| First number:
heater power |
1 |
0 (no heater, cold cathode
etc) |
| 2 |
Up to 10W |
| 3 |
>10W to 20W |
| 4 |
>20W to 50W |
| 5 |
>50W to 100W |
| 6 |
>100W to 200W |
| 7 |
>200W to 500W |
| 8 |
>500W to 1000W |
| 9 |
>1000W |
| Letter: device
type |
A |
Single element e.g. ballasts |
| B |
Diode, including protective
devices, spark gaps, TR cells etc. |
| C |
Triode |
| D |
Tetrode |
| E |
Pentode |
| F |
Hexode |
| G |
Heptode |
| H |
Octode |
| J |
Magnetically controlled
e.g. magnetron |
| K |
Electrostatically controlled
e.g. klystron |
| L |
Vacuum capacitors |
| N |
Crystal rectifiers, solid
state devices |
| P |
Photoemissive types, e.g.
photocells |
| Q |
Cavities |
| R |
Ignitrons etc. |
| S |
Vacuum switches |
| T |
Storage, radial beam and
other special control tubes |
| V |
Photoflash |
| W |
Travelling wave tubes |
| X |
X-ray tubes |
| Y |
Thermionic converters |
| Second number: serial |
Assigned sequentially
starting from 21. |
