BTH BT85 / CV381 hydrogen thyratron. The fly leads at the base are the heater, cathode tied to one, and the grid connection is via the strap round the glass.
Markings on the glass show a serial number S3682 and the makers (B.T.H. Co. Ltd. Rugby), as well as its CV381 number.
| Heater voltage | 2.5V |
| Heater current | 10 to 12A |
| Max peak anode voltage | 10kV |
| Max peak anode current | 90A |
| Max rate of rise of anode current | 1500A/µs |
| Max negative grid voltage | -100V |
| Max mean anode current | 100mA |
| Max PRF | 2500 pps |
A yellow bead indicates the heater lead, red bead is grid, and the heater/cathode connection is to the metal support bracket. Anode is the top cap.
