666 
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required to produce a given deflection) is directly proportional to the 
applied accelerating voltage. As a result, supply-voltage variitions may 
produce serious changes in sensitivity of the recording system. 
(a) Cathode-ray tubes. -- Most of the oscillographs developed at this 
laboratory have used one of three DuMont cathode-ray tube types: 5LP5, SCP5, 
or 3FP5,. All of these tubes have blue screens and the DuMont intensifier 
electrode for additional acceleration of the beam after deflection, The 
short-persistence blue screen is virtually essential for moving-film record- 
ing at speeds greater than about 100 in./sec, and the intensifier circuit 
permits greater spot intensity for a given deflection sensitivity. The 
first two types are 5-in. tubes, while the 3FP5, with 3-in, scrcen diameter, 
permits a more compact unit and has been found very satisfactory, The nega- 
tive second-anode voltages used range from 1100 to 2200 volts, and positive 
intensifier voltages from 1100 to 3000 volts are used. 
(b) Power supplies. -- (i) Modified type 208. The stock DuMont type 
208 oscillograph does not provide adequate writing speed for most recording 
of transients. It can, however, be used at sweep speeds up to about 2 in./msec 
by increasing the intensifier voltage, This is done by addition of a half- 
wave rectifier tube and heater transformer, the high voltage being supplied 
from the original power “neneb enhanc! 
It should be noted that the accelerating voltages of the type 208 os- 
cillograph are very susceptible to line-voltage variations, since a condenser 
input filter without a filter choke is used. This type of filter responds 
very rapidly to increases in rectified input voltage and has a rather short 
time constant for decreases in input voltage, As a result, these oscillo- 
praphs must be used on a well-regulated power line if the sensitivity is to 
be kept constant. With a good power source the over-all sensitivity of the 
oscillograph is reproducible to less than 1 percent over a period of an hour 
or moree 
(ii) Regulated high-voltage supply. A 1300-volt regulated power-supply 
circuit which has been used for multichannel oscillographs and other high- 
voltage requirements is shown in Fig, 13. It is capable of delivering up-— 
wards of 15 ma at 1300 volts with good load and input-voltage regulation and 
negligible ripple. 
> 
—This circuit was originally developed at the David Taylor Model Basing 
