Tektronix 507, Инструкция по эксплуатации

Страница: 15 / 60

CIRCUIT DESCRIPTION
SWEEP
A linear triggered sweep is available with
eleven fixed, accurately timed sweeps ranging
from .02 microseconds per centimeter to 50 mi­
croseconds per centimeter. The basic waveform
is generated by a pentode clamp with a cath­
ode-follower bootstrap linearity corrector. Push-
pull deflection is accomplished at output level by
addition of a plate-output unity-gain phase-
inverter stage, shown on the Horizontal Ampli­
fier circuit diagram.
Trigger Phase Changer
A trigger selector switch selects the source of
trigger signal and V4 and V I4 reverse the phase,
if necessary, to provide the trigger amplifier with
the required negative signal.
Trigger Limiter Amplifier
The trigger limiter stage V24 operates with
zero bias. The negative pulse from the trigger
inverter-amplifier drives this tube to plate-cur-
rent cutoff. Choice of the proper value of quies­
cent plate current and the use of a plate-load
resistance of low value results in a very steep
positive pulse limited in amplitude to about 10
volts. This positive pulse is then used to drive
V34.
Trigger Switch Tube
The resulting negative pulse at the plate of
V34, coupled through the coupling diode V I02
to the plate of the minus multivibrator V I05, trig­
gers the sweep.
Trigger Coupling Diode
The trigger-coupling diode V I02 serves to dis­
connect the plate of the trigger-switch tube V34
from the plate of the negative multivibrator tube
V I05 when the plate voltage of V I05 drops be­
low that of V34.
Multivibrator
V I05 and V I15 operate as a plate-coupled
monostable multivibrator for the purpose of
m
converting a triggering pulse into a pulse of con­
trollable duration suitable for operating the
sweep generator and unblanking circuits. The
SWEEP STABILITY control, by varying the bias
on the grid of V I05, determines the optimum
point of triggering.
Duty Cycle Limiter
The duty-cycle limiting circuit is designed as
a protective circuit to prevent the horizontal
amplifier V324 from exceeding its dissipation
rating. This is accomplished by sampling the out­
put of the plus multi cathode-follower V I33 and
feeding this voltage through an integrating net­
work (R125-C125) to the grid of the difference
amplifier V I16 (pentode section). A rise in the
voltage at this grid forces the grid of the minus
multi V I05 toward cutoff which results in a multi­
vibrator waveform shorter than normal for the
sweep speed being used. Since the length of the
multivibrator waveform determines the sweep
length, as the duty cycle is increased the sweep
length is shortened.
A compensated divider located at the grid of
the triode section of V I 16 provides a second
means of controlling the multivibrator. This cir­
cuit is not duty-cycle conscious, but rather sam­
ples the trigger lock-out circuitry. During the
trigger locked-out configuration the grid of the
triode section is pulled down sufficiently to lock
out the multivibrator until the trigger-lockout cir­
cuit is reset.
Sweep-Trigger Lockout
When the SWEEP MODE switch is in the
SINGLE SWEEP position the thyraton V49 con­
ducts and its plate drops. This action produces
two results: (1) It pulls down the grid of the
triode section of V I16 and switches all of the
current to the pentode section. This cuts off V I05
and forces the multivibrator to remain in its
quiescent state; (2) It pulls down the screen of
V34 through the cathode follower V63A and V34
cuts off. With V34 cut off, the triggers are pre­
vented from reaching plate of V I05 and initiat­
ing a sweep.
CIRCUIT DESCRIPTION — TYPE 5 0 7
2-1