3 replies to this topic

[rmorein]

What is the active diameter of an 18mm tube?

 

I seem to recall 18mm is the exterior diameter.

[sixela]

Nope, that is indeed the photocathode/phosphor screen diameter.

Edited by sixela, 19 May 2025 - 03:54 PM.

[TOMDEY]

I'm pretty sure I checked that once long ago and got 18.0mm. It's consistent with the focal length, TFOV, and AFOV of 50^o. Checking some of my components here --- the GaAs measures at 20mm and the virtual phosphor screen at 18+mm physical diameters. So it sure seems that 18mm is indeed the true available field. That's the traditional common workhorse ~small ones~. The bigger ones are 25mm.   Tom

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[sixela]

On the Chinese NNVT tubes the useful photocathode diameter can be slightly smaller but it's listed on the spec sheet, and the minimum is 17.5 and it varies between that and 18.8 mm.