Circuit Description - Tektronix Type B Plug-In Instruction Manual

+ 300V
General
The Type B Plug-In Unit has a maximum sensitivity o f .05
volts per centimeter dc and .005 volts per centimeter ac.
The circuit consists o f one stage of amplification preceded
and followed by cathode followers, with an additional, ac-
coupled stage inserted in the three most sensitive positions
of the VOLTS/CM switch.
Input Connectors
There are two input connectors which can be switched
into the input circuits by SW3022, the INPUT SELECTOR
switch. This switch is wired physically so at to reduce coupl­
ing between inputs to a minimum. Blocking capacitor C3042
(C3012 S /N 101-3300) is shorted out in the DC positions ot
the selector switch.
Input Attenuators
The VOLTS/CM switch inserts frequency-compensated at­
tenuators into the input circuit. Four attenuators are used
singly or in tandem pairs to produce nine fixed sensitivities.
The ac-coupled preamplifier, V4302, (V3302 S /N 101-3300),
is switched into the circuit in addition to the attenuators in
the three most sensitive positions to give a total of twelve
fixed sensitivities.
101-3300) is inserted in the AC ONLY positions o f the
VOLTS/DC switch. The XI attenuation network compensates
for lead inductance in the input circuits.
Preamplifier
The preamplifier stage consists of V4302 (V3302 S /N 101-
3300) as a single ended pentode voltage amplifier, V4102B
(V3502A S /N 101-3300) as a cathode follower driver for the
amplifiers and V4102A (V3502B S /N 101-3300) as a low-
impedance voltage setter for the preamplifier screen grid.
R4352 (R3332 S /N 101-3300), a front-panel screwdriver con­
trol labeled G A IN ADJ. 2, adjusts the degeneration in the
cathode of V4302 (V3302 S /N 101-3300) to set the gain of
the stage. The chassis-mounted screwdriver control, labeled
LOW FREQ. COMP, adjusts the time constant of the grid
circuit coupling network. This network, in combination with
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Blocking capacitor C3042 (C3022 S/N
SECTION 3
DESCRIPTION
the low-frequency boosting network, R4022, C4022A (S/N
3301-up) provides low-frequency
less than 50 cps.
DC Balance
The DC BAL control, R4402 (R3642 S /N 101-3300), pro­
vides an adjustable, dc grid voltage for V3552 (V4102 S/N
101-3300) so that its cathode is at the same dc potential
as the cathode of V3402 (V4002 S /N 101-3300). When this
control is properly set, no change in vertical positioning
w ill result when the VARIABLE control is rotated.
Input Cathode Follower
The input cathode follower, V3252 (V3502A S /N 101-
3300), isolates the input circuits from changes in capaci­
tance as the VARIABLE control is rotated. R3282 (R4012 S/N
101-3300) is a current-limiting resistor to limit the grid current
in the event an excess voltage is applied to the input.
Amplifier
The am plifier stage, V3402 and V3552 (V4002 and V4102
S /N 101-3300), is a common-cathode phase-splitter ampli­
fier. Coils L3402 and L3582 (L4202 and L4402 S /N 101-3300)
form peaking networks in the plate circuits.
3301-up) provides the current for the amplifier plates, and
a tap to the heater string provides a low impedance at this
point.
The VARIABLE VOLTS/CM control, R3512 (R4062 S/N 101-
3300), varies the gain over a 2V2-to-l ratio by varying the
degeneration in the cathode circuit. R3542 (R4102 S /N 101-
3300), labeled G AIN ADJ. 1, varies the current in this stage
to set the gain to agree with the front-panel calibration.
Vertical positioning is produced by two dual potentio­
meters connected to the plates of the am plifier so that cur­
rent through one plate load is increased as current through
the other plate load is decreased. Since the am plifier is dc
coupled beyond this point, the change in plate voltage
which occurs changes the position of the trace on the cath­
ode-ray tube. The current drawn by these potentiometers is
added to the heater string to provide the additional cur­
rent required by V4302 (S/N 3301-up).
C IR C U IT
compensation down to
R3402 (S/N
3 - 1