GB304382A - Improvements in and relating to transmitting apparatus for wireless telegraphy - Google Patents

Abstract

304,382. Im Thurn, J. K., Shearing. G., and Matthews, C. Oct. 24, 1927. Thermionic amplifiers. - A cascade amplifier comprising a number of double-acting or pushpull stages I - - V1 of the type described in Specification 149,018 controlled by a piezo-crystal Q connected symmetrically between the two grids of the first stage is characterized by the provision of coupling coils L2 in the oscillatory circuit. Provision is made for maintaining the supply voltages at constant value during the marking and spacing periods, keying being effected in the manner described in Specification 203,788. The grid coils L2 have low self-inductance and mutual coupling to the plate coils L1, so that the generated oscillations conform to the fundamental crystal frequency, or to an odd harmonic. The circuit L3, C3 is tuned to the selected frequency. Balancing condensers N1, N2 &c. normally stabilize the system. Grid-biasing potential, derived from the rectifiers U1, U2, paralyze the valves V9, V10 when the key R is in the spacing position S. Simultaneously auxiliary valves V13, V14 absorb the current diverted from the high-tension supply. The valves V11, V12 are designed to allow static current to pass, so that the anode rate of dissipation remains constant. Rectified plate current is supplied through a suitable smoothing-system from an AC source; or alternatively the initial stages may be supplied with direct current, and later stages supplied from an alternating-current source. Instead of being crystal-controlled, any of the stages following the first may be made self-oscillatory. For instance, as shown in Fig. 3, a switch S may disconnect the stabilizing condensers N7. N8 and connect the grids of V9, V10 across an inductance G, so as to maintain oscillations through that inductance and the grid-anode capacities of the valves. The output from the last valve is coupled to the aerial L14 through small condensers C12 and an intermediate circuit L13, C13, the centre point of which may be earthed. The intermediate circuit and the aerial coils may be screened from the output circuit of the valve amplifier.