GB256653A - - Google Patents

Abstract

256,653. Soc. Franþaise Radio Electrique. Aug. 10, 1925, [Convention date]. Thermionic generators.-With the object of reducing the effect of parasitic capacities on the tuning and the losses in thermionic oscillation generators, the oscillatory circuit 6, 7, Fig. 1, is connected at three points to the plate, grid, and filament of the valve 3, and the earth connection 11 is made at a suitably-chosen point 11. The filament source 2 is earthed and supplies the filament through a choke 10 and a portion of the coil 7, and the high-tension source 1 is connected to the plate through a choke 4. A condenser S is interposed between the plate and the oscillatory circuit 6, 7 and a grid leak and condenser 8 in the grid connection. In a modification, Fig. 4, for generating short waves, a symmetrical pair of valves 3, preferably with water-cooled anodes, has the two anodes connected to each other and to the positive side of the supply 1, the negative side being earthed. The anodes thus carry no high-frequency potential. Four coils 7 have their outer ends connected in pairs through grid leaks and shunting-condensers 8 to the respective grids of the two valves 3. The pairs of coils are connected to each other at their inner ends, the junction points being respectively connected to the negative side of the anode supply 1, and to the filament supply 2. The ends of each filament are connected to taps on the coils 7, so that the filament current flows through portions of the coils. The frequency of the oscillations may be determined by the self-capacities of the coils, and the valve electrodes and leads, or may be determined by added capacity 6 or inductance 7a. The Specification as open to inspection under Sect. 91 (3) (a) also comprises various modifications in oscillation generators and amplifiers of the kind in which an oscillatory circuit is connected at three points to the electrodes of a valve. As shown in Fig. 4 (Cancelled), the plate current is supplied from a source 1 through a choke 4. The plate blocking-condenser 5 is connected to a variable tapping on the choke 4, to enable the power to be regulated. A variometer may be used instead of the tapped choke coil. The filament circuit may comprise one or more chokes 10, 10<1>, earth connections being made at one end 9 of the filament battery 2, and at an adjustable point 11 of the coil 7 in the oscillatory circuit. This enables either the plate or the filament to be maintained at earth potential so far as high-frequency is concerned. An intermediate adjustment of the tap 11 can be found, at which the effect on the tuning and on the losses of the parasitic capacities to earth of the plate and filament is a minimum. The coil 7 may overhang beyond the connection of the tuning-condenser 6. as shown in Fig. 5 (Cancelled), and the extended portion may be tapped at 15. 16 for variable connection to the grid circuit and to the aerial circuit respectively. Reaction voltages are thus taken partly from the aerial circuit and partly from the oscillatory circuit 6, 7, giving greater efficiency and stability of frequency. Thermionic modulating systems.-Fig. '7 (Cancelled) shows a generating-set for modulated transmission, with means for preventing the modulation from affecting the frequency. The plate voltage of the oscillator 4 is supplied by an alternator 2, which may have a direct current source 1 in series with it. A transformer 12 fed' from the alternator 2 applies voltages of suitable amplitude and phase to the transformer 10 in the grid circuit of the oscillator 4. Alternatively, the transformer 12 may ,apply voltages in the oscillatory circuit 7, 8 through a transformer 11 the core of which is saturated by direct current from a battery 16. Fig. 6 (Cancelled) shows a generator 3 and modulator 5 adapted to produce either acoustically-modulated waves for telegraphy, or speech-modulated waves for telephony. A transformer primary coil 6 is connected in the common plate supply circuit of the two valves, and the grid of the valve 5 is connected by a switch 12 either to the microphone transformer 9 (for telephony), or through a shunted grid leak 8 to a tuned secondary coil 7 of the transformer 6 (for telegraphy). In the latter position, the valve 5 generates current of acoustic frequency, which modulates the output of the oscillation generator 3. This subject-matter does not appear in the Specification as accepted.