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Andrews Rapid Here’s one to think about. I wanted to take a quick picture of this cold cathode Crookes tube operating and to check the vacuum condition. This tube is likely to date somewhere between 1915 -1930. Cold cathode tubes of this type have imperfect vacuum and the gas pressure, or vacuum hardness, is controlled by passing a current through a small reservoir made with mica covered electrodes attached at the top of the tube. I’ve done something wrong here, any ideas? I’ve shown an image of it off and operating to help. Keywords: Miscellaneous

Andrews Rapid


Here’s one to think about. I wanted to take a quick picture of this cold cathode Crookes tube operating and to check the vacuum condition. This tube is likely to date somewhere between 1915 -1930. Cold cathode tubes of this type have imperfect vacuum and the gas pressure, or vacuum hardness, is controlled by passing a current through a small reservoir made with mica covered electrodes attached at the top of the tube. I’ve done something wrong here, any ideas? I’ve shown an image of it off and operating to help.

crookes.jpg laser_co2.jpg Copper-K~0.jpg puddle_flash.jpg nixi.jpg
Lamp/Fixture Information
Manufacturer:Cuthbert Andrews
Physical/Production
Factory Location:England
Application/Use:medical
File information
Filename:crookes.jpg
Album name:Tuopeek / Misc
Keywords:Miscellaneous
Filesize:694 KiB
Date added:10 Feb 2026
Dimensions:2500 x 2844 pixels
Displayed:12 times
DateTime Original:2026:02:09 21:20:49
Exposure Time:1 sec
FNumber:f/4
File Source:Digital Still Camera
Flash:No Flash
Focal length:26 mm
ISO:1600
Model:NIKON D3400
Software:Adobe Photoshop Elements 2.0
White Balance:0
URL:https://trad-lighting.net/gallery/displayimage.php?pid=1108
Favourites:Add to Favourites

Comment 1 to 4 of 4
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Sammi   [Wed 11 Feb 2026 at 01:08]
Ermm... Over to you Max.! Mind Blown
Max   [Thu 12 Feb 2026 at 07:20]
Interesting picture and peculiar luminescence pattern! About your question: isn't the left electrode supposed to be operated as a cathode only? Here we can see the (faint) electron projection from the central (tilted) electrode towards the glass bulb, which is certainly not supposed to happen under normal conditions. At what voltage did you run it?
Tuopeek   [Thu 12 Feb 2026 at 11:17]
Well spotted Max, I think your pretty much on the money there. The left electrode IS supposed to be the cathode only. In my haste, I have connected the tube in reverse bias. In the 'off' picture you can see the heavy insulated wire, which is positive, connected to the wrong side. I was wanting to grab a very quick picture and didn't take note of the voltage as its from a variable HV supply. Just turned it up and remotely grabbed the picture when emission started. Even with the gas regulator operated for a short time this tube will not start to conduct until close to 30kV so I am guessing it will be just above 30kV here.
Sammi   [Fri 13 Feb 2026 at 18:14]
I knew that we could count on Max for coming up with the answer.! Very Happy

Comment 1 to 4 of 4
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