A 6914 is known as a Gen 0 image tube because it has no gain and converts shortwave IR to visible light. The photocathode is an S1 type and the screen a P31, both are 25mm indiameter. This tube requires about 15,000 volts at a few micro-amps for operation.

We produce the Gen 2 night vision intensifier tubes to replace  6914 Varo Infrared Night Vision Image Intensifier Tube,Gen 2, Inverted, Non autogated, 25 mm input and 25 mm output diameter, similar tube dimensions with Gen 0 Varo 6914 see the below physical picture,parameter and drawing: