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108
T Y P E
6 0 3
E L E C T R O N I C M U L T I P L I E R
---
TI c u t o t t 3
Potential
@
Anode Potential
Output from Mult~vibratar
@
Anode Potential ot
First Clipper ( 1 , )
Time
+
0
@
Anode Potential at
Second Clipper ( T p l
Time*
Figure 104.
Output Voltages o f Multivibrator and
Triode Clippers
grid currenr will increase rapidly and cut down
the potential at G1 rapidly.
The slight increase
in anode current through
T1
resulting from a posi-
tive pulse will produce a slight drop in anode
potential at point AT. However, a negative pulse
applied at C will drive the grid of
T1
negative. If
the negative pulse is of more than 8 volts,
TI
will
be cut off. Actually, the negative pulse from the
multivibrator may approach -100 volts and be an
almost instantaneous shift; hence,
T1
is almost in-
stan~aneously cut off, and point AI rises almost
instantaneously to
+
1
?
0 volts (ignoring the bleed-
er circuit from the -100 volt line through R4,
R::,
RL1 to the
+
1
? O
volt line). Point A T remains at
approximately + I
? O
volts as long as point GI is
at
-8
volts or less, consequently whatever the shape
of the applied waveform is below the -8 volt line,
the output of
T1
will be a square-topped wave.
This is indicated at B of Figure 104. However,
to obrain a truly square wave the output of
T1
must pass through
T.
so that the lower portion
can be clipped.
As previously mentioned,
Tz
cannot conduct as
long as
T1
conducts. However, when
T1
cuts off,
point A1 rises t o approximately + I 50 volts and
point Gz becomes positive, thus making
Tz
con-
ductive.
When
T2
conducts, point A2 is at ap-
proximately
+ Y O
volts.
Since
T 2
cuts off at -8
volts and the pulse from
T1
is approximarely 100
volts, the variation from a square wave in the
waveform from the output of
TI
will not be re-
flected in the output of T2, and a true square wave
is obtained at the output of
Tr
as indicated in Fig-
ure 1O4C. Bear in mind that the waveforms shown
in Figure 104 are theoretical. Practical waveforms
differ somewhat because of inductive effect, inter-
electrode capacity, etc.
As both the mulrivibrator and clippers are volt-
age devices, their output cannot be utilized directly
as a source of pulses for the electronic unit.
T o
actually supply the pulses for the unit, power rubes
controlled by the clippers are used.
The actual circuit for the generation of pulses
in this unit is shown in Figure 101. This circuit
is taken from the A chassis circuit (Section 23B).
Observe that the cathodes of rhe multivibrator are
tied to the -100 volt line and that the anodes are
tied to rhe anode of a VR-110 tube.
Thus, the
anode voltage supply is taken across the VR-150'
voltage regulating tube.
The voltage r e p l a t i n g
tube is a gas-filled, cold cathode tube which has the
property of maintaining a constant voltage drop
within its operating limits.
The amount of the
voltage drop is determined by the gas used and the
physical structure of the tube elemenrs. The VR-
150 "fires" at 18
?
volts and then maintains a con-
stant drop of 110 volts within the range of
?
through 40 milliamperes anode currenr.
This
method provides a constant anode voltage for the
multivibrator even with variations in the supply
and thus maintains a constant oscillating fre-
quency. The 3 000 ohm resistor between the +I 10
volt line and the VR-I?O anode limits current
through the VR-I
? O
to 3 0-3
?
ma and provides
the means for compensaring for supply voltage
fluctuations.
Variations in supply voltage result
in variations in current through the VR- I 5
O
and
in proportional variations in IR drop across the
3000 ohm resistor, rhus maintaining a constant
IR drop across the VR- I 5 0.
The voltage pulses at the anode of tube 2 of the
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