On Mon, 06 Jun 2005 15:05:43 GMT, "Henry Kolesnik"
wrote:

Please tell me more about melting the finals and a bit more explanation of
what was happening?

Hi Hank,

Direct observation offered a glowing plasma between the filament and
the plate. It was football shaped rather than beam-like or an
amorphous cloud. One point of the football touched the cherry red
plate. Following a quick power-down, that point on the plate did not
exist anymore as there was a hole. Couldn't really tell, but no doubt
the grid suffered just as much in its own way.

I suppose plates have become more robust over the years since that
amazing demonstration. I helped fix one friend's Amp when it failed
along with his antenna (or t'other way round as the chain of causality
would suggest). His Amp simply quit working suddenly during bad
weather. Fuses checked - OK. No interlocks were open - OK. The tube
looked good at a glance - OK. HV Supply looked good - OK. The
filaments failed to light up - odd, but consistent. Time to crack
open the case. Pulled the tube and measured its filament continuity -
OK. Measured filament supply - OK. Things were really getting
strange. Time to bust the chassis open and really look. There on the
baseplate were several small pools of solder in a circular pattern -
how odd. Close scrutiny of connections revealed bright and soldered
wires to everything - OK. Time to look at the tube again. Every pin
was solder free - that was on the chassis base plate. [dirge played
here] The filaments' wires were making enough contact to measure
continuity, but no where enough to support real power.

In other tubes I've seen the heat become so extreme that the glass
envelope slumped into the vacuum and enclosed the plate structure like
taffy. This didn't even crack the glass (or it had simply re-fused).
Tube still worked afterwards though (so I would suppose the glass
never cracked). One occasion was actually due to a bias problem
created when the cathode load shorted. Lack of bias protection sent
the circuit into massive conduction. Of course the short came about
because of an initial excessive conduction (surprising in its own
right because the common failure mode is to open).

I've also seen stressed thyratrons so mismatched that they filled the
workspace with their purple glow like a floodlight. Thankfully fuses
work as I did not want to be near that final testimony.

Now, that was the short list of Bottle failures. I have another list
of melted state failures too, but their evidence is usually better
hidden and less dramatic - heat sinking generally spreads the risk,
so to speak. And speaking of heat sinks, I've drawn a number of
blisters from those that normally only warmed my hand. Note there
should be emphasis on normally warm and the obvious contradiction with
blisters.

Experience with failure has strongly correlated with heat and
mismatch. Heat was born by resistance. Resistance is part of life
and amplifiers. Heat comes in two forms. Slow-like, which is
generally current based; and sudden, which is generally voltage based.
I've felt along heatsinks immediately following failure that were as
cool/tepid as usual, or ominously cooler! The sudden heat of arc-over
in silicon can destroy just as effectively as the long slow broil of a
plate turning to slag.

Every mismatch in the Amateur experience is a probablistic spin of the
wheel of misfortune. Sometimes the wheel stops on the slow bake that
aborbs into heatsinks and you notice unusual smell, or your fan
running on too long - Quick! do something, and you survive. Other
times there's the snap of finality. Both of these examples are for
those with keen senses, and often failure comes as a whimper.

Most suffers usually discover what matching is for, even if they don't
know how it works.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
Every mismatch in the Amateur experience is a probablistic spin of the
wheel of misfortune. Sometimes the wheel stops on the slow bake that
aborbs into heatsinks ...

Current maximum, Ifor+Iref in phase. Vtot = |Vfor|-|Vref|

Other times there's the snap of finality.

Voltage maximum, Vfor+Vref in phase. Itot = |Ifor|-|Iref|
--
73, Cecil http://www.qsl.net/w5dxp


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Richard

I've seen 3-500Z where the solder had melted out of the filament pins.

I have some 811 from my 30L-1 that have holes in the plates, they still work
quite well. It's been 15 years since I recall finding the holes in the
plate sides and replacing. In additon I can't recall the reason for the
holes but it had to be either
1. overdriving (which I don't think I did, 100 watt Icom)
2. high swr which I know has been over 10 to 1, but I can't see how that
could do it..
3. Light loading

But in any event for something to melt we need dissipation and only
resistance can do that!

--

73
Hank WD5JFR
Still learning, un-learning and re-learning

On Mon, 06 Jun 2005 20:52:52 GMT, "Henry Kolesnik"
wrote:

But in any event for something to melt we need dissipation and only
resistance can do that!


Hi Hank,

Unfortunately as much as you and I agree on that bedrock principle,
others with Simpson Ohmmeter in hand would glare goggle eyed at us and
say that plate has no resistance to speak of and that no amount of
current through its Ohmic resistance could ever bring about enough
heat to produce the effects so obviously witnessed. One of the most
enraging questions I've asked
"If it is not the value I've offered, what value is it?"

Well, I've never been given a quantitative answer, however I've seen
enough carefully crafted mathematical proofs in this group to replace
substantive results so easily seen. There is some irrefutable logic
in circulation that clearly reveals that what we've experienced just
couldn't be.

Glasses will be need to be readjusted for such extreme myopic
aberrations. There are two principles involved in what is called
Plate Resistance, and the first and foremost is not even related to
the plate at all. It is called the work function of the cathode
emissivity. So, in fact it is more proper to refer to this usual loss
as Cathode Resistance, not Plate Resistance. The cathode is the
fundamental limit on power generated.

What Plate Resistance is, is the ill termed substitution for Plate
dissipation. If folks want to work their Simpson, they would blow an
aneurysm trying to measure the resistance from cathode (filaments have
the same work function issue too) to plate. In fact, the hobby horse
argument of it is not resistance at all, but some figurative charting
artifice called a "load line" usually appears in the last gasp.

Plate Dissipation is resistance clear and simple in spite of the
failure of conventional tools to measure a common physical property.
Newton would have recognized it, it is called inertia.

Once the work function is overcome (the job of the grid), then Plate
voltage dominates through the acceleration of charge beyond the grid,
toward the plate. That stream of electrons (and there is no doubt
about actual current flow in easily counted, significant populations
of electrons) is elevated to 90% the speed of light. This current
flow is entirely different from what current flows in the remainder of
the Plate load. That is also known as displacement current and
electrons are shuffling along at a placid meter per second rate.
Plate current and displacement current are equal in amplitude and
phase, but not in motion nor kinetics.

NOW. When that same stream encounters the Plate - WHAM! If anyone
here has walked into the wall, and NOT encountered resistance, then we
will call you Casper.

Inertia reveals that to slow a mass in a distance results in
acceleration (negative in this instance) and that property is called
Force. Force over time expends calories and is expressed in any
number of systems and units - Watts is one, Degrees is another. We
could abstract to Horsepower and Candelas (the plate glows too).

We know the speed, not many here would give it much though, but none
would know the length interval of going at that speed to going zero
(0). It is roughly two atoms distance into the metal of the plate. I
will leave those calculations of Force to the student to compute or I
can provide it from notes of correspondence with Walt Maxwell and
Richard Harrison from a round robin discussion several years ago.

Hank, does this fulfill your earlier question as to "what" is
happening? I first gave you many examples, I hope this segue into
real physics fills in their actuality. Too many correspondents demand
that I open the source and point at a 50 Ohm carbon composition
resistor that is the "source resistance."

73's
Richard Clark, KB7QHC

Richard
Thanks for your explanation, I'm still thinking it over since its been 40
years since I've studied any tube theory. .. I recall many years ago
watching a guy trying to fix an old radio. IIRC it had an 80 rectifier and
right after the radio was turned on and started to warm up a blue cloud
could be seen in the tube as the plates started to turn redder and redder.
He would turn it off, change a part and check it again. I don't think he
fixed it before the 80 went south. Later I figured out that he probably
had a shorted filter cap.
In this case the diode's plate dissipation rating was exceeded and it
melted. The electrons slamming into the plate have a lot of kinetic energy
to transfer. and heat up the plate. This results in lower efficiency as
this power isn't delivered to the load. Now the diodes resistance can be
easily calculated but I'm not sure how to visualize it. Is this where your
term cathode resistance enters the picture?
tnx

--

73
Hank WD5JFR
"Richard Clark" wrote in message
...
On Mon, 06 Jun 2005 20:52:52 GMT, "Henry Kolesnik"
wrote:

But in any event for something to melt we need dissipation and only
resistance can do that!


Hi Hank,

Unfortunately as much as you and I agree on that bedrock principle,
others with Simpson Ohmmeter in hand would glare goggle eyed at us and
say that plate has no resistance to speak of and that no amount of
current through its Ohmic resistance could ever bring about enough
heat to produce the effects so obviously witnessed. One of the most
enraging questions I've asked
"If it is not the value I've offered, what value is it?"

Well, I've never been given a quantitative answer, however I've seen
enough carefully crafted mathematical proofs in this group to replace
substantive results so easily seen. There is some irrefutable logic
in circulation that clearly reveals that what we've experienced just
couldn't be.

Glasses will be need to be readjusted for such extreme myopic
aberrations. There are two principles involved in what is called
Plate Resistance, and the first and foremost is not even related to
the plate at all. It is called the work function of the cathode
emissivity. So, in fact it is more proper to refer to this usual loss
as Cathode Resistance, not Plate Resistance. The cathode is the
fundamental limit on power generated.

What Plate Resistance is, is the ill termed substitution for Plate
dissipation. If folks want to work their Simpson, they would blow an
aneurysm trying to measure the resistance from cathode (filaments have
the same work function issue too) to plate. In fact, the hobby horse
argument of it is not resistance at all, but some figurative charting
artifice called a "load line" usually appears in the last gasp.

Plate Dissipation is resistance clear and simple in spite of the
failure of conventional tools to measure a common physical property.
Newton would have recognized it, it is called inertia.

Once the work function is overcome (the job of the grid), then Plate
voltage dominates through the acceleration of charge beyond the grid,
toward the plate. That stream of electrons (and there is no doubt
about actual current flow in easily counted, significant populations
of electrons) is elevated to 90% the speed of light. This current
flow is entirely different from what current flows in the remainder of
the Plate load. That is also known as displacement current and
electrons are shuffling along at a placid meter per second rate.
Plate current and displacement current are equal in amplitude and
phase, but not in motion nor kinetics.

NOW. When that same stream encounters the Plate - WHAM! If anyone
here has walked into the wall, and NOT encountered resistance, then we
will call you Casper.

Inertia reveals that to slow a mass in a distance results in
acceleration (negative in this instance) and that property is called
Force. Force over time expends calories and is expressed in any
number of systems and units - Watts is one, Degrees is another. We
could abstract to Horsepower and Candelas (the plate glows too).

We know the speed, not many here would give it much though, but none
would know the length interval of going at that speed to going zero
(0). It is roughly two atoms distance into the metal of the plate. I
will leave those calculations of Force to the student to compute or I
can provide it from notes of correspondence with Walt Maxwell and
Richard Harrison from a round robin discussion several years ago.

Hank, does this fulfill your earlier question as to "what" is
happening? I first gave you many examples, I hope this segue into
real physics fills in their actuality. Too many correspondents demand
that I open the source and point at a 50 Ohm carbon composition
resistor that is the "source resistance."

73's
Richard Clark, KB7QHC

On Tue, 07 Jun 2005 15:01:26 GMT, "Henry Kolesnik"
wrote:

Now the diodes resistance can be
easily calculated but I'm not sure how to visualize it. Is this where your
term cathode resistance enters the picture?

Hi Hank,

Getting electrons to "boil" off the cathode (or filament, same thing)
is not a simple task otherwise there would be no filaments needed.
Even with filaments, Edison current is not very considerable unless
you add a monomolecular layer of metal to the surface of either the
filament, or the cathode.

You may note that some tubes are described as having "Thoriated"
filaments. This is that monomolecular addition. Its purpose is to
lower the W, the work function of the interface.

It is far from odd how physics demonstrates at every stage and in
every discipline that interfaces where there is mismatch, there is
difficulty in transfering power. When an electron from the interior
of the metal crystal approaches the surface, it is repelled by that
interface due to the potential of the work function, and is attracted
by the bulk material behind it. The Thoriated surface offers a
matching mechanism between the bulk metal and the free space beyond
the surface. In classic Optics this is known as Index Matching.

To give examples as to how well a monomolecular addition performs:

A Tungsten filament (no treatment) offers a current density of ½A/cM²
This makes for a baseline.

A Thoriated Tungsten filament offers a current density of 4A/cM²

Then we step back to a cylindrical cathode employing Barium.
Such a cathode offers a current density of ½A/cM²

That seems rather regressive to use a cathode, but temperatures are
telling. The simple Tungsten filament is operating at 2500° K and the
cathode needs only to simmer along at 1000° K. This gives
considerably longer life and more efficiency (most of the power for
heating is lost through radiation). Needless to say, cathodes find
more application in low power circuits, or their surfaces are treated
with other low work function metals for greater emission.

Now, when you add a potential gradient, you also lower the work
function of the surface (but it is always an advantage to have it
lowered going into this game). This is called the Schottky effect.
One might be tempted to simply ask, why don't we up the voltage and
discard the filament? This device would be called a Cold Cathode but
the potential gradient then rises to the level where you run the risk
of secondary emission.

When that electron stream strikes the plate and raises the
temperature, it is just short enough power to present this secondary
emission. But if we were to run at 17KV or so, then the electron
stream would be so aggressive as to produce high energy effects such
as X-Ray emission.

So, to return to the resistance of this all, we have physical
impositions of cathode surface area (probably offering the prospect of
being greater than filament surface area), current density, and
potential difference. Discarding all the extraneous surface units
(cM²) and employing the proper division (E/I) we have a resistor that
glows in the dark under extremes of operation. How this fails to be
source resistance is strictly handwaving and the schematic symbolic
mysticism of demanding a carbon composition resistor.

73's
Richard Clark, KB7QHC

On Tue, 07 Jun 2005 11:44:29 -0700, Richard Clark
wrote:

When that electron stream strikes the plate and raises the
temperature, it is just short enough power to present this secondary
emission. But if we were to run at 17KV or so, then the electron
stream would be so aggressive as to produce high energy effects such
as X-Ray emission.

Something felt wrong here. I should have said:
...just short enough energy to present this secondary emission.

Richard,

This has been an entertaining monologue on electron tubes. (Must be
International Fractured Physics Week on RRAA.)

I won't attempt to address the numerous howlers, since Henry seemed
satisfied with your tale, but you might want to rethink the item you
"correct" in this message.

Secondary electron emission also occurs at much lower incident electron
energies. As a metrologist you are most likely familiar with electron
microscopy. Secondary electron emission is the typical mode of detector
operation. The incident electron energy in modern SEM's is now in the
range of 500 to 700 volts.

One of the reasons for adding more grids in vacuum tubes is to manage
secondary emission from the plate. This occurs at much less than 17 kV.

73,
Gene
W4SZ



Richard Clark wrote:
On Tue, 07 Jun 2005 11:44:29 -0700, Richard Clark
wrote:


When that electron stream strikes the plate and raises the
temperature, it is just short enough power to present this secondary
emission. But if we were to run at 17KV or so, then the electron
stream would be so aggressive as to produce high energy effects such
as X-Ray emission.


Something felt wrong here. I should have said:
...just short enough energy to present this secondary emission.