tektronix: 502; Oscilloscope Trigger Amplifier Tube protection

Here is a simple modification to protect the Type 502 trigger amplifier tube (V24) from high amplitude signals when used with external trigger input.

Locate R10, a 1-meg, 1/2 watt, 10% resistor. This resistor runs from ground to a point on the TRIGGER SELECTOR switch. From this point a wire strap connects to the PLUS-MINUS switch. Replace this strap with a 470-k, 1/2 w, 10% resistor shunted by a .001-uf, 500-v discap.

Type 502's with serial numbers above 623 do not require this change.

Source: ServiceScope Aug 1960

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