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422: Difference between revisions
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end. The 422 uses tunnel diodes from triggering. The post-deflection acceleration voltage | end. The 422 uses tunnel diodes from triggering. The post-deflection acceleration voltage | ||
is 4900 Volts. | is 4900 Volts. | ||
The trigger circuit in the 422 has a trigger amplifier driving a [[1N3719]] tunnel diode, D375, which | |||
acts as a Schmitt trigger. The trigger amplifier has a nonlinear deadband diode circuit in the | |||
negative feedback path. What results is high gain for small signals (little or no negative | |||
feedback) and low gain for large signals (strong negative feedback). Thus, the signal at the base | |||
of Q364 has a limited swing over a wide range of input amplitudes. The collector current of Q364 | |||
varies between 0 and 9mA. Depending on the position of the trigger slope control, higher collector | |||
current in Q364 either switches D375 from the low-voltage state to the high-voltage state or from the | |||
high-voltage state to the low-voltage state. When D375 transitions from the low-voltage state to the | |||
high-voltage state, it produces a current pulse in the primary of transformer T401, which produces | |||
a current pulse in the secondary of T401. The secondary of T401 feeds another tunnel diode, | |||
D405, and the current pulse switches D405 to the high-voltage state, which starts a sweep. | |||
[http://w140.com/tek_422.pdf Tektronix 422 Manual (PDF)] | [http://w140.com/tek_422.pdf Tektronix 422 Manual (PDF)] | ||