Valve Characteristic Meter MK 1

First model of the AVO Valve Characteristic Meter, very different from the 2-panel valve tester it superceded.  The later Mk. 2 looked similar but with added handles on the front panel, a larger back opening, and longer legs to allow a book to be stored underneath.  Later models had an EA50 rectifier in the screen circuit, instead of a metal rectifier.

The valve anode and screen circuits are fed with a.c., the valve under examination being it's own rectifier.  The meter is a d.c. moving coil type.  The standing current is opposed by a backing off circuit, then a d.c. bias applied to the control grid, and mutual conductance read off the meter.

Filament voltage: 1.1 to 126 v. a.c.

Anode voltage: a.c. rectified by the valve under examination.  Equivalent to 0 to 400 v. d.c.

Screen voltage: a.c. rectified by the valve under examination.  Equivalent to 0 to 300 v. d.c.

Control grid voltage: 0 to -100 v. d.c. in 2 ranges.

Can test diode and rectifier emission.

Can measure inter-electrode leakage hot and cold.

The gas test switches a resistor in the control grid circuit to detect grid current.  The anode current being altered by the change of control grid bias thus developed across the resistor.

Here you find 82 models, 79 with images and 41 with schematics for wireless sets etc. In French: TSF for Télégraphie sans fil.
All listed radios etc. from AVO Ltd.; London