674 
- 35 = 
could be eliminated by the use of a thyratron in the input. When the timing 
condensers or wiring thereto show appreciable leakage, the linearity is 
affected. The beam-brightening circuit is direct-coupled and is likely to 
drift under extreme conditions of heat, humidity, or tube and resistor drift. 
Finally, the regulated supplies require wire-wound resistors in the ampli- 
fier-tube grid circuits to assure voltage stability. 
In operation this design has given very good service, The linearity, 
in terms of time-displacement ratio, is better than 1 percent and is con- 
stant over a period of time which is long compared to the time required for 
a single measurement. The range in speeds is from 0.5 msec to 50 msec for a 
yin. trace on a DuMont type 208 oscillograph, 
(b) Time delay and beam brightener, -— This unit fills a double func- 
tion. Upon the reception of a tripping signal, it produces one pulse at a 
variable time later, and then a second pulse at a variable time after the 
first pulse. The other function of the unit is to provide a variable time 
delay after the tripping signal and then produce a beam=brightening signal 
of variable duration. 
The description of the operation may be followed by reference to Fig. 
17 The tripping signal is fed into the first thyratron through a cathode 
follower to remove the effect of thyratron-grid current upon the tripping 
circuit. The required tripping signal may be varied from +0.3 to +7 volts 
by adjusting the thyratron-grid bias. The heart of the time-delay system 
is the next circuit. When the first thyratron fires, it changes the next 
tube from full conduction to full cutoff. The timing condenser C proceeds 
to charge toward the potential of the positive supply, and when it reaches 
-3 volts the second thyratron fires, The starting voltage for this charging 
process is substantially independent of tube constants because of the large 
plate resistor (5 megohms), and the charging action takes place with the 
tube cut off. With regulated supply voltages, the time to fire the second 
thyratron is determined only by the resistance and capacitance. When this 
action is over, the same process is repeated in the second delay circuit. A 
neon glow lamp indicates when this process has taken place. A manual reset 
button prepares the circuit for the next operation by cutting off the thyra- 
tron supply voltage. 
