Abstract: The present invention concerns a grid amplifier tube producing with an approximately constant gain at least a combination of a first signal for a short duration and a second signal for a longer duration. The maximum voltage of the first signal is higher than the maximum voltage of the second signal. To improve the efficiency of the tube, the anode polarization voltage is adjusted to a level enabling the tube to operate as a class B, AB or C amplifier and to produce the maximum voltage of the second signal but not the maximum voltage of the first signal. The class of the amplifier is made to vary towards class A for the duration of the first signal so that it produces the maximum voltage of the first signal. For this purpose at least one of the polarization voltages of the electrodes of the tube is made to vary. The present invention finds particular application to television transmitters operating in negative transmission systems.

Abstract: The means providing capacitive decoupling between the inside cylinder and a grid electrode are disposed at about one fourth of the wavelength of the highest operating frequency from the tube end of the inside cylinder. This is a current node, and dielectric losses at the highest frequency are thus greatly reduced. The match is less good at lower frequencies, but the corresponding dielectric losses are much less at lower frequencies. The first piston provides capacitive coupling between the first and second cavities whereby the entire outside cylinder may be maintained at ground potential.

Abstract: A frequency band filter includes a plurality of coupled elementary resonator cavities defined by pistons disposed within a coaxial line. The position of the pistons along the line is adjustable thereby providing selectable tuning.