GB580891A - Improvements in and relating to time base generators for cathode ray tubes - Google Patents

Abstract

580,891. Saw-tooth generating circuits. DEBSKI, J. M. June 28, 1944, No. 12251. [Class 40 (v)] In a saw-tooth time base generator, in which a rectangular pulse is applied to a valve having a condenser connected between anode and control grid to produce the saw-tooth output, a modifying potential is applied to one or more electrodes to modify the generator output. The modifying potential may be applied to the control and/or screen grid and may expand or contract the time base. The anode current of Miller time base valve V is normally zero due to bias on the suppressor grid, but upon a positive square wave being applied over coupling condenser C1, the suppressor grid rises to earth potential, allowing anode current to flow and the anode potential to fall linearly as condenser C discharges to generate the time base voltage. Upon an additional positive pulse being applied over coupling condenser C2 and variable resistance R2 to resistance R3, diode V1 conducts, increasing the rate at which the grid potential of valve V rises and hence the rate of discharge of condenser C. At the cessation of the additional pulse, the condenser C discharges at the previous rate. In a modification, Fig..4 (not shown), the additional pulse is also applied to the screen grid and may be negative to contract the time base. A tetrode operating with low screen voltage may be used in place of the pentode, the main pulse raising the screen potential to an operating value. A variable delay network may be inserted between the pulse generator and the valve V to allow adjustment of the commencement of the expanded portion of the time base.