GB440451A - Improvements in or relating to thermionic amplifiers - Google Patents

Abstract

440,451. Valve amplifying circuits. KRAWINKEL, G., Bothstrasse, Lichterfelde, Berlin. Oct. 25, 1934, No. 30621. Convention date, Oct. 25, 1933. [Classes 39 (i) and 40 (v)] A direct-current amplifier comprises two branches having equal gain, one of which produces one more phase reversal than the other and the two branches are fed in push-pull, the outputs being fed to a common circuit in which are balanced out fluctuations in the supply voltages or electron sources which act equally in the same phase on the two branches. In all the embodiments described the valves of each branch are resistance coupled and are one greater in number in the lower branch than the upper. In one embodiment, Fig. 2, each pair of valves has a separate grid and anode battery while the grid of the extra valve in the lower branch is maintained at the correct potential by the inclusion of a resistance r<1> in its grid circuit carrying current from a source E through the resistance r<2> and the anode resistance ra<1> of the preceding valve. The resistance Ra constitutes the common anode resistance for the end valves of both branches the output of the amplifier being derived from the terminals e, f connected thereacross. Neutralizing condensers k are connected in each case between the anode of a valve and the grid of the preceding stage, while a reaction condenser C is connected between the grids of valves in the two branches which are in phase and the resistanee r<1> is bridged by a condenser K. The anode and grid sources of potential may be replaced by a current carrying potential divider. In other embodiments, Figs. 3 and 4 (not shown), the valve cathodes are at a common potential, a common anode source is provided and the grids are all maintained at the appropriate potential by resistances carrying current from a common source. A circuit for giving a push-pull output, Fig. 5, comprises two such systems, the first of which comprises the branches having valves R1, R2 and R1<1>, R2<1>, R3<1> respectively, while the branches of the second system comprise valves R1, R3, R4 and R1<1>, R2<11>. The first system produces an output across the terminals c, d which is out of phase with that across e, d produced by the second system. In order to eliminate the Sehrot effect from the earlier stages of the amplifier, the corresponding valves in the two branches are arranged with a common electron source such as the cathode H, Fig. 6, common to the two triode systems H, G1, A1 and H, G2, A2. Another double triode valve for the same purpose comprises an electron source H, Fig. 7, an accelerating electrode a with an opening through which electrons pass to be spread into a space charge cloud by a retarding grid BG which feeds the triode systems G1, A1 and G2, A2. To prevent the return of electrons to the electrode a suitable insulation may be provided.