Patent GB-670577-A (GB)
Title: Magnetic recording and reproducing
IPC: G11B5/00
Filed: 1947-11-28
Abstract: 670,577. Magnetic sound recording and reproducing apparatus; magnetic records. BRUSH DEVELOPMENT CO. Nov. 28, 1947. [Dec. 4, 1946] No. 31544/47. Class 40 (ii). In a magnetic recording and reproducing apparatus provision is made for preventing inadvertent erasing of or recording on commercial records desired to be kept intact. In Fig. 1A, a record track guide structure is shown having an outer wide path 169 and inner narrow path 161 for wide commercial, and narrow home, tape respectively, diverging apart before the erasing and recording heads 43, 44 and only meeting in front of the reproducing head 45. A sensing member 140, Fig. 2, may be contained in the narrow path so that only when the latter is occupied by 'home' tape 31 is the sensing member operated to close a switch 156 permitting the supply of erasing and A.C. biasing flux from an oscillator to the erasing and recording heads. The heads 43, 44, 45 are mounted'in recesses of the guide structure and have opposed enclosing members 190, Fig. 7, with bosses 192, one of which projects through an over large opening in the base of the recess to permit their adjustment before a clamping plate 200 secures them in position. Pads 120 controlled by the recording switch through electrical or mechanical linkage against spring action may press the tape against the erasing and recording heads. In a modification, Fig. 10 (not shown), recording and reproducing is effected on one transducer and the guide member is separate and has laterally adjacent wide and narrow grooves, one containing the sensing member. In a further modification, Fig. 12, the commercial tape reels have a blocked hub arranged to depress a rod otherwise projecting through the hub and thereby to operate a control switch 98, all tapes then having the same width. In a still further modification, a guide structure is formed of two conducting sheet members separated by insulation and one type of tape arranged to be surfaced on the side opposite the magnetisable side with a conductive coating bridging the insulation and operating a switch, or the leading portion only may be made conducting and operate a self-locking relay only released when a reeling limit switch is operated or the record is reversed for rewinding. Alternatively, tape formed with altered light reflecting properties produced by coatings or perforated along one edge in conjunction with a photo-cell may be used. Alternatively, for erasable recording, an additional signal of frequency outside the frequency response of a playback unit may be superimposed on the recording and used during playback to produce a control signal. In a further modification, Figs. 15, 16 (not shown), a sensing device is recessed in one lateral half of a wide channel, and the heads aligned with this lateral half so that both the wide and narrow tapes engage all the heads but only the narrow tape operates the sensing member and the wider form of tape used has two lateral records, each playable in turn by interchanging the supply and rewind reels. The Specification, as open to inspection under Sect. 91, refers to the use for home recording of dielectric tape which generates a control signal from the oscillator supplying erasing and A.C. biasing flux. This subjectmatter does not appear in the Specification as accepted.