The Melles Griot model L08105-1 will operate most 15 to 21 inch long HeNe tubes or heads.
Hook up sheet included. These are used units, tested and working.

Specifications:

Input: 10.5 to 14 VDC, 1.7 to 2.2 Amp
Output: 2500 to 3100 VDC, 5.5 to 7.0mA, user adjustable (preset @ 6.5mA)
Start voltage:  >10KV
Dimensions:  4.75″ x 2.96″ x 1.25″ (121 x 75 x 32mm)

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.
RoHS compliant