GB499546A - Improved thermionic-valve circuit for generating ultra-high frequency oscillations - Google Patents

Abstract

499,546. Valve generating circuits. NAAMLOOZE VENNOOTSCHAP PHILIPS' GLOEILAMPENFABRIEKEN. March 5, 1938, No. 6986. Convention date, March 8, 1937. [Class 40 (v)] In a short-wave oscillator in which variations in the supply voltage affect the frequency generated by varying the grid-cathode capacity in parallel with the tuned circuit, the effects of corresponding changes in positive-electrode and heating voltages are in opposite directions but those on the positive electrode normally preponderate. According to the invention, the fluctuations in the voltage on the positive electrode nearest to the control grid are reduced, so that the effect of these fluctuations is substantially compensated by the fluctuations in the heating voltage, by deriving the voltage on the said electrode from a potentiometer connected across the supply mains in series with a resistance the value of which depends on the applied current or voltage. As shown, the anode of a triode is supplied from a potentiometer 13 in series with a resistance 14 having a high negative temperaturecoefficient of resistance so that its resistance falls with increased voltage across terminals 11, 12 and the fraction of this voltage which is applied to the anode is decreased. In another arrangement, Fig. 2 (not shown), the potentiometer slider is connected to the screen grid of a pentode oscillator, and the elements 13, 14 are interchanged the latter however having a high positive temperature coefficient. As applied to the local oscillator of a superheterodyne receiver, Fig. 3 (not shown), the potentiometer slider is connected to the oscillator anode and to the screen grids of a frequency-changing octode.