GB423961A - Improved single tube modulated oscillator - Google Patents

Abstract

423,961. Valve generating circuits. BROWN, W. F., 29, Bell Street, Brierley Hill, Staffordshire. Oct. 27, 1933, Nos. 29826 and 32425. [Class 40 (v)] A single-valve oscillator primarily intended for testing, demonstrating, or servicing wireless receivers comprises a tetrode valve 1 preferably of the screen grid type, connected as a dynatron by biassing its screen grid to a higher positive potential than the anode. The oscillatory circuit 15, 16, 13 in the anode circuit is switched at 17 for three wave ranges. Modulation may be applied to the control grid circuit from a source 32 such as a gramophone pick-up through a transformer 27 and potentiometer 28. Alternatively self-modulation may take place with the switch 34 on contact 44 thus back-coupling the screen grid to the control-grid circuit through condenser 43 resistance 40 and inductance 41. Constant amplitude is obtained by feeding back oscillations across condenser 24 to a unilateral conductor 25 ; the rectified oscillations vary the control grid bias in such sense as to keep the oscillation amplitude constant. Condenser 30 is inserted by switch 31 only for self modulation. Resistance 4 provides normal control grid bias, from a tapping on which the output from the oscillator is taken through resistance 38 and condenser 37 to the receiver through a shielding tube. Where the supply current is obtained from batteries the radio frequency output is taken from a voltage divider comprising a condenser and high resistance connected between anode and earth. Specification 400,995 is referred to.