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Circuit Description-Type S8SA
voltage is applied to the base of Q77 4 via R780 from the
+
180-volt unregulated supply.
Diode D793 is a protective device for the power trans-
sistors in the event Q77 4 is removed from its socket. Diode
D793 clamps the base of
Q793
to the +20-volt unregulated
supply. Otherwise the base of
Q793
would rise toward
the + 1 OO-volt unregulated bus.
VERTICAL DEFLECTION SYSTEM
The vertical deflection system for the Type 585A con-
tains an input amplifier, delay line driver, a 186-0 balanced
delay line, a trigger pickoff circuit and an output ampli-
fier driving six pairs of distributed vertical deflection plates
in the CRT. See Fig. 3-2.
The delay line driver and output amplifier are balanced
push-pull stages that provide uniform amplification of the
phase inverted signals from the Plug-In amplifier unit.
The input DC level to the vertical circuit is standardized
at approximately 50 volts. The bandwidth of the verti-
cal amplifier is from DC to 85 MHz or better when used
with a wide band preamplifier such as the Type 82 or 86
units. Any of the 80 series plug-in units can be used to
drive the vertical amplifier or by use of the Type 81 Adapter,
any Tektronix letter or 1 series plug-in units may be used.
Vertical Amplifier Delay Line Driver
The delay line driver for the vertical amplifier consists
of a seven-section push-pull stage connected as a bal-
anced distributed amplifier. Push-pull signals from the pre-
amplifier unit are applied to the distributed amplifier through
toroidal transformer T1014, which helps stabilize the ampli-
fier and prevent common mode oscillations.
Both the grid and plate lines are m-derived low pass
filter sections with the delay time per section being the
same in each line.
Input
from
Plug-In
INPUT AMPL.
7 stage distrib-
uted amplifier
DELAY
LINE
TRIGGER
PICK-OFF
Each section of the distributed amplifier is driven pro-
gressively, as the input signal travels down the line. When
the first section receives a signal from the grid lines, energy
from the plate circuits starts a wave front down the plate
lines toward the delay line. With the delay times of the
plate and grid lines equal, this wave front will reach the
plate terminal of the second section simultaneously with
the arrival of the signal at the grid terminal of this sec-
tion. Energy from the plate circuit of the second section
is fed into the plate line to add to the wave energy from
the first section. Thus the amplitude of the wave front is
doubled at this point. This action is continued as grid and
plate line wave fronts move down their respective lines,
with each plate circuit adding its energy to the wave front
on the plate line at the proper time. The wave at the out-
put of the distributed amplifier (plates of V107 4), is the
result of the addition of the amplification of each of the
individual sections of the amplifier stage. This wave then
travels down the delay line to the output amplifier and
vertical, plates of the CRT.
The plate line is a 186-0 balanced line that is terminated
at each end. The reverse termination network Rl 008-Rl 011,
Rl 009-Rl 012 and Rl 007-Cl 006 is adjustable so the termina-
tion at the output end of the line requires no adjustment.
Current and voltage is supplied to the plate and grid
lines at the output end.
DC shift compensation is provided at the input end of
the plate line. Rl004, Cl004 and Rl005 comprise the com-
pensating time constant to effectively eliminate most of
the DC shift in the amplifier.
Gain of the circuit and the overall gain of the vertical
amplifier is controlled by Rl015 which controls the cathode
bias.
Amplifier stabilization involves many details which are
not required for lower bandwidth systems. Toroid trans-
formers Tl046 and T1014 in the plate and grid lines pro-
vide phase correction and prevent common mode oscilla-
OUTPUT AMPL.
5 stage distrib-
uted amplifier
and output
To Time Base
Trigger Circuit
CRT
Fig. 3-2. Functional block diagram of the vertical deflection system.
3-4
©
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