29-12-2020, 08:54 AM
(This post was last modified: 29-12-2020, 08:56 AM by ppppenguin.)
I think Braun's earliest CRTs had a small amount of gas. I don't know if this was a help, a hindrance or simply the side effect of realtively poor vacuum pumps. I don't think any commercial TV, radar or scope tubes were deliberately gassy though happy to be proven wrong. This is unlike some very early (pre WW1) valves where the gas was essential.
In 1986 when I steered a pre-war EMI 6/6 through rebuild the picture was disappointingly soft when I first ran it in a set. After an hour or 2 it was superb. I had activated the cathode on a test rig beforehand but presumably not enough to bring it up to full emission.
Low velocity TV camera tubes (that's virtually all of them) suffer from helium ingress. Although the partial pressure of helium in the atmosphere is very low, this houdini of a gas can diffuse through glass into the vacuum of the tube. The result is degraded pictures as the helium atoms jostle the low velocity electrons. Not a problem in CRTs AFAIK since the high velocity electrons don't really care. And the glass is thicker than on a camera tube which makes it less permeable.
In 1986 when I steered a pre-war EMI 6/6 through rebuild the picture was disappointingly soft when I first ran it in a set. After an hour or 2 it was superb. I had activated the cathode on a test rig beforehand but presumably not enough to bring it up to full emission.
Low velocity TV camera tubes (that's virtually all of them) suffer from helium ingress. Although the partial pressure of helium in the atmosphere is very low, this houdini of a gas can diffuse through glass into the vacuum of the tube. The result is degraded pictures as the helium atoms jostle the low velocity electrons. Not a problem in CRTs AFAIK since the high velocity electrons don't really care. And the glass is thicker than on a camera tube which makes it less permeable.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
