Electrometer triodes are specially designed to have grid current about six orders of magnitude less than typical triodes, this one has a grid current around 0.1 pico Amperes. They were used in pH meters, DC milli- and micro-voltmeters, ammeters with full scale deflections as low as 10 picoamps, and other applications where very high input impedance was required. These are the FET input opamps of the thermionic age. These valves should be operated in total darkness to obtain full rated performance. The example shown was made by Mullard at the Mitcham factory (indicated by the trailing 'D' below the CV number) but there is no etched code ( 2Y) on the envelope.
This valve has a special B5J/F wire ended base, designed for direct soldering. The 'NC' wire is cut off close to the envelope. The red spot is adjacent to the anode connection.
| Vf | If | Va | Ia | Vg | gm | μ | Ig |
| (V) | (mA) | (V) | (μA) | (V) | (μA/V) |
|
(A) |
| 1.25 | 13 | 9 | 100 | -2.5 | 80 | 1.7 | <12.5x10-14 |
The later Mullard "Industrial valves and tubes - Quick Reference", 1969/70, gives a value for μ of 2.0. All other values are the same. Note the very low anode voltage of 9 volts.
Reference
"Electrometer Valves", S.S. Dagpunar, Mullard Technical Communications, Aug. 1963.