Circuit Description— Type M
The signal is taken from the junction of R5326 and R5327
located in the common-emitter circuit of Q5324 and Q5334.
The R5326-R5327 junction is a convenient low-impedance
point for extracting the signal without affecting the M-Unit
bandwidth and with least pick up of switching transients
when using the M unit in the CHOPPED mode.
With the VAR. GAIN control set to the CALIB. position,
the signal amplitude at the junction is about 80% of that
at the grid of V5323. At the base of Q5344, the signal am
plitude decreases to about 60% of that at the grid of
V5323. The gain of the Channel A Signal Output Ampli
fier is about 160; Q5344 has a gain of approximately 10
and Q5354 has a gain of about 16. The overall gain of
160 results in an output signal of approximately 2 volts at
the "A " SIGNAL OUT connector for each centimeter of
vertical deflection on the crt. Bandwidth of the amplifier
is dc to about 1.0 me —3 db (750 kc —3 db, S/N 101-
2759), and the rolloff is long and gradual.
The OUTPUT DC LEVEL control R5354 is the current
source for adjusting and matching the dc level at the "A "
SIGNAL OUT connector to the level at the channel A input
connector. Normally, when making the adjustment, the A
input connector is grounded and the OUTPUT DC LEVEL
control is adjusted to obtain a voltmeter reading of zero
at the “ A ” SIGNAL OUT connector. This control com
pensates for variations between Nuvistors and the effects
of tube aging. The high gain of the Channel A Signal
Output Amplifier and the relatively wide variation in trans-
conductance between Nuvistors makes the control some
what sensitive. Therefore, the control should be adjusted
carefully when matching dc levels. Exact zero volts is
difficult to obtain and a setting within a few hundred milli
volts of zero is adequate for triggering purposes. How
ever, if this amplifier is used as a dc preamplifier, the
control has to be adjusted more carefully for a setting less
than a few hundred millivolts from zero.
S /N 2760-up
Above serial number 2759, Q5344 is replaced with a
double transistor. The A side of the transistor performs
the same basic functions as did Q5344. The B half com
prises a comparator circuit with A side.
When channel A was initially set up the DC BAL con
trol was adjusted for no movement of the trace as the VAR
GAIN control was turned away from its CALIB position.
The GAIN ADJ control was then adjusted to provide the
proper gain. When the above adjustments are made, there
will exist a given potential on the base of Q5344A and
the base of Q5344B. The OUTPUT DC LEVEL control is
then adjusted for a zero volt dc level at the "A " SIGNAL
OUT connector.
If the Type M is now moved to another oscilloscope
and the DC BAL control is adjusted properly, the given
potential on the bases of Q5344A and Q5344B will be
close to those which existed the first time the OUTPUT
DC LEVEL was adjusted. Since the OUTPUT DC LEVEL
control is already adjusted for these potentials, the dc level
at the “ A ” SIGNAL OUT connector is still close to ground.
SWITCHING CIRCUIT
Ring Counter
The Ring Counter consists of Q6315, Q6325, Q6335 and
Q6345 and associated circuitry. Each transistor controls
one Input Amplifier channel. The Ring Counter is tetra-
stable; that is, each of its four states is stable and a trigger
from the Switching B.O. Q6350 during multi-trace operation
is required to make it switch channels. When triggered,
the Ring Counter performs the task of sequencing and gat
ing the Input Amplifiers.
When only one channel is on (single-trace operation),
Q6350 is inoperative and the Ring Counter remains switched
on or “ locked" on the one channel, keeping it on. When all
channels are turned off (all MODE switches set to OFF), the
Ring Counter is in a quiescent state.
In the following discussion the Ring Counter is described
under four modes of operation. These are: (1) all channels
off, (2) single-trace operation, (3) alternate multi-trace
operation, and (4) chopped multi-trace operation.
(1 ) All channels off.
With all MODE switches set to
the OFF position, the Ring Counter is placed as close as
possible to a quiescent or static condition. All transistors
in the Ring Counter are reverse-biased except the one that
is switched off last. Assume for this discussion that the
channel A MODE switch was set to the OFF position last.
The base voltage for each transistor is determined by a
matrix of three 10.1-k resistors located in each base circuit.
Matrix currents through R6310, R6320, R6330, R6340 and
R6360 hold all bases at about +6.5 volts. The common
emitter bus is held at about +6.8 volts by the emitter cur
rent of Q6315 (channel A turned off last). The collector
bus rests at about —7 volts by the current drawn by Q6315
and the matrix circuits.
The voltage at the collector of Q6315 is held at about
+3.7 volts by the current through Q6315; the remaining
collectors are held at about —1.4 volts. With three tran
sistors cut off, the —1.4 volts at the collectors of these
transistors reverse bias their D5345/D5347 diodes. Chan
nel A diodes D5345 and D5347 are forward biased by the
+3.7 volts at the collector of Q6315, but no signals are
passed since the MODE switch is set to OFF.
(2 ) Single-trace operation.
When the channel A
MODE switch is turned on, the voltage at the base of
Q6315 decreases from about +6.5 volts to about +5.9
volts since the base is no longer connected to R6310. Cur
rent through Q6315 increases slightly, causing the collector
voltage to change from +3.7 volts to about + 4 volts.
The voltage at the other collectors remains at about —1.4
volts and the common collector bus drops slightly to about
—6.9 volts. The diode gate for channel A, being forward
biased, couples the channel A signal from the Input Am
plifier through the MODE switch to the Output Amplifier.
The diode gates for the other channels remain reverse
biased.
Total collector current for Q6315 is about 9 ma . . . 5 ma
through R6317 and 4 ma through the channel A diode
gate. The total current through R6316 is the sum of the
base and collector current of Q6315.
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