This Hoyt tube tester is designed to test just a few different types of vacuum tubes which include the UV201 series, WD-11s, WD-12s, and the newer, at that time, UX112, UX120, and UX210 series.
This early instrument requires up to three different batteries when testing vacuum tube performance. The A (filament) voltage is supplied by a 6-volt battery, the B (plate) uses a 22.5 – 45-volt battery and the C (grid bias) value is not specified. The upper scale of the meter measures milamperes (original spelling). The rheostat on the right is used to adjust the filament voltage to the proper value. A 90 volt battery may also be used for testing plate current. In addition the unit may be used as a voltmeter independent of its tube testing functions.
Complete operating instructions are on the back of the cabinet.
Note: The museum also has a Hoyt A. C. Volts 0-150 Meter, the 348 Type 531 on display in the Meter Window in the Wireless Building.