7, and microphone 11 is connected through amplifier 12 to coil 15. In the reproducing position of the switch 4, the microphone and the oscillator 7 are cut off, and the coil 15 is connected through equalizing circuit 18 to amplifier 12, the output of which is then connected to a loudspeaker 19.