112: Difference between revisions

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Next is a differential amplifier using a pair of [[12AU6]] pentodes.

The 112 has ~~an unusual~~ output ~~coupling stage~~.

The 112 has a differential output intended for directly driving the vertical deflection plates of a CRT.

~~It provides~~ output short ~~circuit protection and shifts~~ the common-mode ~~DC level of~~ the ~~differential~~ output to 0 V.

The output terminals of the 112 are on the right side in the rear, so the 112 can sit to the left of an oscilloscope

~~The plate voltage of~~ the ~~final gain stage (just before~~ the output ~~coupling stage)~~ is ~~about~~ +150 V.

and short wires can connect the 112 to the oscilloscope's CRT.

A two-position switch on the rear panel of the Type 112 controls the common-mode output voltage.

~~When enabled~~, the output ~~coupling stage~~ is a a pair of ~~constant~~ current sinks.

In one position, the common-mode output voltage is 0 V.

~~It uses~~ [[6CB6]] pentodes ~~for this.~~

In the other position, the common-mode output voltage is +150 V.

~~This shunt~~ current ~~causes a constant voltage drop across output resistors~~, ~~resulting in 0~~ V ~~at the output~~.

The Type 112 manual recommends 0 V for driving the CRT of the [[511]],

The ~~cathodes of the~~ output ~~coupling stage are supplied by the -150 V rail, allowing them~~

and +150 V for driving the CRT of the [[512]], [[513]], and [[514]].

~~to operate as proper current sources when their plates are at 0V~~.

The shifting of the common-mode output voltage 150 V downward is accomplished

by enabling a pair of 680 μA DC current sinks that cause a voltage drop on 220 kΩ series output resistors.

[[6CB6]] pentodes form the current sinks, with their cathodes tied to -150 V.

The 220 kΩ output resistors also provide short circuit protection.

* [http://w140.com/tek_112.pdf Tektronix 112 Manual (PDF)]

@@ Line 11: / Line 11: @@
 Next is a differential amplifier using a pair of [[12AU6]] pentodes.
-The 112 has an unusual output coupling stage.
+The 112 has a differential output intended for directly driving the vertical deflection plates of a CRT.
-It provides output short circuit protection and shifts the common-mode DC level of the differential output to 0 V.
+The output terminals of the 112 are on the right side in the rear, so the 112 can sit to the left of an oscilloscope
-The plate voltage of the final gain stage (just before the output coupling stage) is about +150 V.
+and short wires can connect the 112 to the oscilloscope's CRT.
+A two-position switch on the rear panel of the Type 112 controls the common-mode output voltage.
-When enabled, the output coupling stage is a a pair of constant current sinks.
+In one position, the common-mode output voltage is 0 V.
-It uses [[6CB6]] pentodes for this.
+In the other position, the common-mode output voltage is +150 V.
-This shunt current causes a constant voltage drop across output resistors, resulting in 0 V at the output.
+The Type 112 manual recommends 0 V for driving the CRT of the [[511]],
-The cathodes of the output coupling stage are supplied by the -150 V rail, allowing them
+and +150 V for driving the CRT of the [[512]], [[513]], and [[514]].
-to operate as proper current sources when their plates are at 0V.
+The shifting of the common-mode output voltage 150 V downward is accomplished
+by enabling a pair of 680 μA DC current sinks that cause a voltage drop on 220 kΩ series output resistors.
+[[6CB6]] pentodes form the current sinks, with their cathodes tied to -150 V.
+The 220 kΩ output resistors also provide short circuit protection.
 * [http://w140.com/tek_112.pdf Tektronix 112 Manual (PDF)]

112: Difference between revisions

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