This circuit, obtained from a publication of the 60's, is the typical example of a voltmeter tube complete, using an analog instrument. The input impedance of the order of 20 M ohms, guaranteed an excellent measurement accuracy in bench works.
In addition to the tubes, the critical component is the transformer, remembering that in this type of application the resistors must be precision.
We also observe the use of voltage regulating tubes type VR-150 that guarantee the stability of the power supply of the circuit, important in this type of application.
The instrument is a milliammeter with 1 mA full scale. In a modern application a common analog multimeter can be used in this range of currents.
The input switch selects the voltage range according to the values ??indicated. Note that there is a small battery used for circuit polarization.
The complete diagram of the voltmeter is shown in figure 1.
