Magnetic eraser with head winding as part of oscillator circuit

Claim 2

A magnetic eraser comprising an erase head provided with an erase coil; an oscillator for supplying the erase head with erase current and in which the erase coil is concurrently used as an oscillation coil; and a casing for receiving the erase head and oscillator, said oscillator comprising: a plurality of resistance elements connected in series across a power source; first and second transistors of different conductivity types each having a collector, emitter and base, the emitter of said first transistor being connected to the emitter of said second transistor, the collector of said first transistor being connected to one terminal of said power source to which there is connected a first of said resistance elements, the collector of said second transistor being connected to the other terminal of said power source to which there is connected a second of said resistance elements, a third of said resistance elements being connected in series between said first and second resistance elements, the base of said first transistor being connected to the juncture of said first and third resistance elements and the base of said second transistor being connected to the juncture of said second and third resistance elements; a first capacitor, one end of which is connected to said collector of said second transistor and the other end of which is connected through said erase coil to said emitter of said first transistor, thereby constituting a series resonance circuit with said erase coil; and a second feedback capacitor connected between the juncture of said erase coil and first capacitor and a point intermediate the ends of said third resistance element.

Claim 3

The magnetic eraser according to claim 1 wherein said oscillator is formed on a hybrid integrated circuit chip.

Claim 4

The magnetic eraser according to claim 1 wherein the elements of said oscillator other than said first and second capacitors are formed on a monolithic integrated circuit chip.

Claim 5

The magnetic eraser according to claim 1 including a recording bias current terminal coupled from the juncture of said erase coil and first capacitor.

Claim 6

The magnetic eraSer according to claim 1 wherein said oscillator comprises: a fourth resistance element connected between said first resistance element and one terminal of said power source; a diode stack connected between the juncture of said first and fourth resistance elements and said other terminal of said power source to which there is connected said second resistance element, said diode stack including a plurality of series connected diodes connected in the forward direction with respect to the polarity of said power source; and an additional diode connected across said first resistance element in an opposite direction to the polarity of said power source.

Claim 7

The magnetic eraser according to claim 1 wherein said resistance elements are individual resistors.

Claim 8

The magnetic eraser according to claim 6 wherein said third resistance element comprises the series combination of a pair of resistors, said intermediate point being the juncture point of said pair of resistors.

Claim 9

The magnetic eraser according to claim 1 which further comprises a thermistor connected in parallel with said erase coil.

Claim 10

The magnetic eraser according to claim 8 wherein said thermistor and oscillator are embedded in a potting compound.

Claim 11

A magnetic eraser comprising an erase head provided with an erase coil; an oscillator for supplying the erase head with erase current and in which the erase coil is concurrently used as an oscillation coil; and a casing for receiving the erase head and oscillator, said oscillator comprising: a plurality of resistance elements connected across a power source; first, second and third transistors each having a collector, emitter and base, said third transistor having a different conductivity type from that of the first and second transistors, the collector of said first transistor being connected to one terminal of said power source to which there is connected a first of said resistance elements, the emitter of said second transistor being connected to the other terminal of said power source to which there is connected a second of said resistance elements, the emitter of said first transistor being connected to the collector of said second transistor and the emitter of said third transistor, the collector of said third transistor being connected to the base of said second transistor, a third of said resistance elements being connected in series between said first and second resistance elements, the base of said first transistor being connected to the juncture of said first and third resistance elements, and the base of said third transistor being connected to the juncture of said second and third resistance elements; a first capacitor, one end of which is connected to the emitter of said second transistor and the other end of which is connected through said erase coil to the emitter of said first transistor, thereby constituting a series resonance circuit with said erase coil; and a second feedback capacitor connected between the juncture of said erase coil and first capacitor and a point intermediate the ends of said third resistance element.

Claim 12

A magnetic eraser comprising an erase head provided with an erase coil; an oscillator for supplying the erase head with erase current and in which the erase coil is concurrently used as an oscillation coil; and a casing for receiving the erase head and oscillator, said oscillator comprising: a plurality of resistance elements connected across a power source; first, second and third transistors each having a collector, emitter and base, said third transistor having a different conductivity type from that of the first and second transistors, the collector of said first transistor being connected to one terminal of said power source to which there is connected a first of said resistance elements, the emitter of said second transistor being connected to the other terminal of said power source to which there is connected a second of said resistance elements, the emitter of said first transistor being connected to the collector of said second transistor and the emitter of said third transistor, the collector of said third transistor being connected to the base of said second transistor, a third of said resistance elements being connected in series between said first and second resistance elements, the base of said first transistor being connected to the juncture of said first and third resistance elements, and the base of said third transistor being connected to the juncture of said second and third resistance elements; a first capacitor, one end of which is connected to the emitter of said second transistor and the other end of which is connected through said erase coil to the emitter of said first transistor, thereby constituting a series resonance circuit with said erase coil; and a second feedback capacitor connected between the juncture of said erase coil and first capacitor and a point intermediate the ends of said third resistance element.

Claim 13

The magnetic eraser according to claim 10 wherein said oscillator comprises: a fourth resistance element connected between said first resistance element and one terminal of said power source; a diode stack connected between the juncture of said first and fourth resistance elements and said other terminal of said power source to which there is connected said second resistance element, said diode stack including a plurality of series connected diodes connected in the forward direction with respect to the polarity of said power source; and an additional diode connected across said first resistance element in an opposite direction to the polarity of said power source.

Claim 14

The magnetic eraser according to claim 11 wherein said resistance elements are individual resistors.