Patent GB-798928-A (GB)
Title: Improvements in and relating to broad band magnetic tape recording and reproducing systems
Inventor: GINSBURG CHARLES PAUSON
IPC: H04N5/782
Filed: 1955-09-16
Abstract: 798,928. Automatic speed control systems. AMPEX CORPORATION. Sept. 16, 1955, No. 26639/55. Class 38 (4). [Also in Group XXXVIII] A broad band magnetic tape recording and reproducing system for wide signal frequency spectrum use including, e.g., video frequencies, comprises a rotary head assembly 27, 28, Fig. 1, including a plurality of magnetic transducer units 34, Fig. 3, arranged to sweep successively across the tape 11, two A.C. synchronous motors 23, M for respectively rotating the head assembly and a tape transporting capstan 17, a pulse generator 24 rotating with the head assembly to generate a signal of frequency directly dependent upon the rate of head assembly rotation, and phase comparitors 87, 99 which correct and maintain constant the speeds of the two motors. During recording and reproducing the motor 23 which drives the head assembly either directly or through belt and pulley stepdown gearing 56 ... 58 is supplied from a reference frequency source 93 and the pulse generator signal is fed through a cathode follower tube 71, a frequency divider 77 to reduce its frequency to that suitable for the motors, and a wave-shaping filter 78; the source and signal, rendered of the same amplitude in amplifiers and clippers 91, 92 are fed into the phase comparitor 87 whose output feeds over a low-pass filter 88, reactance tube 86, variable oscillator 84 and power amplifier 83 to the motor 23, a current of frequency which corrects the motor speed, e.g. should the driving belt 56 slip. The tape motor M during recording is fed through a power amplifier 79 and a change-over switch S1 from the filter 78 to rotate in correspondence with the speed of the head assembly. During recording, the generator pulses are also fed over a filter 81 and an amplifier 82 to a head 19 which records them along a margin defined by 162, Fig. 11, of the tape, and during reproduction for which switch S1 is changed to its lower contact, these pulses are reproduced by said head 19 to control the tape driving motor speed to be the same as that during recording, reproducing any slight speed variations; to this end the reproduced pulses and the generator pulses are fed through amplifiers and clippers 101, 102 to the phase comparitor 99 whose output leads to motor M through similar circuitry 98, 97, 96, S1, 79 to that of motor 23. In its travel from a supply reel 12 to a tape up reel 13 the tape 11 is guided through the head assembly 27, 28 by flanged studs or rollers 14, 16. Another magnetic head 18 is provided to erase with A.C. the signals recorded by control head 19 or the one margin defined by 162 of the tape, while to operate on the other margin defined by 163 of tape are provided a sound recording and reproducing head 21 and a corresponding erase head 20. The magnetic head assembly comprises, mounted upon a shaft 31, Fig. 3, driven by the motor 23, a rotatable member 29 whose annular rim 32 has a plurality of tapered slots 37 each carrying a magnetic transducer unit 34 which comprises, not shown, embedded in a solid synthetic resin body U-shaped magnetic core pieces having windings and pole tips 36 spaced by a thin non-magnetic gap, not shown. Except for an access slot 45, the enclosure of the member 29 by shell portion 28 is completed by a guide 46 whose inner arcuate surface 47 has a groove 54, Figs. 3 and 5, opposite the pole tips 36 so that the tape by not being directly supported may deflect slightly in this region, and grooves 51 to which may be connected a suction tube 53 whose evacuation ensures physical contact of the tape with the guide surface. The tape is supported against movement in the direction of head rotation by hook-shaped abutments 48 carried by guide 46 and accommodated in grooves 49 in the periphery 33 of member 29, 32. The windings 1 ... 4, Fig. 9, of the transducer units 34 are each connected at one end through a silver button, not shown, on the shaft 31 to a grounded graphite brush and at the other end to a respective slip ring or in pairs to slip rings, contacted by a brush leading through terminal leads T1 ... T4 to recording and reproducing channels which together with the light actuated pulse generator 24 are described in Specification 798,927, [Group XXXVIII]. Specifications 798,929 and 798,930, [both in Group XXXVIII], also are referred to.