Tektronix 3B2 TIME-BASE Instruction Manual page 14

Q224 turns off, causing disconnect diode V252 to conduct and
(about 4.1 ma) to make D215 triggerable.
TIME/DIV switch SW260 selects the resistors and capaci-
The output of the Miller circuit (pin 8 of V261B) couples
The sweep takeoff for the digital unit is also at this point.
The output amplifier is a cathode-coupled paraphase am-
amplifier. Positioning is accomplished by changing the de
level on the grid of V314B with potentiometer R319 (POSI-
TION control).
CLOCK PULSE GENERATOR
This circuit develops the clock-pulse signals used in the
digital readout unit. The circuit also contains the DIGITAL
RESOLUTION switch used to select time measurement
units for the digital display unit.
The clock (Q490) is a crystal-controlled 1-mc oscillator.
The signal from the collector of Q490 couples through C492
to the base of Q494. This transistor is an over-driven ampli-
fier that produces pulses at 1-sec intervals. These pulses
are coupled to the DIGITAL RESOLUTION switch and to the
There are four Counter boards. Each board is a divide-
by-ten device; that is, for every ten pulses in, there is one
pulse out. Thus, with the output of one counter fed to the
next, four successive divisions-by-ten occur. Outputs from
the clock, and from the counters provide pulses at intervals
of 1 psec, 10 usec, 0.1 msec, 1 msec, and 10 msec. Each of
these outputs is connected to the DIGITAL RESOLUTION
switch where it selects which of the five pulse intervals is
With the DIGITAL RESOLUTION switch in the .1 «5S posi-
tion, pin 16 of P22 is connected to the 1-MC clock 'oscillator.
This signal may pass from pin 16 to the digital unit where it
can be used to generate pulses with 0.1-usec intervals.
Note, however, that not ail digital units can use this signal.
The DIGITAL RESOLUTION switch also selects the position
of the decimal point and unit of measure (S, MS, 4S) when
the digital unit is displaying time measurements. When the
Q465 turns on with one input pulse, turns off with the next