Tektronix 585 - Page 36

Circuit Description — Type 585
Fig. 4-5. Basic Tunnel Diode Static Currents. (A.) D47 conditions as at point A of Figure 4-4. (B.) D47 conditions as at point D of
Figure 4-4.
If the plate current of V34 is maintained at 4.0 ma the
tunnel diode current will remain at point D. Either by the
rotation of the TRIGGERING LEVEL control or by a signal,
the tunnel diode current can be reduced to point E where
it will switch rapidly to point F. Again L47 has a voltage
impressed across it such that its L/R time constant will soon
permit the tunnel diode current to return to point A. The
time from point F to point A is about 0.3  second.
From the above description you can see that the tunnel
diode has two possible stable states, point A at about 5 ( ’
resistance, and point D at about 420  resistance. It is
the slow change in current of the shunt system around the
tunnel diode, controlled by L47, that prevents the tunnel
diode Trigger Regenerator system from triggering the Sweep-
Gating Multivibrator circuit at too high a rate. If the rate
of the negative trigger pulses sent to the Sweep-Gating
Multivibrator exceed about 1.3 megacycles, unstable trigger 
ing can result.
Two partial diagrams show the current paths for both
tunnel diode static conditions. Figure 4-5a shows approxi 
mate current values for static condition A of Figure 4-4,
and Figure 4-5b shows approximate current values for
static condition D of Figure 4-4. In both cases L47 is not
included because its d c resistance is insignificant for this
purpose.
degenerative resistor (long-tailed), the collector current will
increase at the time D47 switches, but will return to its
original value as soon as C45 charges. The collector cur 
rent of Q44 will drop to its original value even if D47
remains at its D state indefinitely. As soon as D47 switches
from E to A, the collector current of Q44 will decrease until
C45 again changes its charge, and Q44 will then stay
at its original static current value as long as D47 remains
at point A. The collector current pulses of Q44 are never
longer than about 0.3 ^second.
Fig. 4-6. Output pulse of T44. 5 volts per cm. .1 fisec per cm.
Trigger Amplifier Q44
The base of the transistor Trigger Amplifier Q44 is d c
coupled from the cathode of D47 while the emitter is ac
coupled from the anode of D47. Since the emitter of Q44
is returned to its positive supply voltage through a large
TIME-BASE B TRIGGER CIRCUIT
General
Triggering signals from the line, TRIGGER INPUT con 
nector, and Trigger Pickoff circuit of the vertical amplifier
4-6