US1906246A - Apparatus embodying electric discharge lamps - Google Patents

Description

May 2, 1933.

c. o. BROWNE APPARATUS EMBODYING ELECTRIC DISCHARGE LAMPS Filed Oct. 23, 1929 Patented May. 2, 1933' UNITED STATES PATENT OFFICE CECIL OSWALD BaowNE, or EALING common, noimon, ENGL ND, AssIeNoR. IBY MESNE ASSIGNMENTS, 'ro RADIQCORPORATION or AMERICA, or NEW YORK, N. Y.,

A CORPORATION OF. DELAWARE APPARATUS, monrme ELECTRIC DISCHARGE LAMPS Application filed October 23, 1929, Serial No. 401,931, and in Great Britain November 26, 1928.

The present invention relates to apparatus embodying electric discharge lamps, such as glow or are discharge lamps, in which the intensity of the light emitted by'the lamp is y varied in accordance with electric oscillations.

Where a mercury vapour discharge lamp is used as a lightsource in photographic sound recording, a steady voltage is impressed on the lamp in order to light it and electrical oscillations corresponding to the sounds to be recorded are superposed upon the steady voltage and serve to vary the light emitted in aceordance with the sound.

It will be clear that the superposed oscillations will produce oscillatory changes in the steady voltage and cause it to vary between maximum and minimum values which are equally above and below the steady voltage respectively. Since there is a critical voltage (known as the cut-off voltage) below which the lamp does not remain alight it will be clear that if the minimum value of the voltage is, with normal sounds, close to the critical voltage, an abnormally loud sound will cause extinction of the lamp with consequent distortion of the recorded sound waves.

According to the present invention there is provided apparatus comprising an electric discharge lamp the steady illumination of 0 which is adapted to be varied in accordance with electrical oscillations or variations, wherein there is associated with the oscillatory or variable current circuit a current limiting device adapted to prevent or to minimize the risk of the voltage across said lamp falling below the cut-off value upon increase in the amplitude of said electrical oscillations or variations. i

The invention is illustrated in the accompanying drawing in which Figs. 1 and 3 are diagrams of two difierent circuits in accordance with the invention, and Figs. 2 and 4 are diagrams illustrating the working of the circuits in Figs. 1 and 3 respectively.

Referring to Fig. 1, electrical oscillations, for example from a microphone, are applied to the terminals 2 and are thus impressed upon the grid circuit of the valve 3. This valve 59 may be the last valve of a multi-stage amplifier. The anode circuit of the valve 3 con-- tains the primary winding of a transformer 4. The secondary winding of the trans former 4 is connected to a discharge tube 5, a stabilizing resistance 6 and a battery 7 arranged in series. The battery 7 provides the current for the steady illumination-of the discharge tube 5. Grid bias for the valve 3 is supplied through a grid leak 8 and is furnished by battery 9 shunted by a potential divider 10. The resistance 10 and the battery 9 are shunted by a by-pass condenser 11.

The grid bias upon the valve3 is adjusted by means of the potential divider 10 so that the valve3 tends to overload or rectify on the negative half swing when the voltage swing upon the grid circuit of the valve exceeds a value which is suflicient to reduce the potential diflerence across the discharge tube 5 to the cut-off value or slightly above this. This isillustrated in Fig. 2 in which, in curve 12, the anode current i, of the valve 3 is plotted against the grid voltage V,;. The anode current will, for the purpose of this specification be regarded as proportional to the potential difference across the primary winding of thetransformer 4. The anode current corresponding to the minimum value of grid voltage V is that which represents a potential difference across the discharge tube 5 in opposition to that produced by the battery 7 or the operating potential for the lamp and having a magnitude less than that produced by the battery 7 by an amount equal to or rather greater than the cut-01f voltage of the tube 5.

The grid bias is therefore adjusted to the value v and the grid swing is then represented by the curve 13. The value of the potential differences applied to theterminals 2 is such that normally it does not exceed the value given by the .curve 13. That is to say, when the potential differences correspond to sounds, 4 the potential differences shown in curve 13 correspond to the loudest sounds with which it is expected to have to deal. If, through any unforeseen circumstances, the volume exceeds this value, it will be seen from curve 12 that the valve 3 willact as a rectifying 100 or overloaded current limiter in the region of V, to prevent extinction of the tube 5.

Referring to Fig. 3, the modulating oscillations are fed to terminals 2 which are connected to the primary winding of a transformer 14. The secondary winding of the transformer 14 is connected to a resistance 15, a diode rectifier 16, a discharge tube 5 and a battery 17 all arranged in series. The steady illumination of the tube 5 is provided by battery 7 through a stabilizing resistance 6 and a choke 18 which prevents the circulation of oscillatory currents in the circuit 7, 6, 18.

The voltage of battery 17 is so adjusted that the diode 16 commences to rectify when the electromotive forces in the modulating circuit exceed a certain predetermined value which causes the potential difference across the tube 5 to fall, on one half swing, to a value equal to or slightly greater than the cut-off voltage.

This is illustrated in Fig. 4 in which the curve 19 shows the relation between the current 2'. in the diode 16 and the voltage V, across it. So long as the diode is operating to the right of the ordinate i. there will be no rectification but if the voltage swing across the diode is greater than that shown in curve 20 (assuming that the voltage swing takes place about the centre line V the diode will rectify and thus prevent further decrease in the minimum potential difference across the discharge tube 5, this potential difierence being slightly above the cut-off voltage of the tube 5.

The resistance 15 assists in preserving a linear relation between V, and i. in the diode 16 and so reduces distortion.

I claim:

1. In an electrical apparatus, the combination of an electric discharge lamp having a predetermined minimum operating voltage, a source of electrical oscillations of varying voltage amplitude, means for applying said electrical oscillations to said lamp, a source of constant operating voltage for said lamp, said last named voltage being-at least equal to the maximum desired voltage amplitude of the applied electrical oscillations plus said minlmum operating voltage of the lamp, and means interposed in circuit between said source of electrical oscillations and said lamp for limiting the voltage amplitude of said oscillations applied to the lamp to a value not grgater than said maximum desired ampli- 2. In an electrical apparatus, the combination of an electric discharge lamp having a predetermined minimum operating voltage, a source of electrical oscillations of varying voltage amplitude, means for applying said electrical oscillations to said lamp, a source of constant operating voltage for said lamp, said last named voltage being at least equal to the maximum desired voltage amplitude of the applied electrical oscillations plus said minimum operating voltage of the lamp, means interposed in circuit between said source of electrical oscillations and said lamp for limiting the voltage amplitude of said oscillations applied to the lamp to a value below a predetermined value not exceeding the difference between the applied constant operating voltage and the mlnimum operating voltage, and means for adjusting said last named limiting means to respond to sald predetermined value.

3. In an electrical apparatus, the combination of an electric discharge lamp having a predetermined minimum operatin voltage, a source of electrical oscillations o varying voltage amplitude, means for applying said electrical oscillations to said lamp, a source of constant operating voltage for said lamp, said last named voltage being at least equal to the maximum desired voltage am litude of the applied electrical oscillations p us said minimum operating voltage of the lamp, and means including an electric valve interposedin circuit between said source of electrical oscillations and said lamp for limiting the voltage amplitude of said oscillations applied to the lamp, said 'means being adjustable whereby the anode current of said valve is reduced on each negative half wave substantially to zero in response to oscillations of said maximum desired amplitude.

4. In an electrical apparatus, the combination of an electric discharge lamp having a predetermined minimum operating voltage, a source of electrical oscillations of varyin voltage amplitude, means for applying sai electrical oscillations to said lamp, a source of constant operating voltage for said lamp, said last named voltage being at least equal to the maximum desired voltage amplitude of the applied electrical oscillations plus said minimum operating voltage of the lamp, and means interposed in circuit between said source of electrical oscillations and said lamp for limiting the voltage amplitude of said oscillations applied to the lamp, said means including a rectifier in series with said 1am and regulating means in circuit with said rectifier for preventing its operation in response to electrical oscillations below a predetermined permissible high amplitude.

5. In an electrical apparatus, the combination of an electric discharge lamp having a predetermined minimum operatin voltage, a source of electrical oscillations o varying voltage amplitude, means for applying said electrical oscillations to said lamp, 0. source of constant operating voltage for said lamp, said last named voltage being at least equal to the maximum desired voltage amplitude of the applied electrical oscillations, plus said minimum operating voltage of the lamp, a stabilizing impedance in circuit with said lamp and source of operating voltage, and ad ustable means including a biased electric valve inter osed in circuit between said source of electrical oscillations and said lamp for limiting the voltage amplitude of said oscillations applied to the lamp to a value not grgater than said maximum desired amplitu e.

In testimony whereof I have signed my name to this specification.

CECIL OSWALD BROWNE.

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