Component withstand voltage measuring instrument circuit

In the electronic manufacturing process, it is often necessary to measure
the back voltage of transistors, diodes, voltage regulators, thyristors, etc. and the withstand
voltage of capacitors. To this end, this section introduces a simple withstand voltage measuring
instrument. Its output voltage is continuously adjustable, up to 1500v.
    Here's how it works.
    The measuring instrument circuit is shown in Figure 5-27.
The 6V voltage output by transformer T is rectified by VD5 and filtered by C3, and then is provided
to the base voltage of the adjustment tube VT. Adjusting RP can control
the conduction degree of VT, that is, controlling the voltage of collector point M
to change between 4-1400y. The high voltage winding outputs 500v voltage. By C． , VD1 ~ VD4 composed of voltage doubler rectifier circuit rectification, G filter output
1400V high voltage. During measurement, the device under test is connected between M and N, the resistance of RP is adjusted small, the base potential of VT decreases, and the potential of point M increases.
Until the milliamp meter indicates the rated reverse current of the tube under test (the low-power tube under test is less than 0.1 ImA, and the high-power tube is preferably less than ImA). At this time,
the voltage value indicated by the voltmeter is the back pressure under the reverse current. When using a large value resistor, connect the resistor between M and N. Divide the voltmeter reading
by the milliammeter reading, or R=V/I. Each time it is used up, the special RP reaches the maximum, causing the output voltage to return to the lowest point voltage of 4V.