boiling off electrons

[John Larkin]

On Sun, 25 Jan 2009 18:38:01 -0800, Don Kelly <dhky@shawcross.ca>
wrote:

John Larkin wrote:
On Wed, 21 Jan 2009 21:57:01 -0800 (PST), RichD
r_delaney2001@yahoo.com> wrote:


I don't know much about vacuum tubes, but often
I have read statements like "the cathode heats up,
causing electrons to boil off and fly to the anode"..
which makes me scratch my head..

How does an electron boil? Can anyone explain this?


Electrons in a metal or similar are bound by bonding forces. As you
heat things up, some electrons acquire more energy and, if near the
surface, may break away. The energy is called the "work potential",
measured in volts (or electron-volts.) Once free of the surface, any
extra energy past the escape potential gives the electron some
velocity.


Are there degrees of boiling, like a pot of water,
or is there an on/off threshold?


Below some critical temperature, there's insufficient energy to
escape. Above that, electron emission goes up fast as temp rises.


Then there's the grid mask, whatever that is... how
come the electrons don't smash into that? How do
they find the holes?


It's a very sparse grid of wires, so most electrons miss, just drift
through the big holes between the tiny wires. If you apply a high
negative voltage, you can force the electrons further from the wires,
crowd them into the gaps betweem, and eventually shut down the gaps
completely.

Is this like synchronized diving,

they're trained to hit the water at specified spots?


They are random and unsynchronized, although they do repel one
another, which adds a certain sort of order.

John


In other words, a high negative potential at the grid wires produces a
local field that is negative with respect to the cathode- counteracting
the field due to the anode. Do we have "holes" between wires? Not
really- but it is a nice way to visualize (visualise outside the US) it
without messy field analysis-even if it is not true..

There certainly are holes between the grid wires. How else can
electrons sneak past when the grid is, say, -20 volts? If the grid
array were a perfect Farady shield, no electrons could get through.

The positive plate potential sort of reaches between the grid wires
and projects fingers of positive potential towards the cathode,
allowing electrons to be sucked through.

If you move the grid wires closer together, a negative grid bias would
be more effective in reducing plate current; the cathode would
essentially see a better far-field Farady shield. Variable-mu tubes
had a nonuniform grid spacing so that the transfer characteristic had
a long tail... the close-spaced part of the grid cut off at a lower
negative voltage than the wide-spaced part. Wider holes.

Yes, you'd have to do a proper field analysis to see what's going on
in a more precise way.

John

 

[BradGuth]

On Jan 24, 4:57 pm, Salmon Egg <Salmon...@sbcglobal.net> wrote:

In article
ed70c17b-6435-4945-ac24-dfe5ec853...@w39g2000prb.googlegroups.com>,

 BradGuth <bradg...@gmail.com> wrote:
Thanks for that Alpha/Beta reminder.  Radium, though mostly Alpha can
be made to produce its fair share Beta.

HOW? please be more specific. Thermionic emission is NOT beta emission
even though betas are electrons.



Radium is a whole lot safer than many other elements and known lethal
chemicals, and it's clearly a use it or lose it kind of element.
Unlike the longer lasting thorium or even uranium, it seems radium is
also one of the most privately horded and extremely valued elements on
Earth.

Please explain this as well. While alphas will not penetrate skin,
ingestion of radium has killed many people. Have you heard the story of
women who used to paint radium dials? Alphas emitted internally can be
very damaging because alphas ionize strongly and there is no skin to
protect sensitive tissue. With all the isotopes now available from
nuclear reactors and neutron irradiators, radium is too expensive and
unnecessary for wide application.

Bill

--
Private Profit; Public Poop! Avoid collateral windfall!

Good grief, a small amount of a radium cathode and of its radon gas in
a sealed tube is relatively safe as a smoke alarm, if not safer.

~ BG

 

[Jasen Betts]

On 2009-01-26, BradGuth <bradguth@gmail.com> wrote:

On Jan 24, 4:57 pm, Salmon Egg <Salmon...@sbcglobal.net> wrote:
In article
ed70c17b-6435-4945-ac24-dfe5ec853...@w39g2000prb.googlegroups.com>,

 BradGuth <bradg...@gmail.com> wrote:
Thanks for that Alpha/Beta reminder.  Radium, though mostly Alpha can
be made to produce its fair share Beta.

HOW? please be more specific. Thermionic emission is NOT beta emission
even though betas are electrons.



Radium is a whole lot safer than many other elements and known lethal
chemicals, and it's clearly a use it or lose it kind of element.
Unlike the longer lasting thorium or even uranium, it seems radium is
also one of the most privately horded and extremely valued elements on
Earth.

Please explain this as well. While alphas will not penetrate skin,
ingestion of radium has killed many people. Have you heard the story of
women who used to paint radium dials? Alphas emitted internally can be
very damaging because alphas ionize strongly and there is no skin to
protect sensitive tissue. With all the isotopes now available from
nuclear reactors and neutron irradiators, radium is too expensive and
unnecessary for wide application.

Bill

--
Private Profit; Public Poop! Avoid collateral windfall!

Good grief, a small amount of a radium cathode and of its radon gas in
a sealed tube is relatively safe as a smoke alarm, if not safer.

but then it's no longer a vacuum tube.

 

[John Larkin]

On Sun, 25 Jan 2009 22:18:56 -0800 (PST), BradGuth
<bradguth@gmail.com> wrote:

On Jan 24, 4:57 pm, Salmon Egg <Salmon...@sbcglobal.net> wrote:
In article
ed70c17b-6435-4945-ac24-dfe5ec853...@w39g2000prb.googlegroups.com>,

 BradGuth <bradg...@gmail.com> wrote:
Thanks for that Alpha/Beta reminder.  Radium, though mostly Alpha can
be made to produce its fair share Beta.

HOW? please be more specific. Thermionic emission is NOT beta emission
even though betas are electrons.



Radium is a whole lot safer than many other elements and known lethal
chemicals, and it's clearly a use it or lose it kind of element.
Unlike the longer lasting thorium or even uranium, it seems radium is
also one of the most privately horded and extremely valued elements on
Earth.

Please explain this as well. While alphas will not penetrate skin,
ingestion of radium has killed many people. Have you heard the story of
women who used to paint radium dials? Alphas emitted internally can be
very damaging because alphas ionize strongly and there is no skin to
protect sensitive tissue. With all the isotopes now available from
nuclear reactors and neutron irradiators, radium is too expensive and
unnecessary for wide application.

Bill

--
Private Profit; Public Poop! Avoid collateral windfall!

Good grief, a small amount of a radium cathode and of its radon gas in
a sealed tube is relatively safe as a smoke alarm, if not safer.

~ BG

Ionization smoke alarms use amerecium, and it's not sealed.

Photoelectric smoke alarms don't use radiation at all.

John

 

[Salmon Egg]

In article
<d2ed5726-691e-481e-94d6-a5745039d690@f40g2000pri.googlegroups.com>,
BradGuth <bradguth@gmail.com> wrote:

Good grief, a small amount of a radium cathode and of its radon gas in
a sealed tube is relatively safe as a smoke alarm, if not safer.

While strictly speaking this statement is not wrong, what does it have
to do with thermionic cathodes? It sounds like you are describing an
ionization chamber not a thermionic tube. The half life of any radon
isotope is rather short. What is the vapor pressure of the radon? Does
the radon serve as a plasma generator as does mercury vapor or noble
gas in a thyratron? Do you really understand tubes of various kinds?

Bill

--
Private Profit; Public Poop! Avoid collateral windfall!

 

[Salmon Egg]

In article <glk114$gh8$1@reversiblemaps.ath.cx>,
Jasen Betts <jasen@xnet.co.nz> wrote:

Good grief, a small amount of a radium cathode and of its radon gas in
a sealed tube is relatively safe as a smoke alarm, if not safer.

but then it's no longer a vacuum tube.

While not defending the statement, vacuum tube technology seems to
encompass tubes that strictly speaking are not vacuum tubes. In fact,
even vacuum tubes have lots of residual gas left over compared to what
modern technology can achieve.

Many gas filled tubes are still considered to be "vacuum tubes." These
include thyratrons and ignitrons, and proportional counters and Geiger
counters. Many of these tubes have cathodes. The ionized gas plasma is
used to reduce space charge effects so that higher currents can flow for
a given anode potential, This plasma reduces plate (anode) dissipation
and consequent efficieency.

Bill

--
Private Profit; Public Poop! Avoid collateral windfall!

 

[Rich Grise]

On Sat, 24 Jan 2009 12:08:36 -0600, Tim Wescott wrote:

It can't be done on just any tube (and no, I don't know enough to know
which ones it can or can't be done on), and if the grid ever gets hot
enough to start emitting electrons on its own it'll go positive and the
tube will run away and (probably) toast itself, so it can't be done _at
all_ on power tubes.

When I was in USAF electronics tech school, somebody would always send
some newbie off in search of "a can of grid-leak bias". ;-)

(also 20 feet of flight line, a bucket of prop wash, and a buffer
amplifier (when you're buffing the floor).)

Cheers!
Rich

 

[Benj]

On Jan 26, 4:35 pm, Rich Grise <r...@example.net> wrote:

When I was in USAF electronics tech school, somebody would always send
some newbie off in search of "a can of grid-leak bias". ;-)

(also 20 feet of flight line, a bucket of prop wash, and a buffer
amplifier (when you're buffing the floor).)

Heh. Yeah newbies always get it. When I was a newbie at the Chemistry
Dept. instrument repair shop, the standard thing was to "tygonize"
them. What you'd do is get a nice length of tygon tubing and a large
cigar. Then when one day when the unsuspecting newbie has some hyper-
expensive piece of gear on his bench he's fixing, you surreptitiously
snake the tubing into the instrument and when the newbie thinks he's
got it fixed and flips the power on, from around the corner you light
the cigar and blow smoke into the machine which then pours out of it
like it's on fire! Much fun then ensues as newbie panics! Yeah,
they got me that way too.

 

[Michael A. Terrell]

Benj wrote:

On Jan 26, 4:35 pm, Rich Grise <r...@example.net> wrote:

When I was in USAF electronics tech school, somebody would always send
some newbie off in search of "a can of grid-leak bias". ;-)

(also 20 feet of flight line, a bucket of prop wash, and a buffer
amplifier (when you're buffing the floor).)

Heh. Yeah newbies always get it. When I was a newbie at the Chemistry
Dept. instrument repair shop, the standard thing was to "tygonize"
them. What you'd do is get a nice length of tygon tubing and a large
cigar. Then when one day when the unsuspecting newbie has some hyper-
expensive piece of gear on his bench he's fixing, you surreptitiously
snake the tubing into the instrument and when the newbie thinks he's
got it fixed and flips the power on, from around the corner you light
the cigar and blow smoke into the machine which then pours out of it
like it's on fire! Much fun then ensues as newbie panics! Yeah,
they got me that way too.

I would have dropped the asshole with a bench stool before he could
get away from my bench. OTOH, my bench was usually out in the open,
away from any wall, and had space to walk all the way around it so your
childish stunt would be quite obvious. I had three benches at my last
job, along with a lot of equipment cats and a 4' * 8' table for
schematics. I was working on 80,000 telemetry receivers. The only way
to pull your stunt would be to drill a hole in the bench, and try to
hide the hose.


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[Tim Wescott]

On Fri, 30 Jan 2009 14:03:25 -0500, Michael A. Terrell wrote:

Benj wrote:

On Jan 26, 4:35 pm, Rich Grise <r...@example.net> wrote:

When I was in USAF electronics tech school, somebody would always
send some newbie off in search of "a can of grid-leak bias". ;-)

(also 20 feet of flight line, a bucket of prop wash, and a buffer
amplifier (when you're buffing the floor).)

Heh. Yeah newbies always get it. When I was a newbie at the Chemistry
Dept. instrument repair shop, the standard thing was to "tygonize"
them. What you'd do is get a nice length of tygon tubing and a large
cigar. Then when one day when the unsuspecting newbie has some hyper-
expensive piece of gear on his bench he's fixing, you surreptitiously
snake the tubing into the instrument and when the newbie thinks he's
got it fixed and flips the power on, from around the corner you light
the cigar and blow smoke into the machine which then pours out of it
like it's on fire! Much fun then ensues as newbie panics! Yeah,
they got me that way too.


I would have dropped the asshole with a bench stool before he could
get away from my bench. OTOH, my bench was usually out in the open,
away from any wall, and had space to walk all the way around it so your
childish stunt would be quite obvious. I had three benches at my last
job, along with a lot of equipment cats and a 4' * 8' table for
schematics. I was working on 80,000 telemetry receivers. The only way
to pull your stunt would be to drill a hole in the bench, and try to
hide the hose.

I'll keep that in mind if I ever hire you.

(note to self: use hollow floor)
(note to self: stay out of stool range)



--
http://www.wescottdesign.com

 

[Michael A. Terrell]

Tim Wescott wrote:

On Fri, 30 Jan 2009 14:03:25 -0500, Michael A. Terrell wrote:

Benj wrote:

On Jan 26, 4:35 pm, Rich Grise <r...@example.net> wrote:

When I was in USAF electronics tech school, somebody would always
send some newbie off in search of "a can of grid-leak bias". ;-)

(also 20 feet of flight line, a bucket of prop wash, and a buffer
amplifier (when you're buffing the floor).)

Heh. Yeah newbies always get it. When I was a newbie at the Chemistry
Dept. instrument repair shop, the standard thing was to "tygonize"
them. What you'd do is get a nice length of tygon tubing and a large
cigar. Then when one day when the unsuspecting newbie has some hyper-
expensive piece of gear on his bench he's fixing, you surreptitiously
snake the tubing into the instrument and when the newbie thinks he's
got it fixed and flips the power on, from around the corner you light
the cigar and blow smoke into the machine which then pours out of it
like it's on fire! Much fun then ensues as newbie panics! Yeah,
they got me that way too.


I would have dropped the asshole with a bench stool before he could
get away from my bench. OTOH, my bench was usually out in the open,
away from any wall, and had space to walk all the way around it so your
childish stunt would be quite obvious. I had three benches at my last
job, along with a lot of equipment cats and a 4' * 8' table for
schematics. I was working on $80,000 telemetry receivers. The only way
to pull your stunt would be to drill a hole in the bench, and try to
hide the hose.

I'll keep that in mind if I ever hire you.

100% disabled, these days.

(note to self: use hollow floor)

Concrete slab.

(note to self: stay out of stool range)

And those old die cast HP equipment cases! The handles make them
easy to hold on to while you wind up for the 8660 toss! ;-)

We had a jerk there that walked around hitting people in the back
when they were concentrating on the item they were testing or
troubleshooting. He did it to an old man working on the only high
voltage product in out line, and almost knocked him off his bench stool.
I waited till he was talking to the test department supervisor and told
him if he ever did that to me, or to Jerry again I was going to knock
him on his ass. He puffed up like a blowfish and informed both of us
that he was 100 pounds heavier than me. I pointed to one of our new,
OSHA approved 75 pound padded bench stools and told him it would
probably take the top of his head off, and to leave people alone. He
snarled at our boss and said, That SOB has a big problem. Our boss
grinned and said, It sounds like he gave you some good advice! He was
just about the only tech there who wasn't a Veteran, and had no idea
what would happen when he went too far. He was too stupid to understand
what he was doing was considered assult. He complained to another
Veteran on the test floor who informed him that old soldiers can still
kill, when they are provoked long enough. He finally realized he could
end up dead if he didn't stop.


--
http://improve-usenet.org/index.html

aioe.org, Goggle Groups, and Web TV users must request to be white
listed, or I will not see your messages.

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your account: http://www.usenettools.net/ISP.htm


There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you're crazy.

 

[Michael A. Terrell]

"Michael A. Terrell" wrote:

Tim Wescott wrote:

On Fri, 30 Jan 2009 14:03:25 -0500, Michael A. Terrell wrote:

Benj wrote:

On Jan 26, 4:35 pm, Rich Grise <r...@example.net> wrote:

When I was in USAF electronics tech school, somebody would always
send some newbie off in search of "a can of grid-leak bias". ;-)

(also 20 feet of flight line, a bucket of prop wash, and a buffer
amplifier (when you're buffing the floor).)

Heh. Yeah newbies always get it. When I was a newbie at the Chemistry
Dept. instrument repair shop, the standard thing was to "tygonize"
them. What you'd do is get a nice length of tygon tubing and a large
cigar. Then when one day when the unsuspecting newbie has some hyper-
expensive piece of gear on his bench he's fixing, you surreptitiously
snake the tubing into the instrument and when the newbie thinks he's
got it fixed and flips the power on, from around the corner you light
the cigar and blow smoke into the machine which then pours out of it
like it's on fire! Much fun then ensues as newbie panics! Yeah,
they got me that way too.


I would have dropped the asshole with a bench stool before he could
get away from my bench. OTOH, my bench was usually out in the open,
away from any wall, and had space to walk all the way around it so your
childish stunt would be quite obvious. I had three benches at my last
job, along with a lot of equipment cats and a 4' * 8' table for
schematics. I was working on $80,000 telemetry receivers. The only way
to pull your stunt would be to drill a hole in the bench, and try to
hide the hose.

I forgot to mention that at times I have severe allergies to tobacco
smoke. I had one moron light up and blow smoke in my face one day,
knowing how it affected me. He was laughing his ass off. The next
morning, he did his usual of switching on the central AC and lighting up
in front of the intake. He took one puff and ran to throw up. I had
used an entire can of Lysol just before he walked in, so when he took
his deep puff, he nearly passed out. Problem solved, and no blood was
shed that day.

I'll keep that in mind if I ever hire you.

100% disabled, these days.

(note to self: use hollow floor)

Concrete slab.

(note to self: stay out of stool range)

And those old die cast HP equipment cases! The handles make them
easy to hold on to while you wind up for the 8660 toss! ;-)



We had a jerk there that walked around hitting people in the back
when they were concentrating on the item they were testing or
troubleshooting. He did it to an old man working on the only high
voltage product in out line, and almost knocked him off his bench stool.
I waited till he was talking to the test department supervisor and told
him if he ever did that to me, or to Jerry again I was going to knock
him on his ass. He puffed up like a blowfish and informed both of us
that he was 100 pounds heavier than me. I pointed to one of our new,
OSHA approved 75 pound padded bench stools and told him it would
probably take the top of his head off, and to leave people alone. He
snarled at our boss and said, That SOB has a big problem. Our boss
grinned and said, It sounds like he gave you some good advice! He was
just about the only tech there who wasn't a Veteran, and had no idea
what would happen when he went too far. He was too stupid to understand
what he was doing was considered assult. He complained to another
Veteran on the test floor who informed him that old soldiers can still
kill, when they are provoked long enough. He finally realized he could
end up dead if he didn't stop.

--
http://improve-usenet.org/index.html

aioe.org, Goggle Groups, and Web TV users must request to be white
listed, or I will not see your messages.

If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm

There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you're crazy.

--
http://improve-usenet.org/index.html

aioe.org, Goggle Groups, and Web TV users must request to be white
listed, or I will not see your messages.

If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm


There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you're crazy.