In order to draw the complete characteristic curves for vacuum tubes requiring a large cutoff voltage, the grid step output from a Tektronix curve tracer must be amplified.  The amount of amplification depends on the tube under test, and if a pentode, depends on the screen voltage.  An EL34 requires a relatively modest negative grid voltage to reach cutoff for a power pentode, but a KT88 or 6L6 will require -45v to -60v to reach cutoff, and much more when triode connected.  Even more extreme are the low mu power triodes like the 2A3 or 300B, which require upwards (downwards?) of -140v to reach cutoff.  

This unit is specifically designed to work with Tektronix type curve tracers.  It will likely work with other curve tracers as well, but the interconnects will be different.  Ultimately, this is a relatively straightforward high voltage amplifier, designed for negative voltage amplification.  As such, it could be used for any application that requires such an amplifier.  

The Grid Step Amplifier is composed of three basic sections: +5v power supply, -210v power supply, and the 10x amplifier.  The unit is designed to run on any power supply input voltage from 9-30vdc.  The max current draw at 9v is 1000mA.  Load current diminishes as the input voltage is raised (20v input = 310mA current draw).  The power supply input has reverse polarity protection and transient voltage suppression.  The unit is shipped with a 15vdc, 800mA power supply.

The input power supply voltage is routed to the positive and negative supplies.  The positive supply utilizes a standard three terminal 5v linear regulator.  The negative supply is more sophisticated to enable the high voltage output.  An isolated flyback dc-dc convertor generates the required -210 volts. 

These asymmetrical voltages power the high voltage precision op amp.  The gain is set to 10x (non-inverting) by 0.1% resistors and the output current is rated at a continuous 20mA minimum.  The op amp is short circuit and over temperature protected.  The use of a 50 ohm output resistor adds additional protection and stability.  The input of the op amp is protected from transient and continuous over voltage situations.  (It is an easy mistake to not invert the Step Generator Voltage before connecting to the input of this device).  

Gain: 10x (non-inverting, DC coupled)

Input Voltage: +0/-20v (input protected against over-voltage conditions: +30v minimum)

Input Impedance: 25K ohms

Output Voltage: +0/-200v

Output Current: 20mA minimum

Output Impedance: 50 ohms

Power Supply: 9-30 vdc @1000mA max - center positive

Dimensions: 4 1/16" x 2 5/8" (extruded aluminum case)