In particular in grid - base - circuit operating roehre

摘要

1,080,356. Thermionic valves. TELEFUNKEN PATENTVERWERTUNGS G.m.b.H. Aug. 17, 1964 [Aug. 23, 1963], No. 33453/64. Heading H1D. In a circuit arrangement for amplifying or generating U.H.F. signals including a thermionic valve having an indirectly-heated cathode, the construction of the cathode and heater is so arranged, or components are provided, so that the cathode-heater resonances of the valve lie outside the working frequency band of the arrangement. The cathode-heater resonances may be shifted above the working frequency band by use of a short, thick heating element with heavy gauge supply leads to reduce the inductance of the heater circuit, and by use of a short cathode, e.g. having a diameter greater than its length, and multiple, thick, low inductance cathode supply leads. Alternatively, a helical heater may be embedded in a high dielectric material spaced from the cathode to increase the capacity between adjacent turns of the heater, or the space between the cathode and heater may be filled with a low dielectric material to reduce the heater-cathode capacity. A dielectric material may be provided between the ends of the heater and the cathode tube to produce a capacitive susceptance which may be compensated by a corresponding input circuit, or separate condensers may be inserted between the ends of the heater and the cathode tube. The cathode-heater resonances may also be shifted below the working frequency band, the arrangement then being such that the cathode to grid series resonance lies above the working frequency band.