Re: Some interesting Nuvistor information


I remember the statement that Xray becomes an issue in tubes only when they are operated above 15.000 volts. Did older and smaller CRTs operating on lower voltages use leaded glass or other Xray supression? I can't think of any Tektronix equipment that used over 12.000 volts, so was there any concern?

Bruce Gentry, KA2IVY

On 6/24/20 12:35 AM, Chuck Harris wrote:
I don't really want to get into this to any great extent on
tekscopes, as it is only extremely loosely connected in that
it involves... CRT's.

I designed equipment to help electronics recyclers safely dismantle
CRT's into the hazardous and non hazardous waste parts. The
faceplate could be landfilled, and often was. It was a cost effective
landfill cover.

The faceplate was thick because it was relatively flat, and couldn't
otherwise safely withstand the force of the atmospheric pressure on the
internal vacuum. It contained a little barium to keep xray emission
to within standards.

Lead wasn't used on the face of the CRT because lead glass fluoresces
in an xray stream. It glows a sickly yellow green, just like vaseline

The funnel section and the neck of CRTs are made out of leaded
glass that contains the same amount of lead as the very best Steuben
lead glass crystal ... about 25%.

The radioactive material used in neon lamps, hydrogen thyratrons, and
probably krytrons (I have no experience with them) is there to make
the strike voltage the same whether the device is in bright light, or
is shut up in a dark chassis. Gas ionization starts easier if there
is a little light, or a few gamma rays whizzing about.

-Chuck Harris

stevenhorii wrote:
Any of you ever see a hydrogen thyratron with a greenish glass top sealed
to the cap? Look up 4C35A as an example. That glass is uranium glass. It is
known to antique collectors as "Vaseline glass" because of its green color.
Yes, it is radioactive and yes, they made things designed to hold food out
of it. Collectible now. Because of this, there are imitation Vaseline glass
pieces out there. The infamous Krytron trigger tube (used at one time to
trigger nuclear weapons as the trigger time was very fast). They contained
a radioactive isotope of nickel. In both cases. the radioactivity keeps a
small volume of the gas ionized.

Later CRTs used in TVs had higher accelerating voltages for increased
brightness. Slam high energy electrons into something with a reasonably
high atomic number and you make x-rays (hmm-metal shadow mask in a color TV
tube?) So, the outer faceplates of those CRTs were made with leaded glass.
This is the major reason landfills stopped accepting tube TVs. When your
mother told you not to sit too close to the TV, there was a reason.

Does anyone know if oscilloscope tubes used a leaded faceplate?

Steve H

On Tue, Jun 23, 2020 at 9:03 PM Ray <@Ray3B5F5E> wrote:

Not to mention that there are tubes out there that had radioactive coated
cathodes for improved electron emissions. Sent from my T-Mobile 4G LTE
device------ Original message------From: Shirley Dulcey KE1LDate: Thu, Jun
18, 2020 21:01To:;Cc: Subject:Re: [TekScopes] Some
interesting Nuvistor informationBack then, any tubes in the TVs at the dump
would have gone straight to
landfill. (Nowadays some of them would require hazmat treatment because of
lead.) If you took out the tubes to use you were practicing one of the legs
of the Reduce, Reuse, Recycle slogan. If you were taking them out to break
them and listen to the glass shatter, shame on you, but those tubes would
have been lost to the world anyway.

On Thu, Jun 18, 2020 at 9:36 PM snapdiode via wrote:

Now I feel bad for cracking all those Compactrons when I was ten. I
them out of TVs at the city dump, which was pretty much unsupervised back
then. Slip under the fence, crack open the TVs, come home with backpack
full of tubes! About 1/3 of them were Compactrons.

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