Patent GB-508124-A (GB)
Title: Improvements in time bases for cathode ray oscillographs
IPC: G01R13/22
Filed: 1938-03-30
Abstract: 508,124. Cathode-ray oscillographs valve generating circuits. MULLARD RADIO VALVE CO., Ltd., and RUSSELL. A. W. March 30, 1938, No. 9750. [Class 37] [Also in Group XL] A time-base for a cathode-ray oscillograph comprises a condenser which is alternately charged from a D.C. source and discharged by a gas-filled triode or equivalent device, means being provided for automatically controlling the charging current of the condenser in accordance with the recurrence frequency of the waveform to be examined. A condenser C1 is charged through a pentode V4 or other constant-current charging valve, the charging current being varied by controlling the potential applied to the screen grid. Discharge is effected by means of a gas-filled triode V5. A switch S enables condensers C2, C3 of different values to be substituted for the condenser Cl. The cathode-ray tube is fed from terminals 01, 02 connected to the tapping point and earthed end of a potentiometer resistance R11 connected at its upper end to the anode of the valve V4 through a condenser C9. The anode of the pentode V4 is also connected to the cathode of the triode V5 through a resistance R12. The waveform under examination is applied by means of terminals 11, 12 to a potentiometer resistance R1, the tapping point of which is connected through a condenser C7 and resistance R2 to the control grid of a pentode VI. The anode circuit of this valve includes an inductance L, the reactance of which is small compared with the internal impedance of the valve V1, and a de-coupling resistance R3. The lower end of the inductance L is connected to the anode of a diode V2 and also to the grid of a triode V3. The cathodes of the valves V2, V3, V4 are connected to the lower end of a resistance R17 in a chain of resistances R15, R16, R17, R18 across the H.T. supply. The anode of the valve V3 is connected to the screen grid of the pentode V4 by a resistance R10. The voltage across the inductance L increases linearly with the frequency and is rectified by the valve V2 and applied to the grid of the valve V3. which becomes more negative with increase of frequency., The screen grid of the pentode V4 then becomes more positive and increases the charging current of the condenser C1. The operation of the valve V5 is timed by grid control effected by valves V6, V7. The grid' of the valve V5 is connected through resistances R13, R14 to a variable tapping on the resistance R16. The junction of the resistances R13, R14 is connected through a condenser C10 to the anode of the valve V6. This valve is controlled through resistances R21, R22 and condenser C13 from the anode of the valve V7, the grid of which is connected to the tapping of the potentiometer R1. If large variations of amplitude occur in the waveform under examination, the amplitude may be controlled by connecting the anode of the valve V7 through a condenser C14 to the anode of a diode rectifier V8 which is also connected to a tapped load resistance R24. The tapping is connected to a smoothing circuit R23, C12, the smoothed voltage being fed through resistances R4, R2 to the control grid of the pentode V1.