Tektronix TYPE 109, Инструкция по эксплуатации

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Circuit Description— Type 109
Resistors R678 and R679 set the current passed by V679
at a value which allows this tube to regulate properly
within the line-voltage operating ranges specified for the
Type 109. The regulator tube compensates primarily for
line voltage changes within those operating ranges. The
voltage across the terminals of V679 and the output of
the supply is maintained by V679 at nominally 105 volts.
Capacitor C679 reduces the amplitude of the spikes
that originate from the mercury switch. Resistor R660 serves
as an overload fuse for this supply. The purpose of R660
is similar to that of R610 in the 10-volt supply.
The polarity of the output of the 105-volt power supply
is controlled by the PULSE POLARITY switch, SW679. By
grounding either of the output leads, either polarity of
output voltage can be obtained. The output of the power
supply is applied to the pulse amplitude control network.
Pulse Amplitude Control Network
The 100V SET control, R690, sets the voltage across the
AMPLITUDE control, R696. The current drawn from the ± 105-
Volt Power Supply by the pulse amplitude control network is
approximately 5 ma in all positions of the VO LTAG E
RAN GE switch, except EXT. PWR. This means that the
voltage drop across R690 also remains constant regardless
of the position of the V O LTAG E RAN GE switch. The 100V
SET control is adjusted so that the voltage at the ungrounded
end of the AMPLITUDE control is set to exactly 100 volts.
The voltage across the AMPLITUDE control is always equal
to twice the setting of the V O LTAG E RAN GE switch. The
pulse amplitude control network is designed to provide a
nearly constant load on the power supply while at the same
time dropping the voltage across the AMPLITUDE control
to the proper value. The AMPLITUDE control, when used
in conjunction with the V O LTAG E RAN GE switch, permits
the application of any voltage between zero and 100 volts
through resistors R751 and R753 or R756 and R758 to the
charge lines (see simplified schematic diagram in Fig. 4-3).
Approximately 250 microseconds is allowed for a single,
interconnecting charge line capacitance to be charged to
the voltage obtained from the wiper arm of the AMPLITUDE
control. The 250-microsecond time duration is the open-con-
tact time of the mercury switch. Using separate charge lines,
about 1.8 milliseconds charging time is available at a
nominal repetition rate of 320 cps from each contact. This
is the total time that it takes for the reed to leave the
contact, go to the other contact and return.
Mercury Switch
The two charged coaxial cables are alternately discharged
through the 50-ohm output load by the mercury switch
SW750. As the mercury switch closes, one of the charge
lines momentarily acts as voltage source (see Fig. 4-3). The
internal impedance of this voltage source is 50 ohms and
the load impedance is also 50 ohms. Consequently, only one
half of the voltage to which the line was charged appears
across the load. (This explains why the ranges of the VO LT­
A G E RAN GE switch are only half the actual charging
voltage.)
If we assume that the line was originally charged to +100
volts, then a +50-volt output pulse is obtained. A 50-volt
pulse also travels down the charge line toward the open
end (called the back wave). As the pulse reaches the open
end, it is reflected in phase and returns toward the mercury
switch. As the reflected pulse reaches the mercury switch,
the charge in the cable drops to essentially zero and the
output pulse ends. The duration of the output pulse is thus
twice the transit time of the charge line. The output pulse
contains all the energy (excluding losses) originally con­
tained in the charge line.
As the mercury switch opens, it allows the charge line
to recharge preparatory to the generation of the next pulse
by that line. When the reed of the mercury switch dis­
connects from one contact, it moves across and closes with
the other contact. This then discharges the second charge
line in the same manner as the first. The mercury switch
then continues this operation of discharging first one and
then the other charge line. If both charge lines are charged
to the same voltage, then both sets of output pulses will
have the same amplitude. Furthermore, if both charge lines
are exactly the same length, both sets of output pulses
will have the same duration. The amplitude, polarity, and
duration of the alternate sets of pulses can be made the
same or different by selecting the charge voltages and
charge lines. Fig. 4-3 shows a waveform obtained when
different length charge lines are used.
A single charge line may be used to generate both sets
of output pulses by connecting one end of the cable to
the 50Q CH G . LINE 1 connector and the other end of the
cable to the 50 Q C H G . LINE 2 connector (see Fig. 4-4). The
operation of the Type 109 is the same as before except
that instead of having an open-ended coaxial cable, the
cable is terminated in a resistance of approximately 52 k.
This high resistance produces practically total reflection.
There is a dip in the center of the generated pulse w ave­
form (see Fig. 4-4) due to capacitive coupling of the back-
w ave from the unused contact. Other than this, however,
there is essentially no difference between the pulses gen­
erated by a single line and the pulses generated using two
separate lines. The panel connectors act as 0.25 nanosecond
delay lines causing pulses to be 0.5 nanoseconds longer
than when one end of the cable is open. Use of a single
charge cable insures that the alternate sets of pulses have
exactly the same time duration.
The charge lines used with the Type 109 can be charged
by an external source of power as well as by the internal
power supplies. If an external source is used, the charging
current is applied through the EXT. POWER OR M ONITOR
connectors, the 47k resistors, and the 4.7k resistors to the
charge lines. The advantage of using external charge power
lies in the ability to use higher charge voltages to generate
high amplitude pulses.
The two 47k, 2-watt resistors limit the external voltage
applied to about 600 volts and the output pulse amplitude to
approximately 300 volts. Another advantage of using an
external charging source is that a negative charge can
be applied to one charge line while a positive charge is
applied to the other line. This permits the generation of
alternately positive and negative pulses.
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