The Melles Griot model 05-LPM-371-065 will operate most 15 to 23 inch long HeNe tubes or heads.

Specifications:

Input: 10 to 14 VDC, 1.7 to 2.5 Amps. 25 Watts max
Output: 2500 to 3500 VDC, 5.8 to 8.0mA, user adjustable (preset @ 6.5mA)
Start voltage:  >10KV
Dimensions:  4.9″ x 3.3″ x 1.2″ (125 x 84 x 30mm)

Features:

4 second Turn-on delay (defeat by cutting violet wire loop)
TTL turn-on (yellow wire to ground=ON)
Alden high voltage output connector.