Tektronix TYPE L, Instruction Manual, Page: 14 / 46

The screen grid of the F irs t Cathode Follow er
is at +100 volts with only the main am plifier
of the unit in operation. When the X10 Am pli­
f ie r is switched into the circuit, the voltage
on the screen is increased and decoupled
through the decoupling network, R5802 and
C5802. This serves to protect the X10 Am plifier
from any slight variations which may be present
in the power supply.
X10 Am plifier
The X10 ac-coupled am plifier consists of
two stages of amplification, V5942 and V6042,
and a cathode-follower output stage, V6132.
The X10 GAIN ADJUST which controls the
amount of degeneration in the cathode circuit
o f V6042 is a front-panel screw driver adjust­
ment. This control regulates the gain of the
X10 Am plifier to adjust for changes which take
place
in the components. For calibrated
operation it is set fo r a gain of ten.
High-frequency compensation fo r the X10
am plifier is provided by the series-shunt peaking
coils L5942 and L6012, and by the series
peaking coils L5902 and L6112. The variable
inductors, L5902, L5942 and L6012, provide
a means fo r adjusting the circuits for optimum
high-frequency response.
Low-frequency peaking fo r the X10
am plifier is provided mainly by C6002A and
C6002B in the plate circuits of V5942and V6042.
With their associated re s is to rs , these capacitors
form a low-frequency " boost" network to com ­
pensate fo r the low-frequency attenuation intro­
duced in the cathode circu its, the screen circu its,
and the RC coupling network between the Second
A m p lifier and the Second Cathode Follower.
The amount of capacitance in the circuit is
fixed , however the amount of attenuation can
be varied with the LOW FREQ. ADJ. control,
R6182, in the grid circuit o f V6132. By adjust­
ing the attenuation to match the capacitance,
low-frequency distortion in the am plifier is
eliminated.
A diode is included in the cathode circuit
o f the F irs t A m p lifier, V5942, to protect the
electrolytic bypass capacitor, C5972. This
capacitor could be damaged if the cathode
circuit voltage went highly negative, as when
the tube is removed without turning o ff the
power.
F or proper operation of the X10 am plifier,
it is important that the Second Am plifier, V6042,
be operated on a certain portion of its character­
istic curve. To allow fo r slight changes in
component values and fo r tube differences,
a V6042 Cathode Current Adj. control, R5922,
is provided in the plate circuit of V5942. The
function of this adjustment is to set the current
through V6042 by adjusting the voltage on its
grid.
C orrect cathode current is indicated
by a voltage drop of 55 volts across resistor
R6072.
The output voltage of the X10 am plifier must
be the same as the output voltage of the F irst
Cathode Follow er in order to present the same
voltage to the grid of V6242 in the Phase
Inverter. This is necessary in order to main­
tain balance in the main am plifier of the plug-in
when switching the X10 am plifier into or out
o f the circuit. The X10 VARIABLE ATTEN.
B A L . control, R6242, in the grid circuit of V6132
is a front-panel screw driver adjustment which
is used to set the bias on the grid of V6132
so that the cathode voltage w ill have the proper
value.
Phase Inverter
The Phase Inverter Stage composed of V6242
and V6342 is a cathode-coupled phase inverter
which converts a single-ended input signal into
a push-pull output signal and provides a gain
o f two.
The GAIN ADJUST control (R6392) in the
cathode circuit of the Phase Inverter sets
the gain of the main am plifier of the plug-in
unit to correspond with the front-panel ca li­
bration. This control is a front-panel screw ­
d riv e r adjustment.
The VARIABLE (VOLTS/CM) control, R6352,
located between the two cathodes, regulates
the gain of the stage over a 2.5-to-one range
by varying the amount of degeneration in the
cathode circuit. Maximum gain occurs with
the control in the CALIBRATED position.
If the no-signal dc voltage levels on the
Phase Inverter cathodes are not equal, current
w ill flow through the V ARI ABLE resistor causing
a change in the gain of signals passing through
the stage. Voltage on the cathode of V6342
may be adjusted to balance that of V6242,
eliminating current through R6352. This is
3-2
Circuit Description - Type L Plug-In
AA