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Next is a differential amplifier using a pair of [[12AU6]] pentodes. | Next is a differential amplifier using a pair of [[12AU6]] pentodes. | ||
The 112 has | The 112 has a differential output intended for directly driving the vertical deflection plates of a CRT. | ||
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 | |||
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. | |||
In one position, the common-mode output voltage is 0 V. | |||
In the other position, the common-mode output voltage is +150 V. | |||
The Type 112 manual recommends 0 V for driving the CRT of the [[511]], | |||
The | and +150 V for driving the CRT of the [[512]], [[513]], and [[514]]. | ||
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)] | * [http://w140.com/tek_112.pdf Tektronix 112 Manual (PDF)] |