Abstract: A method and apparatus for determining and for reducing magnetism in a generator stator core (20). The method includes extending one or more conductors (38) proximate the core, applying a polarity-reversing excitation voltage to the one or more conductors, and reducing an amplitude of the voltage over time, wherein the voltage causes current to flow in the conductors, the current generating a magnetic field that demagnetizes the core. The method and apparatus are useful for determining hot spots in the core.

Abstract: Provided is a coercive-force specifying apparatus capable of creating a demagnetization curve for each divisional area of a coercive-force distributed magnet without breaking the coercive-force distributed magnet and of specifying an average coercive force for each divisional area precisely. A coercive force specifying apparatus of the present invention includes: a yoke including an insertion space into which a coercive-force distributed magnet is to be inserted; a magnetizing coil; a search coil that detects a magnetization change when the magnetic field is applied to the coercive-force distributed magnet; and a tracer that creates a demagnetization curve on a basis of a voltage value generated due to the magnetization change. The end face is provided with two or more loop-shaped thread grooves bored therein, the search coil being provided in each thread groove.

Abstract: There is provided a coercivity performance determination device for a coercivity distribution magnet that is capable of determining, in a short period of time, with precision, and at as low a testing cost as possible, whether or not each part of one coercivity distribution magnet has a coercivity that is equal to or greater than the required coercivity. A coercivity determining device of the present invention comprises: a substantially C-shaped magnetic body; excitation means that generates a magnetic flow in the magnetic body; and a flux meter that measures the residual magnetic flux of the coercivity distribution magnet. Protrusions are provided at corresponding positions on two opposing end faces of the magnetic body, and the coercivity distribution magnet is held between the two protrusions to form an annular magnetic circuit. An external magnetic field generation means is formed by magnetic regions caused by the protrusions and non-magnetic regions comprising the air in the periphery thereof.

Abstract: According to the present invention, a method for determining coercivity of a coercivity distribution magnet, whereby coercivity of each portion in the coercivity distribution magnet can be determined with good accuracy without, for example, cutting the coercivity distribution magnet into pieces and thus quality assurance can be achieved with good accuracy, is provided.

Abstract: The present invention relates providing a magnetic data eraser that is capable of performing magnetizing process for magnetizing magnetic recording medium such as a hard disk drive (HDD) is easily and with reduced electric power. The magnetic data eraser includes: holding drawer means for holding a magnetic recording medium which means has a mounting tray for mounting the magnetic recording medium, wherein the mounting tray is inclined a predetermined value of degrees of angle; and magnetizing means for magnetizing the magnetic recording medium, wherein the magnetizing means is covered by a magnetizing coil and has a hollow body portion, the holding drawer means being accommodated in the hollow body portion, and the magnetic recording medium being placed on the mounting tray of the holding drawer means.

Abstract: A method and apparatus for determining and for reducing magnetism in a generator stator core (20). The method includes extending one or more conductors (38) proximate the core, applying a polarity-reversing excitation voltage to the one or more conductors, and reducing an amplitude of the voltage over time, wherein the voltage causes current to flow in the conductors, the current generating a magnetic field that demagnetizes the core. The method and apparatus are useful for determining hot spots in the core.

Abstract: A bulk erase tool to erase a perpendicular media recording (PMR) disk of a disk drive is disclosed. The bulk erase tool comprises a housing to receive a disk drive and at least one of a first pair of magnets mounted in the housing to be positioned above the received disk drive to provide a magnetic field to erase the top side of the disk and a second pair of magnets mounted in the housing to be positioned below the disk drive to provide a magnetic field to erase the bottom side of the disk.

Abstract: A magnetic data eraser includes a holding drawer means for holding a magnetic recording medium which means has a mounting tray for mounting the magnetic recording medium, wherein the mounting tray is inclined a predetermined value of degrees of angle. The magnetic data eraser further includes a magnetizing means for magnetizing the magnetic recording medium, wherein the magnetizing means is covered by a magnetizing coil and has a hollow body portion. The holding drawer means being accommodated in the hollow body portion, and the magnetic recording medium being placed on the mounting tray of the holding drawer means.

Abstract: An apparatus and method for preconditioning a magnetic recording disk is provided in which two substantially identical, but opposing, pancake coils are disposed generally parallel to one another with a gap therebetween into which a disk to be preconditioned is inserted. A large pulse of current is delivered to the coils to generate a magnetic field that is sufficiently strong to precondition the disk. The radial fields of each respective pancake coil add together in the gap where the disk is located, and the field presets both the data layer and the hard bias layer of the SUL. Outside of the gap region, the fields cancel one another such that there are essentially no perpendicular fields due to the symmetry of the coils, such that there is very little net residual perpendicular magnetization when the disk is removed from the gap. An electrical circuit for producing the current pulse is provided. An aluminum support structure provides thermal management and magnetic flux conductivity for the system.

Abstract: There is disclosed a method and system for demagnetizing an object. The method includes the step of applying a substantially uniform electromagnetic field to a magnetized object under condition to substantially demagnetize said object.

Abstract: A method for erasing a disk of a hard disk drive. The method includes moving the hard disk drive adjacent to an erasure head that emanates a magnetic field. The magnetic field and moving hard disk drive cause a disk of the hard disk drive to spin under a Lorentz force created by the magnetic field and moving disk. The magnetic field is applied by the erasure head for a duration that causes erasure of the entire disk. The spindle motor is not activated during the entire process. Not activating the spindle motor eliminates any Faraday coupling from the erasure head into the motor.

Abstract: An apparatus for demagnetizing a shadow mask includes a shadow mask stocker, a cassette in the shadow mask stocker, wherein at least one shadow mask is disposed in the cassette, and a demagnetizing device that generates a magnetic field by an alternating current (AC), thereby removing magnetism of the at least one shadow mask.

Abstract: Embodiments of the invention relate to erasing data recorded on a magnetic disk with increased certainty by using an external magnetic field. One embodiment is directed to a method for erasing data recorded on a magnetic disk, which is housed in a magnetic disk drive, by using an external erasure magnetic field generated by an external erasure magnetic field generator. The method comprises the steps of: moving a first magnetic disk drive within an external erasure magnetic field in a moving state appropriate for the type of the first magnetic disk drive, and erasing data recorded on a magnetic disk in the first magnetic disk drive; and moving a second magnetic disk drive, which differs in type from the first magnetic disk drive, within an external erasure magnetic field in a moving state that differs from the moving state of the first magnetic disk drive, and erasing data recorded on a magnetic disk in the second magnetic disk drive.

Abstract: A canceling exciting coil is supported by a coil supporting member of electrically insulating material fitted to an arch core. A canceling current Ic of opposite phase to a main current I flowing in the magnetic field generation circuit of the exciting coil by means of an exciting circuit is made to flow in a canceling magnetic field generation circuit provided with a canceling exciting coil, and generates canceling flux Mc. The idle component of the AC voltage generated in the canceling exciting coil is minimized by changing the number of turns n, coil inner area, and winding distribution of the canceling exciting coil, and adjusting canceling current Ic.

Abstract: A magnetic guiding apparatus guides a moving member by attracting a target with electromagnets provided on the moving member. The magnetic guiding apparatus has a magnetic-flux detection device movable along the target to detect magnetic flux of the target and a position measuring unit measures the position of the magnetic-flux detection device. A control unit detects the position of magnetic flux in the target from the position information obtained by the position measuring unit and the magnetic-flux information obtained from the magnetic-flux detection device and performs demagnetization at the detected magnetic flux position.

Abstract: A method is provided for preserving the transverse biasing of a GMR (or MR) read head during back-end processing. In a first preferred embodiment, the method comprises magnetizing the longitudinal biasing layers of the read head in a transverse direction, so that the resulting field at the position of the transverse biasing layer places it in a minimum of potential energy which stabilizes its direction. The field of the longitudinal biasing layer is then reset to the longitudinal direction in a manner which maintains the transverse biasing direction. In a second embodiment, a novel fixture for mounting the read head during processing includes a magnetic portion which stabilizes the transverse bias of the read head. The two methods may be used singly or in combination.

Abstract: The method according to the invention for demagnetization is effected in two separate steps. Firstly magnetically hard locations, such as weld seams, pressure locations etc., of an object to be demagnetized is pre-treated locally with high fields by way of choke coils in an alternating field. These magnetically hard locations are at least partly demagnetized by way of this. Subsequently the complete demagnetization is effected in a decisive second step. The object remains for a certain time in an alternating field. Now the alternating field is stepped down in that the current in a series oscillation circuit is stepped down in a current-controlled manner with two coils.

Abstract: In a soldering method for soldering an electronic component including a palladium or palladium alloy layer formed on a surface of the electronic component and also including a soldering lead terminal onto a printed wiring board including a soldering land and plated through hole, a solder layer containing tin and zinc as main components is formed on the surfaces of the land through hole by a HAL treatment. The lead terminal is inserted and mounted in the through hole. The printed wiring board is brought into contact with jet flows of a solder containing tin and zinc as the main components to thereby supply a solder to the land and through hole.

Abstract: A bulk degaussing system for the erasure of magnetic storage media by means of permanent magnets. The bulk degaussing system includes a rotatably mounted carousel and an angular displacement means that angularly displaces the carousel through a predetermined angle after passage of the carousel through a degaussing gap.

Abstract: Demagnetizing magnetic media for recording data in a data storage device includes placing the magnetic media in a magnetic field at a first strength, and gradually reducing the magnetic field to a second strength to essentially eliminate net magnetization in the magnetic media.

Abstract: A manually operated continuous-use desk-top magnetic media eraser/degausser that utilizes elaborately shielded state-of-the-art Rare Earth Magnets to uniformly remove magnetically recorded information from audio and video tapes, PC diskettes, and many other types of magnetic media that can be accommodated by the component's 1.0625 inches high by 4.125 inches wide media transport pathway. The media, as it traverses the pathway, passes through a very strong magnetic field created by two powerful grade N40 (40 MGOe) patented neodymium (NdFeB) permanent magnets placed perpendicular and end-to-end under the center of said pathway. As the recorded media is manually manipulated through the pathway, over the magnets, and out the exit, magnetic information stored on said media is removed by the strong magnetic lines of force present within the protective triple-shielded top, bottom, and side components surrounding the transport pathway.

Abstract: The invention applies to the neutralizer for electromagnetic raying, particularly harmful raying, caused by electro-magnetic fields from electric lines, installations, machines, appliances and apparatus. It includes cylindrical body (1) with semi-circular external groove (2) and two cylindrical chambers (4) in which over bar core (5) solenoids (S) are movably circled on. Chambers (4) are hermetically firmly closed by thread plugs (6). The bit of the invention is found in the fact that the difference in electrical potentials between the body (1) and the solenoid (S) brings to the weak electric field of high frequency, that annuls the effect of technical raying of low frequency, thus originating beneficial raying in its environment. This is achieved by the way that on cylindrical body (1) integrally done are concentric disks (11) with outer rings (111) and inner rings (12) between them.

Abstract: The object of the present invention is to provide a method and apparatus configured to allow an externally generated magnetic field to simultaneously erase a portion of the information on a disk, or a plurality of disks, within a magnetic storage device. The invention allows high throughput of erased magnetic storage devices, as in a mass production environment. Additionally, the invention allows a variety of magnetic storage device configurations in that the erasing is non-intrusive to the housing of the magnetic storage device and does not depend on the number of disks within the magnetic storage device.

Abstract: A portable, battery-operated AC electromagnetic yoke for detecting surface defects in ferrous materials by employing an AC magnetic field. The yoke includes a circuit that produces a quasi AC square wave voltage. The resulting AC magnetic field is the required inspection method of common practice and is capable of demagnetizing upon completion of inspection. A first bank of batteries supplies approximately sixty volts positive DC and a second bank of batteries supplies approximately sixty volts negative DC to power transistors that are in electrical communication with the yoke. Logic circuitry is employed to switch the respective banks of batteries on and off to simulate an AC circuit. The logic circuit includes a clock for generating pulses that are fed to a phase splitter circuit and to a delay and pulse shaping circuit. The respective outputs of those circuits are fed to logic gates that are in electrical communication with a voltage level shifting circuit that triggers the power drivers.

Abstract: A novel control circuit for magnetizing and demagnetizing an electric permanent chuck includes a single alternating current source with a selected frequency and phase. A circuit that generates electrical pulses is coupled to the alternating current source to produce pulses at a multiple of the frequency of the alternating current source. The pulse generating circuitry also sets the phase of the pulses relative to the phase of the alternating current source at a predetermined value. The pulses are then applied to the gates of one or more silicon controlled rectifiers (“SCRs”) which control current flow through the electric permanent chuck. By adjusting the phase of the electrical pulses, the amount of current and average DC voltage applied to a coil of the electric permanent chuck through an SCR can be controlled.

Abstract: A method and apparatus for establishing and maintaining a preferred induction level in a magnetic body. A varying voltage is applied to a conductive winding (61) that magnetically interacts with a magnetic body (60). The voltage is controlled during a first phase in such a way that the magnetic induction level of the magnetic body is changed from an unknown induction level to a known induction level. During a second phase, the induced voltage across the winding is controlled so that the induction level is changed from the known induction level to the preferred induction level. An optional third phase may be utilized, during which the average value of induced voltage is kept near zero in order to keep the induction level near the preferred induction level. The invention is especially applicable to ordinary current transformers, which may be demagnetized automatically while remaining in service.

Abstract: A method and apparatus for treating an object includes generating a magnetic field wherein at least some of the magnetic field is characterized by changes in amplitude of the magnetic field from an average non-zero value of the magnetic field. The object is placed in the influence of the magnetic field for a sufficient time to subject the object to the changes in amplitude of the magnetic field. A method and apparatus for determining a preferred field intensity of the magnetic field is also included.

Abstract: An information recording disc demagnetization apparatus according to the present invention demagnetizes information recording discs whose information is read by irradiating a laser beam, such as a music CD (audio compact disc), a photographic CD, DVD, MD, etc. The demagnetization process performed by the apparatus of the present invention successfully recovers tone quality, image quality, and the like, of the information recording disc, all of which are deteriorated by magnetism attained by the disc during reproduction of the disc.The information recording disc demagnetization apparatus has a disc-shaped air-core coil for creating an alternating magnetic field having a decremental intensity, and a means for holding the information recording disc in a stationary state within the alternating magnetic field.

Abstract: There is provided a magnetic recording/reproducing apparatus which has an improved reliability for a reproduced signal by eliminating a deformation in a reproduced signal waveform due to a residual magnetization generated in a magnetic head. The magnetic recording/reproducing apparatus has a magnetic recording medium including a magnetic film to which information is magnetically recorded and a thin-film magnetic head including a magnetic pole and a coil provided around the magnetic pole. A current supplying circuit supplies a current to the coil so that a magnetic state of the magnetic pole is stabilized. The current is supplied to the coil after a recording operation has been completed by the thin-film magnetic head. The current may demagnetize the magnetic pole of the magnetic head, or stabilize the magnetic state of the magnetic pole.

Abstract: A holder having at least one magnetizable body surrounded by a coil is demagnetized by passing through the coil a succession of groups of pulses. The pulses of each group are of the same polarity and the polarity of each group of pulses is opposite that of the preceding group while the current of the pulses of each group is less than that of the pulses of the preceding group. Each group has 2 to 8 identical pulses and the pulses are formed by clipping an incoming alternating-current line voltage.

Abstract: An improved electromagnetic chuck which does not require a continuous direct current supply while being magnetized, including a main body defining a plurality of recesses and forming a cover, which includes a plurality of magnetically conductive portions and non-magnetically conductive portions alternately arranged, a plurality of magnetic units arranged within said plurality of recesses, and a magnetizing/demagnetizing circuit for magnetizing/demagnetizing said plurality of magnetic units, is provided. The magnetizing/demagnetizing circuit includes a magnetizing circuit, a demagnetizing circuit and an output circuit, by which a direct current is generated to magnetize the electromagnetic chuck, or a pair of positive and negative phase pulses with a gradually increased frequency is generated to quickly demagnetize the electromagnetic chuck.

Abstract: The present invention relates to an arrangement for reduction of magnetic alternating fields for example in a vehicle or similar which comprises at least one electrical system which comprises at least two elements of which at least one comprises one or more components generating and/or consuming electricity, and which are connected through at least one connecting cable in which flows a current having an alternating current component generating a low frequency magnetic field. The arrangement also comprises at least one detecting element which is arranged to detect the alternating current component, and means for generating a compensating current with the use thereof. The compensating current flows adjacent to the connecting cable in such a way that the low frequency magnetic field is reduced or eliminated.

Abstract: A means for winding orthogonal coil systems that almost completely encompass and closely conform to magnetic media having a circular cylindrical form and orientation, including such media further encased in square or rectangular cassettes, cartridges or disk drives, while providing necessary access to that volume without the use of drawers and separable connectors or flexible lead wires for connection of the coils to energy stored in capacitors. The invention further employs hard wired circuitry for controlling the phase of currents in the coils and maintaining the desired rotation of the magnetic field. While this invention can be realized to degauss media inserted and extracted through the same side of the winding system, it is equally configurable to conveyance of media in one end of an orthogonal coil system and out of the opposing end.

Abstract: A bulk degaussing system automatically adjusts the operating voltage of the system to achieve a predetermined level of magnetic filed strength. A microprocessor is used to monitor the transient response of the system to maintain operation at a predetermined level of stored energy or to detect impending failure.

Abstract: A demagnetizing circuit and a current limiting device for being built into a power supply circuit of a color television receiver or color monitor display or the like with which it is possible to effect a reliable demagnetizing operation using existing components and without using either a positive characteristic thermistor which reaches a high temperature or a relay circuit. The demagnetizing circuit is connected in parallel with a power supply circuit having a smoothing capacitor and a negative temperature characteristic thermistor or fixed resistance for suppressing surge currents to the smoothing capacitor. It has a thermally actuated switch connected in series with one end of a demagnetizing coil by way of a positive temperature characteristic thermistor which is actuated by heat produced by the temperature negative characteristic thermistor or fixed resistance to cut off a demagnetizing current.

Abstract: In a method of testing a color cathode ray tube, an electron gun assembly is energized to emit electron beams and only a horizontal deflection magnetic field is applied to the electron beams so that a line image is displayed on a screen. A degaussing coil is located in front of the panel and a degaussing magnetic field having a frequency the same as that of a commercial power source. Thereafter, the degaussing coil is moved in a direction away from the panel and is deenergized when the coil is removed from the panel at a predetermined distance. A vertical deflecting coil is energized to display an image and a picture quality of the tube is tested.

Abstract: An automotive internal combustion engine demagnetizer that can improve engine performance by reducing the magnetic drag associated with the operation of the engine. By demagnetizing the engine block while the engine is running contributes to improved efficiency and performance. The demagnetizer is designed to be retrofitted onto a standard automobile having a conventional engine. A high current short duration repetitive rectangular pulse passing through the engine block serves to demagnetize it. It also allows metal particles both large and micro in size to stick to the engine block and other moving parts. This collection of particles contributes to engine failure and to the ultimate life of the engine. When the engine is not running, the present invention eliminates or reduces all magnetism in the engine block, causing almost all metal particles to fall into the crankcase that contains the oil. When the oil is drained, these particles are removed and discarded with the oil.

Abstract: A demagnetizing circuit has a positive characteristic thermistor and a demagnetizing coil connected in series with an alternating current power supply and is so constructed that it is possible to suppress the production of a low-frequency electromagnetic field. After the completion of a demagnetizing operation, the demagnetizing coil and the alternating current power supply can be completely isolated from each other, i.e. both ends of the demagnetizing coil can be electrically cut off from the alternating current power supply, so that it is impossible for residual demagnetizing current from the alternating current power supply to produce a low-frequency electromagnetic field in the demagnetizing coil. Also, preferably, at least one end of the demagnetizing coil is kept at a reference potential by way of a capacitor to dissipate any currents which may be induced in the demagnetizing coil by any influence other than the alternating current power supply.

Abstract: In one example of a demagnetization (degaussing) circuit, main electrodes of a TRIAC, a first positive temperature characteristic thermistor and a demagnetization coil are connected in series to both ends of an AC supply, and a heat-sensitive switch and a heating resistor are connected in series between an end of the TRIAC on the side of the AC supply and an end of the demagnetization coil on the side of the AC supply. A connecting point between the heat-sensitive switch and the heating resistor is connected to a gate electrode of the TRIAC, and the heat-sensitive switch and the heating resistor are thermally coupled to each other. The disclosed demagnetization circuit does not need a secondary electric circuit such as a relay control circuit and allows easy substrate design, with a small number of components and at low cost.

Abstract: A magnetic field shielding device of a CRT (cathode ray tube) display includes a degaussing coil for preventing a magnetic field, generated by a voltage supplied to a deflection coil of the display, from being emitted from the display. A tilt coil maybe disposed at the middle portion of the degaussing coil so as to surround an electron gun of the cathode ray tube. The top and bottom portions of the degaussing coil are arranged so as to be horizontal. Both sides of the middle portion of the degaussing coil are bent inward so as to approach to each other, and so as to have a predetermined distance therebetween. The shielding device prevents dark color purity from being generated at the lower portion of the display.

Abstract: A bulk degaussing system for bulk erasure of various magnetic media includes a source of magnetic flux for generating a magnetic field with a predetermined field strength within a predetermined volume defining a predetermined degaussing window, a transport system for transporting the magnetic media relative to the degaussing window such that every point on the magnetic media is exposed to the magnetic field. A control circuit is included which modulates the magnetic field to reduce power consumption. In addition to reducing power consumption, the modulated magnetic field minimizes system performance degradation due to stalls of the magnetic media transport system due to interactions between the magnetic field and ferromagnetic components associated with certain magnetic media.

Abstract: A demagnetization circuit controls a demagnetization current to its demagnetization coil by means of a PTC thermistor with positive characteristic. The PTC thermistor is connected in series with and thermally coupled to a heat-sensitive switch. An NTC thermistor with negative characteristic for suppressing rush current of the voltage source is also thermally coupled to the heat-sensitive switch. After a power switch is closed, the heat-sensitive switch is opened by the heat emitted from the PTC thermistor and remains open by the heat from the NTC thermistor. The two thermistors and the heat-sensitive switch are contained in a case for easy handling and to make the component compact.

Abstract: A device for scrambling the information held by magnetic memory storage media and rendering the information inaccessible. The portable device provides a passage through which a magnetic memory storage medium, also known as a diskette, passes in such proximity to magnetic material so that the magnetically sensitive components of the memory storage medium are thereby disordered by the force of the magnetic field emanating from the magnetic material.

Abstract: The magnetic states of MR reproducing heads are reinitialized during media drive manufacturing by applying initializing magnetic fields to the transducers after they have been manufactured and incorporated into media drive assemblies.

Abstract: To degauss cassettes of magnetic tape, a magnetic field is applied to the magnetic material while the magnetic material moves with respect to the field in a single air gap of a flux density of at least 1,000 gauss and at an angle between 20 degrees and 70 degrees from the horizontal of the magnetic tape for a time priod of at least one second and the field is alternated at a frequency of at least ten hertz. The magnetic material may be rotated while it is in the field.

Abstract: A linear permanent magnet position sensor is produced by a novel permanent magnet demagnetization process. Demagnetization field strength is controlled to demagnetize a thinner portion of the permanent magnet less than, equally, or greater than a thicker portion of the same permanent magnet. Linearity and stability are both tailored through a single demagnetization step.

Abstract: A degaussing circuit comprising a rectifying circuit for rectifying an AC voltage inputted therein into a DC voltage, a capacitor for smoothing the DC voltage from the rectifying circuit, a RC charging circuit for charging with the DC voltage smoothed by the capacitor, a positive temperature coefficient resistor having a resistance which is increased with an increase in a temperature due to an AC current flowing therethrough upon power supply, a degaussing coil for removing a magnetic field in response to the AC current flowing through the positive temperature coefficient resistor thereto, a relay for controlling the flow of the AC current through the positive temperature coefficient resistor to the degaussing coil, and a relay driving circuit for controlling an ON/OFF state of the relay in response to the voltage charged on the RC charging circuit.

Abstract: A deactivator for deactivating electronic article surveillance tags includes a deactivating coil, drive circuitry controllable for supplying driving signals to the deactivating coil, a reference signal generator for generating a reference signal having preselected characteristics varying with time, a comparator for comparing characteristics of the driving signals with the reference signal characteristics, and a control unit for controlling the drive circuitry in accordance with signal comparisons effected by the comparator.

Abstract: This method produces a tape having a plurality of recorded segments separated by cue tones and having a reduced tendency to generate false cue tones. The method includes applying a layer of a liquid dispersion to a nonmagnetic substrate. The method also includes the steps of orienting the pigment by applying a magnetic field, solidifying the layer of liquid dispersion on the substrate, and applying a demagnetizing field to the layer to neutralize the remanent magnetization.

Abstract: A degaussing circuit has a degaussing coil, an oscillator, amplifiers, a bias source, a capacitor, a switch and a time period controller. The oscillator supplies high frequency alternating currents which are amplified by the amplifiers to drive the degaussing coil. The bias source and capacitor activate the amplifiers. The capacitor applies a gradually reducing bias to the amplifiers. The switch controls the charging and discharging of the capacitor and thus causes the application of the gradual reducing bias to the amplifiers. The time period controller regulates the operation period of the switch and, therefore, the charge and discharge of the capacitor.