One of my 561's has a severely double-peaking CRT and it's not that bright. Voltages are in spec. It's probably not worth locating and buying a new CRT (especially if the USPS is going to handle the package the way they did my more recent small packages)! Since it will only see relatively few hours, I'm thinking about trying a quickie rejuvenation like this:
http://www.ke5fx.com/crt.html

I did it successfully 10 years ago on an old arcade color monitor which I only used occasionally (not 16 hrs a day in an arcade) which is noted in the comments of that article. But I sold the game before I found out how many more hours it would add to the heater life.

Thoughts?

As a tidbit of trivia and only a little bit off topic.

Eimac tried to build, I think it 8877's, at their plant in Salt Lake City with not much success. They determined that the "air in SLC was different than in San Carlos, CA and the cathodes were getting poisoned.

There seems to be a fair bit of magic in making tubes work properly

Steve

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Roy Thistle
Sent: Monday, March 8, 2021 11:40 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Restoring CRT emission?

Hi Charles:
I read through a two decades old PHd thesis on CRT cathodes. ( as anyone can too! There are any number of people posting here who will first humiliate one.. but, explain things one might not understand.) I also read through the "B&K 467 Cathode Ray Tube Restorer Analyser" manual. (There's even a nifty picture of Karl Corn inside the front cover... yes, those were the days!) In my opinion, people working with CRTs in the field (TV repairmen, video game repairmen) contributed to forming a model that was sufficient to explain a methodology... so that engineers (at B&K, Sencore and others) could design and build things like the 467. But to my knowledge the "model" that was used, by those designers, was never sufficiently explained scientifically. And the thesis referred to above offers several competing models: about what happens as CRT cathodes/filaments age, degrade, or become poisoned.
Just the same, I've seen several topics and posts ..,here on TekScopes ... about, "welding filaments", rejuvenating/brightening/rebuilding, old oscilloscope CRTs.
As far as I cant tell, a lot of what is reported on the Internet, about "rejuvenating" CRTs ... regarding "how rejuvenation works" and "whether it works" is foolishness.
Yes! TV repairmen did "rejuvenate/brighten" TV CRTs (using self devised methods, or gear like the 467); but, the old-timers that I knew ... they related that it was a temporary strategy. It allowed them to "rejuvenate" the CRT, on site, while they ordered in a new (or rebuilt) CRT. Rejuvenation didn't last very long!
There might be something different about the CRTs Tektronix used (and made) that might allow "rejuvenation."
But bear in mind that as far as I can tell, no CRT was designed to reliably withstand the peak pulse power (or the relatively large average current/voltages) that rejuvenation gear (or home-brew hacks) apply between the cathode and grid (or to the filament).
Best regards.



--
Roy Thistle

I found this online - a reprint of an article apparently from
Antiqueradios.com on rejuvenating vacuum tubes. There is a fair bit of
discussion on cathodes and their emitting surfaces.

https://antiqueradios.com/chrs/journal/rejuvenation.html

A bit of a concern to me regards the use of thorium as a cathode emitter.
Some caution might be advised if scrapping (by that I mean breaking) old
non-working vacuum tubes (I know - considered a sin amongst tube
collectors). Thorium is radioactive and its decay products include radon.
The article mentions transmitting tubes which are usually high power tubes
that would not likely be in an oscilloscope (?)

I did research the old TV "tube brighteners" and apparently what they did
was to boost the filament voltage. One description of them (one of them on
eBay) does mention that some TV repair places had equipment that did more
than this (maybe that B&K 467?)

Anyway, I thought the discussion in this article might be useful for this
thread.

Steve Horii

On Mon, Mar 8, 2021 at 2:40 PM Roy Thistle <roy.thistle@mail.utoronto.ca>
wrote:

Hi Charles:
I read through a two decades old PHd thesis on CRT cathodes. ( as anyone
can too! There are any number of people posting here who will first
humiliate one.. but, explain things one might not understand.)
I also read through the "B&K 467 Cathode Ray Tube Restorer Analyser"
manual. (There's even a nifty picture of Karl Corn inside the front
cover... yes, those were the days!)
In my opinion, people working with CRTs in the field (TV repairmen, video
game repairmen) contributed to forming a model that was sufficient to
explain a methodology... so that engineers (at B&K, Sencore and others)
could design and build things like the 467. But to my knowledge the "model"
that was used, by those designers, was never sufficiently explained
scientifically. And the thesis referred to above offers several competing
models: about what happens as CRT cathodes/filaments age, degrade, or
become poisoned.
Just the same, I've seen several topics and posts ..,here on TekScopes ...
about, "welding filaments", rejuvenating/brightening/rebuilding, old
oscilloscope CRTs.
As far as I cant tell, a lot of what is reported on the Internet, about
"rejuvenating" CRTs ... regarding "how rejuvenation works" and "whether it
works" is foolishness.
Yes! TV repairmen did "rejuvenate/brighten" TV CRTs (using self devised
methods, or gear like the 467); but, the old-timers that I knew ... they
related that it was a temporary strategy. It allowed them to "rejuvenate"
the CRT, on site, while they ordered in a new (or rebuilt) CRT.
Rejuvenation didn't last very long!
There might be something different about the CRTs Tektronix used (and
made) that might allow "rejuvenation."
But bear in mind that as far as I can tell, no CRT was designed to
reliably withstand the peak pulse power (or the relatively large average
current/voltages) that rejuvenation gear (or home-brew hacks) apply between
the cathode and grid (or to the filament).
Best regards.




--
Roy Thistle

On Mar 8, 2021, at 2:59 PM, Chuck Harris <cfharris@erols.com> wrote:

There is more radioactive thorium in a coleman gas lantern mantle
than is in a transmitter cathode. Typically, the thorium in
a cathode is alloyed in the tungsten filament to make it emit
electrons at a lower temperature.

Unwarranted fright over thorium in vacuum tubes caused DRMO to
remove vacuum tubes from radios and test equipment, and toss them
in steel barrels... breaking them, rather than sell them to the
public...

-Chuck Harris

stevenhorii wrote:

I found this online - a reprint of an article apparently from
Antiqueradios.com on rejuvenating vacuum tubes. There is a fair bit of
discussion on cathodes and their emitting surfaces.

https://antiqueradios.com/chrs/journal/rejuvenation.html

A bit of a concern to me regards the use of thorium as a cathode emitter.
Some caution might be advised if scrapping (by that I mean breaking) old
non-working vacuum tubes (I know - considered a sin amongst tube
collectors). Thorium is radioactive and its decay products include radon.
The article mentions transmitting tubes which are usually high power tubes
that would not likely be in an oscilloscope (?)

I did research the old TV "tube brighteners" and apparently what they did
was to boost the filament voltage. One description of them (one of them on
eBay) does mention that some TV repair places had equipment that did more
than this (maybe that B&K 467?)

Anyway, I thought the discussion in this article might be useful for this
thread.

Steve Horii

On Mon, Mar 8, 2021 at 2:40 PM Roy Thistle <roy.thistle@mail.utoronto.ca>
wrote:

Hi Charles:
I read through a two decades old PHd thesis on CRT cathodes. ( as anyone
can too! There are any number of people posting here who will first
humiliate one.. but, explain things one might not understand.)
I also read through the "B&K 467 Cathode Ray Tube Restorer Analyser"
manual. (There's even a nifty picture of Karl Corn inside the front
cover... yes, those were the days!)
In my opinion, people working with CRTs in the field (TV repairmen, video
game repairmen) contributed to forming a model that was sufficient to
explain a methodology... so that engineers (at B&K, Sencore and others)
could design and build things like the 467. But to my knowledge the "model"
that was used, by those designers, was never sufficiently explained
scientifically. And the thesis referred to above offers several competing
models: about what happens as CRT cathodes/filaments age, degrade, or
become poisoned.
Just the same, I've seen several topics and posts ..,here on TekScopes ...
about, "welding filaments", rejuvenating/brightening/rebuilding, old
oscilloscope CRTs.
As far as I cant tell, a lot of what is reported on the Internet, about
"rejuvenating" CRTs ... regarding "how rejuvenation works" and "whether it
works" is foolishness.
Yes! TV repairmen did "rejuvenate/brighten" TV CRTs (using self devised
methods, or gear like the 467); but, the old-timers that I knew ... they
related that it was a temporary strategy. It allowed them to "rejuvenate"
the CRT, on site, while they ordered in a new (or rebuilt) CRT.
Rejuvenation didn't last very long!
There might be something different about the CRTs Tektronix used (and
made) that might allow "rejuvenation."
But bear in mind that as far as I can tell, no CRT was designed to
reliably withstand the peak pulse power (or the relatively large average
current/voltages) that rejuvenation gear (or home-brew hacks) apply between
the cathode and grid (or to the filament).
Best regards.




--
Roy Thistle

There is more radioactive thorium in a coleman gas lantern mantle
than is in a transmitter cathode. Typically, the thorium in
a cathode is alloyed in the tungsten filament to make it emit
electrons at a lower temperature.

Unwarranted fright over thorium in vacuum tubes caused DRMO to
remove vacuum tubes from radios and test equipment, and toss them
in steel barrels... breaking them, rather than sell them to the
public...

-Chuck Harris

stevenhorii wrote:

I found this online - a reprint of an article apparently from
Antiqueradios.com on rejuvenating vacuum tubes. There is a fair bit of
discussion on cathodes and their emitting surfaces.

https://antiqueradios.com/chrs/journal/rejuvenation.html

A bit of a concern to me regards the use of thorium as a cathode emitter.
Some caution might be advised if scrapping (by that I mean breaking) old
non-working vacuum tubes (I know - considered a sin amongst tube
collectors). Thorium is radioactive and its decay products include radon.
The article mentions transmitting tubes which are usually high power

tubes

that would not likely be in an oscilloscope (?)

I did research the old TV "tube brighteners" and apparently what they did
was to boost the filament voltage. One description of them (one of them

on

eBay) does mention that some TV repair places had equipment that did more
than this (maybe that B&K 467?)

Anyway, I thought the discussion in this article might be useful for this
thread.

Steve Horii

On Mon, Mar 8, 2021 at 2:40 PM Roy Thistle <roy.thistle@mail.utoronto.ca

wrote:

Hi Charles:
I read through a two decades old PHd thesis on CRT cathodes. ( as anyone
can too! There are any number of people posting here who will first
humiliate one.. but, explain things one might not understand.)
I also read through the "B&K 467 Cathode Ray Tube Restorer Analyser"
manual. (There's even a nifty picture of Karl Corn inside the front
cover... yes, those were the days!)
In my opinion, people working with CRTs in the field (TV repairmen,

video

game repairmen) contributed to forming a model that was sufficient to
explain a methodology... so that engineers (at B&K, Sencore and others)
could design and build things like the 467. But to my knowledge the

"model"

that was used, by those designers, was never sufficiently explained
scientifically. And the thesis referred to above offers several

competing

models: about what happens as CRT cathodes/filaments age, degrade, or
become poisoned.
Just the same, I've seen several topics and posts ..,here on TekScopes

...

about, "welding filaments", rejuvenating/brightening/rebuilding, old
oscilloscope CRTs.
As far as I cant tell, a lot of what is reported on the Internet, about
"rejuvenating" CRTs ... regarding "how rejuvenation works" and "whether

it

works" is foolishness.
Yes! TV repairmen did "rejuvenate/brighten" TV CRTs (using self devised
methods, or gear like the 467); but, the old-timers that I knew ... they
related that it was a temporary strategy. It allowed them to

"rejuvenate"

the CRT, on site, while they ordered in a new (or rebuilt) CRT.
Rejuvenation didn't last very long!
There might be something different about the CRTs Tektronix used (and
made) that might allow "rejuvenation."
But bear in mind that as far as I can tell, no CRT was designed to
reliably withstand the peak pulse power (or the relatively large average
current/voltages) that rejuvenation gear (or home-brew hacks) apply

between

the cathode and grid (or to the filament).
Best regards.




--
Roy Thistle

Chuck is absolutely right. The amount of thorium in a cathode is vanishingly small — it is used to lower the work function at the surface of the tungsten, and is typically present in concentrations measured below tenths of a percent, if memory serves.

It is relevant to note that tungsten cathodes are not used in CRTs (nor in modern receiving tubes). Those, as far as I know, are all indirectly heated. No thorium. They use cathodes of barium/strontium oxide.

Lantern mantles of old were full of thorium. Those were great for testing Geiger counters. Modern mantles are thorium free. I did not know this until I told a friend he could test his ionization detector with a mantle. He was disappointed.

—Tom

Unbroken, the vacuum tubes with thoriated cathodes would not be a problem.
The government made things worse by having them smashed. But the government
also sold off Bomarc Missile surplus years ago without warning that the
structural parts were thoriated magnesium. A scrap metal dealer supposedly
died after cutting the missile chassis apart with a grinder. However,
though I heard this story from a couple of scrap metal dealers, one also
mentioned that he was also a heavy smoker so any inhaled thoriated
magnesium dust or radon was not likely the main cause of his undoing.

WW II aircraft instruments with radium-painted dials were also sold off as
surplus. Many of the WW II sextants also had radium paint around the bubble
chambers for a "backup" if the electric illumination failed. These sextants
and aircraft instruments still turn up. People make the mistake of thinking
that if the instrument face does not glow in the dark that it is safe. It
is not. The radium is still plenty radioactive - the phosphor mixed with it
quits glowing (oxidation?) I buy a lot of surplus electronics and I keep a
survey meter around to check things.

Ionization smoke detectors have small amounts of 241Americium, but about 1
microcurie. Not particularly hazardous and they can apparently either be
simply thrown in the trash or (if your county has one) a disposal facility.
So far as I know, they are not handled like radioactive waste.

I don't know of any radiation hazard from Tek scopes. I suspect that any
x-rays produced by the beam and the faceplates are minimal.

Steve Horii

On 09 March 2021 at 18:11 stevenhorii <sonodocsch@gmail.com> wrote:


Thoriated magnesium was even used in the Apollo program. The frames of the
computers (CM and LM) and some of the other electronics were made using it.
NASA did a study of the radiation from these components and determined that
given the duration of the lunar missions, it would not be a risk. The
radiation exposure from the Van Allen belts would be higher. NASA designed
the trajectories to minimize time passing through the belts and to pass
through (or near) the less energetic area of them. I was visiting the
Kansas Cosmosphere when they received a Titan I for their collection. It
was in segments. The body segments were all stamped with "Thoriated
magnesium" so the government determined at some point to warn people.

Beryllium is very interesting stuff. Again, the Apollo spacecraft used a
lot of it. Most of the structure of the optical assemblies (sextant and
telescope in the CM, alignment telescope in the LM) were made of beryllium
because of the light weight and high rigidity. The inertial measurement
unit had a beryllium stable member into which the gyros and accelerometers
were bolted. The mirrors in the sextant and LM telescope were also made of
beryllium. It was nickel plated, then aluminized for the reflective
surfaces. A company called Speedring made most of these parts - they had
the facility to machine beryllium without causing berylliosis among the
workers (or the people in neighboring areas!)

Beryllium is not toxic in the same way that say, arsenic is toxic. What it
does is to cause a severe allergic reaction in the lungs which leads to
severe chronic lung disease. If enough dust is breathed in, there is a form
of acute beryllium toxicity which produces a chemical pneumonia. If you get
a sliver of beryllium, you develop a localized allergic reaction to it. So
it is poisonous in the sense that it will kill you but not like cyanide or
other toxins that immediately affect your metabolism.

I don't know when they started making beryllium oxide parts pink, but the
manufacturers did. The early BeO parts were white and looked like aluminum
oxide. Dust from those would also be toxic. I once contacted a surplus
seller because they had insulators listed in their catalog. The photo
showed them to be pink and they were designed as heat conductor/insulators
for high-power transistors. I warned them that these were made of BeO and
at the least, they should warn purchasers about them. They pulled them from
the catalog. I also was in a scrap yard and they had these huge tubes -
maybe 12 feet long and 6 inches in diameter - that were all white ceramic.
They had a tag that said they were beryllium oxide. I've no idea what they
were for. I'd never seen any BeO parts that large. I warned the surplus
dealer about them - he didn't know. But he knew of someone who would buy
them as beryllium scrap so he did not do his usual thing with stuff he
could not identify and smash or cut it up.

I don't recall seeing any BeO insulators in Tek stuff. I think there were
some silicone ones or in early stuff, mica ones. I am pretty sure that the
500-series scopes with the ceramic terminal strips used aluminum oxide or
porcelain for them. Maybe someone in this group knows. I doubt they were
beryllium oxide.

As a radiologist, I've seen chest x-rays of people with berylliosis and
also asbestosis. The Philadelphia Navy Yard had a lot of people exposed to
asbestos and there were a couple of aerospace companies that used beryllium
parts, but I don't know that they machined the parts in-house. Both are
very nasty diseases.

Steve Horii





On Mon, Mar 8, 2021 at 7:45 PM Ed Breya via groups.io <edbreya=
yahoo.com@groups.io> wrote:

Steve, you may be thinking of beryllium alloyed with magnesium. Many
structural and precision mechanical parts were made with Be in the old
days, for light weight and strength. Be particles can be highly toxic if
inhaled. Same with things containing it, like the alloys and BeO ceramics.
It's still used today, but only where essential, like Be X-ray tube windows
(transparent), and BeO for very high thermal conductivity - although newer,
better, less toxic things have emerged, offering more choices in critical
thermal applications. If you have any microwave gear, you may find it
interesting that the tiny YIG spheres in YTOs and such, are typically
mounted on tiny BeO rods.

As far as I recall, the only things in electronics with thorium are
thoriated-tungsten in high power and other special tubes, and TIG welding
electrodes. The old lantern mantles with Th do indeed make handy sources,
but need proper safe handling.

I think the common indirectly heated tubes we normally see use a nickel
cathode sleeve with zirconia and maybe barium coating. The tungsten heater
wire inside is similarly coated for insulation, but also forms a rectifier
from it to the cathode, so the H-K bias voltage and leakage is a
consideration for operation.

Ed

On Mar 8, 2021, at 10:05 PM, Ed Breya via groups.io <edbreya=yahoo.com@groups.io> wrote:

Steve said: "Thoriated magnesium was even used in the Apollo program..."

Huh, I have never heard of that before. What did thoriating do for the Mg?

Ed