| 1st letter |
X |
Tubes employing photosensitive
materials |
| Y |
Vacuum tubes for transmitting,
microwave or industrial applications |
| Z |
Gas filled tubes (except
those with photosensitive materials) |
| 2nd letter |
A |
Diode |
| C |
Trigger tube |
| D |
Triode (including double
triodes) |
| G |
Miscellaneous |
| H |
Traveling wave tube |
| J |
Magnetron |
| K |
Klystron |
| L |
Tetrode or pentode (including
double tetrodes or double pentodes) |
| M |
Cold cathode indicator
or counter tubes |
| P |
Photomultipliers or radiation
counters |
| Q |
Camera tube |
| T |
Thyratron |
| X |
Ignitron, image converter
or image intensifier |
| Y |
Rectifier |
| Z |
Voltage stabiliser |
| Figures
- the serial number always consists of 4 digits. Prototypes end
in 0. |
