Tektronix 1A1, Инструкция по эксплуатации

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Circuit Description— Type 1A1
Follower stage (Q123/Q143) provides a low-impedance
drive to the Input Amplifier stage (Q124/Q144). The signal at
the source element of Q122 is DC coupled to the base of
Q124.
A plastic cover is placed over Q123 and Q143 to min­
imize the differential variations of ambient temperature be­
tween the transistors.
Input Amplifier (Q 1 2 4 /Q 1 4 4 )
This stage is an emitter-coupled paraphase amplifier.
It converts the single-ended input signal applied to the base
of Q124 to differential current signals at the collectors.
Both emitters are long tailed (through R127, R147, R148 and
R149) to the —150-volt supply for greater stability with re­
spect to transistor parameters.
As mentioned previously, the second section of the VOLTS/
CM switch controls the deflection factor for the first four
steps by changing the emitter resistance of this stage, thus
controlling the gain of the stage. At the .005 VOLTS/CM
POSITION, gain ratio is 10 to 1; at the .05 position, gain
ratio is 1 to 1. For the .005 position, the .005 V/CM GAIN
adjustment (R128A) is adjusted so the 10-to-l gain ratio is
accurate. Precision resistors set the gain ratio accurately for
the three remaining steps.
To balance the emitters of Q124 and Q144 under no-sig­
nal conditions, the VOLTS/CM switch is set to the .005
position and the .005 V/CM VAR ATTEN BAL control (R130)
is adjusted for no trace shift while the VARIABLE VOLTS/CM
control is rotated back and forth. After noting the posi­
tion of the trace, the VOLTS/CM switch is set to .05 and
.05 V/CM DC BAL control (R148) is adjusted to position
the trace to the previously noted position. When the stage
is correctly balanced, the emitters will be at the same volt­
age and there will be no current between emitter resistors
regardless of the VOLTS/CM switch positions.
The value of the collector resistors R126 and R146 is
chosen to provide proper base-emitter junction temperature
compensation for their respective transistors. Cl 25, Cl 52
and Cl 56 provide a means for adjusting the high-frequency
response to compensate for losses introduced by tempera­
ture compensation resistor networks and to balance the
output of the two channels.
Resistors R124, R125, R144 and R145 develop the signal
for application to the following stage.
The second Emitter Follower stage (Q153A/Q153B) cou­
ples the push-pull signal from the Input Amplifier to the
Output Amplifier first stage. In addition, the second Emit­
ter Follower stage provides the necessary low-impedance
drive for the circuit card connectors, the PULL FOR INVERT
switch (SW405), and the interconnecting leads.
When the PULL FOR INVERT switch is set to the normal (in)
position, the signal at the emitter of Q153A is coupled
via the switch contacts to the base of Q414 (Output Am­
plifier) and the signal at the emitter of Q153B is coupled
via the switch contacts to the base of Q404 (Output Am­
plifier). Thus, the display will have the same polarity as
the input signal applied to the Channel 1 connector. If
the input signal is positive-going at the Channel 1 con­
nector, for example, the display waveform will also be
positive going. However, when the switch is set to the
invert position, the display will be inverted because the
switch reverses the signal leads to the bases of the fol­
lowing stage. Thus, a positive-going signal will be dis­
played as a negative-going waveform.
The INV BAL control (R152) in the base circuit of Q153A
DC balances the outputs of the second Emitter Follower
stage so there is no trace shift when the PULL FOR INVERT
switch is changed from normal to invert under no-signal
conditions.
Output Amplifier First Stage (Q 40 4/Q 4T 4 )
This stage is an emitter-coupled push-pull amplifier pro­
viding a total gain of about 2. Collector current for the
stage is supplied through the diode switches (see Fig. 4-2).
There are two gain controls located in the common-
emitter circuit of Q404 and Q414— VARIABLE VOLTS/CM
control (R408) and GAIN control (R409). Both controls vary
the emitter degeneration and, thus, affect the gain of the
stage. With the VOLTS/CM switch in the .05 position and
the VARIABLE VOLTS/CM control set to CALIB, the GAIN
control is adjusted so the CRT deflection agrees with the
setting of the VOLTS/CM switch. The VARIABLE VOLTS/CM
control has a gain attenuation ratio of 2.5 to 1. However,
this ratio is actually greater than 2.5 to 1 due to SW409.
As the VARIABLE VOLTS/CM control is rotated a few
degrees from the CALIB position, SW409 closes and shorts
out R409. Gain increases, thus providing overlapping cov­
erage between the calibrated VOLTS/CM switch positions.
The POSITION control (R422), connected between the
differential inputs to the diode switches, provides differ­
ential currents that act as positioning signals superimposed
on the output signal currents of Q404 and Q414. When
the POSITION control is set to its electrical center, no cur­
rent flows in either leg. When the POSITION control is
moved to either end from center, a change of about 0.6
volt per side occurs at pins 1 and 3 of the interconnecting
plug to the oscilloscope. This voltage range corresponds
to about 12 cm positioning range at the CRT.
Diode Switches
The push-pull signal from the Output Amplifier first stage
is applied to diode switches D421, D422, D423 and D424.
These diodes act like a double-pole double-throw switch.
Each pair, D421 and D422 or D423 and D424, is on while
the other pair is off. Switching of the diodes to connect
or disconnect a channel is controlled by the MODE switch
via the Switching Multivibrator in the Channel Switching
Circuit.
Assume Channel 1 is turned on (MODE switch is set to
CH 1) and the POSITION control is centered. The state of
the Switching Multivibrator (Q305 and Q315) is such that
+7.7 volts from its conducting transistor Q305 is applied
to cathode junctions of Channel 1 shunt diodes D422 and
D423 (see Fig. 4-2). The lowest voltage seen by the cathodes
of the diodes switches is +4.6 volts at the cathodes of
Channel 1 series diodes D421 and D424. The series diodes
conduct and the drop across these diodes sets their anodes
at +5.6 volts. The +5.6 volts reverse biases the shunt
diodes. With the series diodes conducting, the Channel
® i
4-3