nee 669 
The divider, or potentiometer, method suffers from the disadvantage of 
being wasteful in that only a small fraction of the large positiv2 voltage 
which must be applied at the top of the divider is used. This places special 
requirements on the driving circuit, Also, some of the accelerating voltage 
must be wasted to provide bias for the tube. 
More satisfactory coupling circuits for brightening can be provided at 
the expense of added tubes and components. One fairly simple method is to 
use a constant-current tube, as shown in Fig, 14, The plate current of tube 
Tg can be made independent of its plate voltage by giving resistor R, the 
value pR5, where p is the amplification gaetor A signal applied at the 
grid of tube T, will therefore appear unchanged except fcr d-c level at the 
plate of T, or any intermediate point on the piate load resistor R3. The 
by-pass condenser C is included to insure rapid response. 
+ 300 V 
a 
input 
ii C Shifted 
Signal avy 
Signal 
. Battery 
or divider 
Fige the Voltage-level shifter. 
—This circuit is not original, but the proper person to credit is not know. 
The same circuit is used in the regulated high-voltage supply already described 
[see Sec, 2(b)]. 
