Maker's Name: 
Amalgamated Wireless (Australasia) Ltd
Where made: 
17 × 17 × 10 cm

This is a Vacuum-Tube Volt Meter (VTVM), operating from an internal AC supply. It has a double triode in a cathode-follower configured Wheatstone bridge circuit. Input voltage applied to one triode grid unbalances the bridge, and the meter indicates the voltage applied by the the extent of the meter needle deflection.

Input to the grid has a resistance of 10 megOhms. Taps on the input resistor give different voltage scales.

AC input voltages are rectified by a diode valve, and the half-wave rectified DC applied to the triode grid.

The meter can also indicate resistance values by applying an internal 3 Volts DC through a series resistor. The voltage applied to the triode grid depends on the value of the external resistor being measured. Different values of resistance give different resistance scales on the meter.