B&K 1076, Instruction Manual

Page: 47 / 64

capacity coupled to the grid of the horizontal output stage. A horizontal drive
control is provided and is of the series type. Maximum capacity, representing
maximum drive to the horizontal output system. The horizontal output trans­
former and high voltage circuits are conventional and are the auto transformer
type using a 6AX4, V-12, as the damper tube, and a 1X2, V-13, as the high
voltage rectifier. The recovered high voltage from this system is approximately
12.5 kv at a 75 microampere load. A width coil is employed to control the
horizontal scan that is shunted across a portion of the horizontal output trans­
former winding. A tap from this same transformer is capacity coupled to the
front panel and is used as the high level A.G.C. keying pulse. V-11, a 6BQ6,
is used for both vertical and horizontal plate drive. Examination of the plate
drive selector switch will show that one section of the switch is used to choose
between a vertical saw driving signal and a horizontal saw driving signal, both
of them obtained from their respective oscillators. The second section of the
switch is used to establish the proper bias for the 6DQ6 for both the vertical
and horizontal position. The neutral position is off which opens the cathode
of this tube, disconnecting it completely.
The next section under consideration is the horizontal output transformer
and yoke shorted turns tester. This is a relatively simple circuit based on a
pulse oscillator that is sensitive to inductance and "Q". The bias that is de­
veloped from this oscillator is fed to V-14A, a DC amplifier, which operates
the test indicator neon lamp. Since shorted turns in yokes and flybacks most
readily manifest themselves as a reduction in "Q" and since the oscillator
circuit is sensitive to change in "Q" a bias voltage change is encountered which
causes the DC amplifier V-14 to draw current and tum on the test indicator
lamp. The change in "Q" reflected by a horizontal output transformer with
as little as one single shorted turns is sufficient to disrupt the oscillator V-14B
and cause the test indicator to light.
The power supply is very conventional. V-15, a 6CA4, is a low voltage
rectifier. You will note that the cathode is fused with a ¼" fuse which pro­
tects the complete power supply from overload due to a short anywhere in
the chassis. The filter consists of C-12A and C-12B and R-34 a 220 ohm
resistor .. This supplies the 200 volts DC required for operation of the chassis.
A +175 volt point is acquired for operation of the video system by dropping
and de-coupling through R-17 and C-12C. A tap on the power transformer
provides a 117 volts AC signal to the selenium rectifier SR-1. The negative 150
volts thus developed is applied to the cathode of the photomultiplier tube. A
tap on the voltage divider from this point to ground which is the sync level
calibrate control, R-15, adjusts the total voltage appearing across V-3A the sync
output stage. A second potentiometer in the voltage divider, R-16,, a 10K
potentiometer, provides the calibrated negative bias appearing on the front
panel of the instrument. The power supply also incorporates an Off-Stand­
by-On switch. When in "Stand-by" position, heater power only is supplied to
all tubes. When switched to the "On" postion, B+ is applied so that the in­
strument is ready for operation merely at the flip of a switch. It might be
well to mention at this point that B+ boost which is derived from the hori­
rr.nntal deflection system is used to power the photomultiplier tube plate, and
B+ boost is also used to drive the vertical saw generator stage. B+ boost is
also used as a source of first anode voltage on the 5BKPV1 scanning tube.
This higher voltage results in improved focus and spot size of the scanning
tube which in tum will result in improved resolution. The vertical blanking
signal for the 5BKPV1 scanning tube is derived from the vertical saw maker
and is applied to the control grid of the scanning tube. The horizontal blanking
information is derived from the cathode of V-3A the sync output stage that
is capacitor coupled to the cathode of the scanning tube. This completes the
circuit description of the Television Analyst.
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