668 ape 
The circuit employed is basically a degenerative stabilizer with ampli- 
fied control voltage applied to the type 807 series tube. The amplifier is 
a so-called "cascode" eireuat ee consisting of tubes 6J5, Nos, 2 and 3, con- 
trolled by output-circuit variations coupled to their erids by the dividers 
in the plate circuit of the constant-current tube 6J5 Noe 1 (see Sece 3). 
Reference voltages for this tube and the cascode are supplied by the gas 
regulator tubes VR105 and VR150. The interlock connection in the power cir- 
cuit is intended for connection with other equipment to prevent premature 
application of voltage. The lining up and operation of the circuit are 
straightforward and require no comment. 
The output voltage changes less than 2 volts when the a-c line is varied 
from 90 to 125 volts and the peak-to-peak ripple in the output is less than 
0.5 volts. The internal impedance of the supply is less than 500 ohms. 
(c) Intensity-modulation coupling circuits. -- The requirements for 
cathode=-ray tube be2m modulation are: (i), a means of applying a positive 
voltage of 20 to 100 volts to the grid of the tube for intervals of from a 
few milliseconds to seconds, the d-c level of the grid being 1000 volts or 
more below ground potential; (ii), freedom from 60-cycle or other pickup. 
Two simple coupling methods can be employed successfully -- condenser 
coupling to the grid,or applying amuch larger brightener voltage to the top 
of a potentiometer circuit on which the grid is tapped. The first is the 
most easily constructed circuit of all, but suffers from two disadvantages. 
First, the time constant of the grid circuit must be much greater than the 
time the beam is to remain on if the intensity is to remain essentially con- 
stant. If this duration is longer than, say, 100 msec a condenser of high 
capacity and voltage rating is required and some time must be allowed between 
brightening cycles to permit the circuit to recover. 
A second drawback to use of candenser coupling is that the condenser 
effectively connects the cathode-ray tube grid to the brightener as far as 
fluctuations or ripple is concerned, while the cathode follows accelerating 
voltage-supply variations, The result is that any ripple in this supply 
appears as an undesired intensity modulation. Though the effect is not 
always serious and a good high-voltage supply will eliminate it, it is a 
basic difficulty. 
/ , ; 
fant and Hickman, Rev. Sci, Inst. 10, 6 (1939). 
