GB766168A - Improvements in or relating to electric amplifier circuits employing gas discharge tubes - Google Patents

Abstract

766,168. Valve amplifying circuits. PHILIPS ELECTRICAL INDUSTRIES, Ltd. July 30, 1954 [Aug. 4, 1953], No. 22317/54. Class 40(6) In a power amplifier employing a plasmatron, i.e. a gas-filled electron discharge tube comprising an anode 7, a cathode 6, a further heated auxiliary cathode 4 providing an electron stream whereby the gas in the space between the anode and first-mentioned cathode is ionized and means for controlling the electron stream and thus controlling the ionization and hence the anode-current flow in the discharge tube, the accelerating voltage applied between the two cathodes in order produce the ionizing electron stream is derived from a high frequency oscillatory source which is coupled to the valve through a step-up transformer and is modulated by the low-frequency signal to be reproduced in the output circuit of the amplifier. It is stated that an accelerating voltage of at least 60 volts is required; such a direct voltage may not be readily available in certain applications, whereas a high voltage oscillatory voltage may be derived by the use of a transformer. In a first embodiment, Fig. 2, an oscillator 13 provides an oscillatory voltage which is rectified and smoothed before being applied to the main cathode 6 of the plasmatron. Due to the application of this voltage electrons from the auxiliary heated cathode 4 which is partially surrounded by a screen 5 connected thereto, are accelerated into the space between the cathode 6 and anode 7 where they ionize the gas and allow current to be drawn from the battery 9 through the loudspeaker 8. The ionization is dependent upon the density of the electron stream; this is controlled by the application of the voltage to be amplified to the terminals 1 to control the amplitude of the oscillations generated by the valve 13 and thus the amplitude of the. accelerating voltage applied to the plasmatron. In Fig. 3 the output of a final I.F. amplifier supplies the accelerating voltage to the plastmatron through a transformer coupling and a rectifier 17. The rectifier 17 may be replaced by a capacitor which may, if necessary, have a resistor connected in parallel (Fig. 4, not shown), or by a parallel arrangement of a capacitor'and a capacitor and resistor in series (Fig. 5, not shown). In these arrangements, the rectifying action of the plastmatron itself provides the accelerating voltage. Specification 435,785 [Group XL] is referred to.