| 1st Letter |
Z |
| 1st figure |
Type of base - same code as Mullard receiving valve
code |
| 2nd and 3rd figures |
Serial number |
| 2nd letter |
A |
Amplifier tube (continuous operation) |
| B |
Binary counter or switching tube |
| C |
Multistage counter |
| E |
Electrometer trigger or amplifier tube |
| G |
Gating tube |
| M |
Indicator (metering) tube |
| S |
Multistage switching tube |
| T |
3-electrode trigger tube |
| U |
4-electrode trigger tube |
| W |
5-electrode trigger tube |
