Dudes, try going to http://www.fust-electronica.nl/5881.htm

Patrick Turner.

in article , Patrick Turner at
wrote on 9/15/05 7:21 AM:

Dudes, try going to http://www.fust-electronica.nl/5881.htm

Patrick Turner.



Thanks, Patrick. Good stuff!

flipper wrote:

On Thu, 15 Sep 2005 11:21:38 GMT, Patrick Turner
wrote:

Dudes, try going to http://www.fust-electronica.nl/5881.htm

Patrick Turner.

Good read.

The article tell ppl about a number of problems one can get with tubes,
not just
5881 etc.
Gold plated grid wires and special screen coatings and fancy anode
materials improve tubes a lot.
The countries that make tubes without all these techniques cannot claim
to be making premium grade tubes.

Patrick Turner.

flipper wrote:

On Thu, 15 Sep 2005 16:54:29 GMT, Patrick Turner
wrote:



flipper wrote:

On Thu, 15 Sep 2005 11:21:38 GMT, Patrick Turner
wrote:

Dudes, try going to http://www.fust-electronica.nl/5881.htm

Patrick Turner.

Good read.

The article tell ppl about a number of problems one can get with tubes,
not just
5881 etc.

You betcha and that's what I meant.

I wish he'd gone a bit more into the actual mechanism behind 'sleeping
sickness' though.

Never put tubes to bed in a dark room.
That way they won't fall asleep :-)

Patrick Turner.



Gold plated grid wires and special screen coatings and fancy anode
materials improve tubes a lot.
The countries that make tubes without all these techniques cannot claim
to be making premium grade tubes.

Patrick Turner.

"flipper" wrote in message
...
: On Fri, 16 Sep 2005 06:41:54 GMT, Patrick Turner
: wrote:
:
: LOL. Ok, I'll remember that and leave the filaments glowing
:
: Oh wait, that's what causes it to begin with.
:
: I found it interesting because it seems to be a bit contradictory to
: the cathode stripping crowd.

Well, to put things in perspective, c.s. is not some imaginary
boutique-speak, but rather a well researched phenomenon.
Not by some internet wannabe skeptic (as in the article you
mentioned elsewhere ~reasoning~ from rectifier tubes) but
by physicists holding phd's with scientific and commercial
interest in the matter - the research & development guys
that were responsible for the production of millions of tubes
now some half a century ago.

Whether or not one should worry about it, is another matter.
I think Fabio has given the common sense approach, when using
expensive tubes , better safe than sorry :-)
In general, avoiding overstressing electrical or mechanical
components is always good practice.

BTW, the 5881 article gives one reason why a tube with grid(s)
gives a lot more potential problems with 'cathode dust' than a
rectifier - you don't want a grid as an emission source !

Rudy

"flipper" wrote in message
...
: On Sat, 17 Sep 2005 23:31:23 +0200, "Ruud Broens"
: wrote:
:
:
: "flipper" wrote in message
: .. .
: : On Fri, 16 Sep 2005 06:41:54 GMT, Patrick Turner
: : wrote:
: :
: : LOL. Ok, I'll remember that and leave the filaments glowing
: :
: : Oh wait, that's what causes it to begin with.
: :
: : I found it interesting because it seems to be a bit contradictory to
: : the cathode stripping crowd.
:
: Well, to put things in perspective, c.s. is not some imaginary
: boutique-speak, but rather a well researched phenomenon.
: Not by some internet wannabe skeptic (as in the article you
: mentioned elsewhere ~reasoning~ from rectifier tubes) but
: by physicists holding phd's with scientific and commercial
: interest in the matter - the research & development guys
: that were responsible for the production of millions of tubes
: now some half a century ago.
:
: I think you mischaracterized the person's reasoning but I'd love to
: see something by the experts you mention if you'd point me to one.

Heh, ok, googling "sputtering" with this NG will get you some earlier
info i posted; here a snippet from a Philips Tech. Library book, 1964:

"The main causes of deterioration of the cathode are evaporation and
sputtering. A well-designed coated cathode will give very slight
evaporation and sputtering, as long as the current remains below
the saturation current. If the tube is operated under suitable conditions,
both these causes of deterioration can be neglected."
- sputtering being the term for cathode stripping as used in the industry.
So far, so good. But of course, what are the less-than-suitable conditions ?

A graph shows the saturation current density for a BaO/SrO coating
as a function of the true temperature in K of the cathode (and those for
tungsten/thoriated tungsten type tubes). Over a million A/m^2 at 1300 K
or above should not be exeeded or sputtering will take place - not exactly
a problem :-)
At 500 K, however, this has fallen dramatically: a 100 mA per square meter
of cathode will get you into trouble !
For a few seconds during heating up from room temperature, if B+ is
present, the cathode will be exposed to current exeeding the saturation current.
Once above say 800K, no worries, you'll never get anywhere near problematic
current - well, maybe with power tubes operated well above their 'guidelines' :-)

Cheers,
Rudy

:
: Whether or not one should worry about it, is another matter.
: I think Fabio has given the common sense approach, when using
: expensive tubes , better safe than sorry :-)
: In general, avoiding overstressing electrical or mechanical
: components is always good practice.
:
: BTW, the 5881 article gives one reason why a tube with grid(s)
: gives a lot more potential problems with 'cathode dust' than a
: rectifier - you don't want a grid as an emission source !
:
: Rudy
:
:

A graph shows the saturation current density for a BaO/SrO coating
as a function of the true temperature in K of the cathode (and those for
tungsten/thoriated tungsten type tubes). Over a million A/m^2 at 1300 K
or above should not be exeeded or sputtering will take place - not exactly
a problem :-)
At 500 K, however, this has fallen dramatically: a 100 mA per square meter
of cathode will get you into trouble !
For a few seconds during heating up from room temperature, if B+ is
present, the cathode will be exposed to current exeeding the saturation current.

At what B+ voltage does this happen? Surely the value of B+ must be a
factor.

Once above say 800K, no worries, you'll never get anywhere near problematic
current - well, maybe with power tubes operated well above their 'guidelines' :-)

The question of cathode stripping was raised in AGA a while ago. The
OP's question was whether this is a problem for tubes operated at a few
hundred volts in audio circuits. He surmized that this issue was
mainly of concern in high voltage transmitters. The OP said he ignored
the standby SW in his guitar amp and did not notice premature tube
wear.

Best regards,
Joe

"Joseph Meditz" said:

The question of cathode stripping was raised in AGA a while ago. The
OP's question was whether this is a problem for tubes operated at a few
hundred volts in audio circuits. He surmized that this issue was
mainly of concern in high voltage transmitters. The OP said he ignored
the standby SW in his guitar amp and did not notice premature tube
wear.


That's probably because in most guitar amps, the power tubes are
abused so hard that their useful life is short enough not to encounter
any problems due to cathode stripping or even cathode poisoning.

OTOH, how do we know that an exhausted set of tubes *didn't* suffer
from beforementioned problems? :-)

--

"Audio as a serious hobby is going down the tubes."
- Howard Ferstler, 25/4/2005

"Sander deWaal" wrote in message
...
: "Joseph Meditz" said:
:
: The question of cathode stripping was raised in AGA a while ago. The
: OP's question was whether this is a problem for tubes operated at a few
: hundred volts in audio circuits. He surmized that this issue was
: mainly of concern in high voltage transmitters. The OP said he ignored
: the standby SW in his guitar amp and did not notice premature tube
: wear.
:
:
: That's probably because in most guitar amps, the power tubes are
: abused so hard that their useful life is short enough not to encounter
: any problems due to cathode stripping or even cathode poisoning.
:
: OTOH, how do we know that an exhausted set of tubes *didn't* suffer
: from beforementioned problems? :-)
:
: --
:
: "Audio as a serious hobby is going down the tubes."
: - Howard Ferstler, 25/4/2005

Darn, that's exactly what i was going to post, you beat me to it,
again :-), Sander.

How much the usefull lifetime of a tube is reduced by the start-up
strippin ? No data on that, Joseph, or at least i've not come across that.
My guestimate: anywhere between 0 and 15 %. No biggie unless it
happens to be a rare tube. And an increase in the change of catastrophic
failure, in case the material lost from the cathode finds it way to the
worst places - Murphy's law makes that something to think about :-)
Some of my conclusions:
- an SS rectifier & slow turn-on filament heating is the worst combination,
aggravating the effect by prolonging the low-temp cathode phase
- the effect must be a lot more significant for power tubes than for
pre-amp / driver tubes
- an alternative to delayed B+ circuitry may be to use filament heating
during start-up in a way to minimize the relatively cold cathode phase

Rudy
btw Sander, heb je al zo'n i Love 180 km/u sticker ? ;-)

Ruud Broens wrote:

"Sander deWaal" wrote in message
...
: "Joseph Meditz" said:
:
: The question of cathode stripping was raised in AGA a while ago. The
: OP's question was whether this is a problem for tubes operated at a few
: hundred volts in audio circuits. He surmized that this issue was
: mainly of concern in high voltage transmitters. The OP said he ignored
: the standby SW in his guitar amp and did not notice premature tube
: wear.
:
:
: That's probably because in most guitar amps, the power tubes are
: abused so hard that their useful life is short enough not to encounter
: any problems due to cathode stripping or even cathode poisoning.
:
: OTOH, how do we know that an exhausted set of tubes *didn't* suffer
: from beforementioned problems? :-)
:
: --
:
: "Audio as a serious hobby is going down the tubes."
: - Howard Ferstler, 25/4/2005

Darn, that's exactly what i was going to post, you beat me to it,
again :-), Sander.

How much the usefull lifetime of a tube is reduced by the start-up
strippin ? No data on that, Joseph, or at least i've not come across that.
My guestimate: anywhere between 0 and 15 %. No biggie unless it
happens to be a rare tube. And an increase in the change of catastrophic
failure, in case the material lost from the cathode finds it way to the
worst places - Murphy's law makes that something to think about :-)
Some of my conclusions:
- an SS rectifier & slow turn-on filament heating is the worst combination,
aggravating the effect by prolonging the low-temp cathode phase
- the effect must be a lot more significant for power tubes than for
pre-amp / driver tubes
- an alternative to delayed B+ circuitry may be to use filament heating
during start-up in a way to minimize the relatively cold cathode phase

Rudy

I was asking myself if some of those european tubes, like PCL805, have
the bright heater glow on startup to avoid cathode stripping?
Is anybody wise to this?

Kind regards, Eike
--

"Ruud Broens" said:

btw Sander, heb je al zo'n i Love 180 km/u sticker ? ;-)


Neuh, ik plak geen stikkers, ik *rijd* gewoon 180 :-))))

--

"Audio as a serious hobby is going down the tubes."
- Howard Ferstler, 25/4/2005

"Sander deWaal" wrote in message
...
: "Ruud Broens" said:
:
: btw Sander, heb je al zo'n i Love 180 km/u sticker ? ;-)
:
:
: Neuh, ik plak geen stikkers, ik *rijd* gewoon 180 :-))))
:
Well, you know what they say:
a man of action needs good traction :-)
R.

"Eike Lantzsch, ZP6CGE" said:

I was asking myself if some of those european tubes, like PCL805, have
the bright heater glow on startup to avoid cathode stripping?
Is anybody wise to this?


What I know is that most Philips tubes and their brand derivates
(Valvo, Mazda etc) have a black heater coating, where the heater goes
inside the cathode. This coating is to prevent heater-cathode shorts.
The lowest (white) part of the heater isn't coated and will therefore
light up brightly when heater voltage is applied.

Telefunkens, Siemens etc. don't suffer from this effect..

--

"Audio as a serious hobby is going down the tubes."
- Howard Ferstler, 25/4/2005

"Eike Lantzsch, ZP6CGE" wrote:

Ruud Broens wrote:

"Sander deWaal" wrote in message
...
: "Joseph Meditz" said:
:
: The question of cathode stripping was raised in AGA a while ago. The
: OP's question was whether this is a problem for tubes operated at a few
: hundred volts in audio circuits. He surmized that this issue was
: mainly of concern in high voltage transmitters. The OP said he ignored
: the standby SW in his guitar amp and did not notice premature tube
: wear.
:
:
: That's probably because in most guitar amps, the power tubes are
: abused so hard that their useful life is short enough not to encounter
: any problems due to cathode stripping or even cathode poisoning.
:
: OTOH, how do we know that an exhausted set of tubes *didn't* suffer
: from beforementioned problems? :-)
:
: --
:
: "Audio as a serious hobby is going down the tubes."
: - Howard Ferstler, 25/4/2005

Darn, that's exactly what i was going to post, you beat me to it,
again :-), Sander.

How much the usefull lifetime of a tube is reduced by the start-up
strippin ? No data on that, Joseph, or at least i've not come across that.
My guestimate: anywhere between 0 and 15 %. No biggie unless it
happens to be a rare tube. And an increase in the change of catastrophic
failure, in case the material lost from the cathode finds it way to the
worst places - Murphy's law makes that something to think about :-)
Some of my conclusions:
- an SS rectifier & slow turn-on filament heating is the worst combination,
aggravating the effect by prolonging the low-temp cathode phase
- the effect must be a lot more significant for power tubes than for
pre-amp / driver tubes
- an alternative to delayed B+ circuitry may be to use filament heating
during start-up in a way to minimize the relatively cold cathode phase

Rudy

I was asking myself if some of those european tubes, like PCL805, have
the bright heater glow on startup to avoid cathode stripping?
Is anybody wise to this?

Quite a few IDH twin triodes glow bright for a second at turn on.
These tubes have a piece of special metal which turns bright like a light bulb
at turn on with a large increase in resistance until the rest of the heater
element
rises in temperature slowly which increases its resistance so the bright
element goes dull and lowers its R and the tube incrush current is thus better
limited
at turn on.
This was important where many tubes were used, in a large mixing desk,
or multiple amp system, or wherever lots of tubes were used.

Patrick Turner.



Kind regards, Eike
--

Ruud Broens wrote:


How much the usefull lifetime of a tube is reduced by the start-up
strippin ? No data on that, Joseph, or at least i've not come across that.
My guestimate: anywhere between 0 and 15 %. No biggie unless it
happens to be a rare tube. And an increase in the change of catastrophic
failure, in case the material lost from the cathode finds it way to the
worst places - Murphy's law makes that something to think about :-)

It ought to be blindingly obvious that it is not related to tube
hours but to _how many times the tube is turned on from cold_. So
in guitar amps which usually don't run for more than a few hours
at a time this is possibly a greater problem than in a hi-fi
application where longer runs are much commoner.

The real measure would be how many 'start from cold' cycles the
tube can endure before failure. A useful secondary measure would
be how many hours a tube can run before it would have been better
to switch off and restart. I.e how many hours a start-up cycle is
worth.


best

Andy

"flipper" wrote in message
...
: On Sun, 18 Sep 2005 17:56:22 +0200, "Ruud Broens"
: wrote:
: At 500 K, however, this has fallen dramatically: a 100 mA per square meter
: of cathode will get you into trouble !
: For a few seconds during heating up from room temperature, if B+ is
: present, the cathode will be exposed to current exeeding the saturation
current.
: Once above say 800K, no worries, you'll never get anywhere near problematic
: current - well, maybe with power tubes operated well above their 'guidelines'
:-)
:
: For what tubes and what voltages? I mean, it's obvious there must be
: SOME voltage and that raises the question of whether it's a linear
: function, or not, and whether there's a minimum, or not. etc.
:
: That was the point of the person you like calling "some Internet
: wannabe skeptic." He didn't dispute cathode stripping. He claimed
: there was a minimum threshold below which it wasn't a serious issue.

err, no, naming it "so-called" implies it is just some imaginary effect.
And reasoning that it doesn't seem to be there with rectifier tubes,
_hence_ not an effect with any tube is just nonsense. Tubes are designed
with a specific application in mind, just like SS, so a manufacturer that
knows the mechanism causing sputtering can take measures in design
& manufacturing. Let's say you were a startup tube manufacturer, just
gained knowledge about the described mechanism, what would you do ?

Rudy

Patrick Turner wrote:


"Eike Lantzsch, ZP6CGE" wrote:

I was asking myself if some of those european tubes, like PCL805, have
the bright heater glow on startup to avoid cathode stripping?
Is anybody wise to this?

Quite a few IDH twin triodes glow bright for a second at turn on.
These tubes have a piece of special metal which turns bright like a light bulb
at turn on with a large increase in resistance until the rest of the heater
element
rises in temperature slowly which increases its resistance so the bright
element goes dull and lowers its R and the tube incrush current is thus better
limited
at turn on.
This was important where many tubes were used, in a large mixing desk,
or multiple amp system, or wherever lots of tubes were used.

Patrick Turner.

Uha! Thanx for the explanation :-) So it is not really the filament
that's glowing bright for a moment.

Kind regards, Eike
--
Lions go to absurd lengths to retain the posession of their skins.
- Stewart Edward White 1913

"flipper" wrote in message
...
: On Tue, 20 Sep 2005 20:55:35 +0200, "Ruud Broens"
: wrote:
:
:
: "flipper" wrote in message
: .. .
: : On Sun, 18 Sep 2005 17:56:22 +0200, "Ruud Broens"
: : wrote:
: : At 500 K, however, this has fallen dramatically: a 100 mA per square meter
: : of cathode will get you into trouble !
: : For a few seconds during heating up from room temperature, if B+ is
: : present, the cathode will be exposed to current exeeding the saturation
: current.
: : Once above say 800K, no worries, you'll never get anywhere near problematic
: : current - well, maybe with power tubes operated well above their
'guidelines'
: :-)
: :
: : For what tubes and what voltages? I mean, it's obvious there must be
: : SOME voltage and that raises the question of whether it's a linear
: : function, or not, and whether there's a minimum, or not. etc.
: :
: : That was the point of the person you like calling "some Internet
: : wannabe skeptic." He didn't dispute cathode stripping. He claimed
: : there was a minimum threshold below which it wasn't a serious issue.
:
: err, no, naming it "so-called" implies it is just some imaginary effect.
:
: Except your interpretation of 'it' is incorrect. He's saying 'it' is
: an imaginary effect at the low voltages typically used in "small
: receiving or transmitting tubes".

...and it should be obvious from my posting that this is not the case
are you arguing for argument's sake ?
(i leave it up to you to find a mental model that shows that a high
voltage will lead to a somewhat longer 'strippin danger zone'
:
: He clearly says cathode stripping "occurs at high voltage, typically
: above 10 kilovolts" so 'it' is not imaginary.

...and it should be obvious from my posting that this is not the case

:
: Maybe his memory is incorrect and it's 1kV, and maybe he's wrong
: entirely. I don't know but one should argue against the substance of
: what he said, not a contrived interpretation of it.
:
: And reasoning that it doesn't seem to be there with rectifier tubes,
: _hence_ not an effect with any tube is just nonsense.
:
: He used that as an example, not the basis of his reasoning.
: -) play it again, Sam.

: It clearly doesn't apply if the argument is cathode dust depositing on
: a grid but it might apply if the argument is cathode emission decay
: from material depletion.
:
: Tubes are designed
: with a specific application in mind, just like SS, so a manufacturer that
: knows the mechanism causing sputtering can take measures in design
: & manufacturing.
:
: I don't see how that answers any of the questions and someone
: unfamiliar with the delayed B+ discussion might think you're
: suggesting the manufacturer has taken care of it with "measures in
: design& manufacturing" so don't worry about it.
:
...in the case of a _rectifier tube_

: Let's say you were a startup tube manufacturer, just
: gained knowledge about the described mechanism, what would you do ?
:
: Since I'm unfamiliar with the intricacies of tube manufacture I can't
: answer that question but one obvious thought would be to use a
: material that doesn't strip under the expected operating conditions,
: if such a material existed.
:
yep, a distinct possiblity is to use a different formulation, not necessarily
having the best efficiency, that is the lowest work function giving highest
electron emission per Watt of heating power. Another to use a large
cathode area. Use a substrate of a nickel alloy that is a better heat
conductor therefore minimizing area's of lower than average temperature,
overdimensioning the heater filament, etc. etc. This is what engineering is
about,
eh ?
Rudy

"flipper" wrote in message
...
: On Wed, 21 Sep 2005 15:36:58 +0200, "Ruud Broens"
: wrote:
: : : At 500 K, however, this has fallen dramatically: a 100 mA per square
meter
: : : of cathode will get you into trouble !
: : : For a few seconds during heating up from room temperature, if B+ is
: : : present, the cathode will be exposed to current exeeding the saturation
: : current.
:
: I didn't see anything that dealt with how much voltage was needed to
: cause stripping.
:
: are you arguing for argument's sake ?
:
: Only what you make an argument that isn't valid.
:
: (i leave it up to you to find a mental model that shows that a high
: voltage will lead to a somewhat longer 'strippin danger zone'
:
: That wouldn't be the model needed. The notion that voltage matters
: would use a model similar to minimum work function and there being
: some threshold below which there isn't enough to cause the process to
: take place.
:
: Why is it obvious when you said nothing about voltage?
:
: : Tubes are designed
: : with a specific application in mind, just like SS, so a manufacturer that
: : knows the mechanism causing sputtering can take measures in design
: : & manufacturing.
: :
: : I don't see how that answers any of the questions and someone
: : unfamiliar with the delayed B+ discussion might think you're
: : suggesting the manufacturer has taken care of it with "measures in
: : design& manufacturing" so don't worry about it.
: :
: ..in the case of a _rectifier tube_
:
: Well, how in the world am I supposed to know you're talking about
: rectifier tubes when all you say is "Tubes are designed..."
:
: : Let's say you were a startup tube manufacturer, just
: : gained knowledge about the described mechanism, what would you do ?
: : This is what engineering is about, eh ?
:
: Sure is. And you're convincing me cathode stripping shouldn't be a
: problem.

Sigh. Some clippin to cut the repetitive postin'
OK, i should have stated it is obvious to someone who
gives the matter some thought - my mistake.
Sputtering is a *current issue*, clear ?
Emission is a function of the momentary cathode temperature (& efficiency
as in _having a low work function_), actual current is determined by the circuit
Vak & bias , clear ??
At room temperature, all Ia-Vak curves are flatlined on the x-axis, clear ???
There is then _no current_, whatever the supply voltage may happen to be.
Hence there is _no stripping_ (at very high voltages, a secondary effect may
take place, that is electrostatic forces 'pulling' chips of the cathode coating,
but *that* would be something completely ignorable at normal circuit voltages)

Now we start to ramp up the cathode temperature. Hey, presto, the flatliners
come alive, that is, the tube's curves rotate anti-clockwise from the x-axis
toward
the position they will have at nominal heating.
Engaging grey matter..
High Vak combined with a cathode biasing scheme is the worst case with regards
to sputtering at this stage. Why ? Suppose we have a power tube with an ample
100 cm^2 cathode area (actually much smaller, but easy calculating for ya).
At 500K, a cathode current over 1mA will exceed the saturation current in this
case.
(Below 500K the emission is so low, that the circuit configuration does not
matter,
as the emission capacity itself becomes the current limiting factor)
He, isn't it so that transfer curves are running bottom left-top right wise ?
That holds, no matter what the cathode temperature (above 500K & below
filament destruction limits, obviously, so the higher the Vak, the sooner the
circuit determined current will top that 1 mA during heating up from 500K
upwards. Clear now ????

I suppose with this headstart you can work out what i said about a power tube
with cathode bias in this case.

High voltage tubes usually are tungsten or thoriated tungsten type DH tubes.
This is definitely low efficiency, but it increases reliability. Why?
The effect of cathode-poisoning becomes a severe problem at high voltages
as ionized molecules are hitting the cathode real hard (acceleration - voltage)
That brings down emission real fast, rendering the tube useless.
thT can stand more of this bombardement than a cathode coating of BaO/SrO,
Tungsten even better, but at the expense of an even worse efficiency.
Engineering again, eh ?
cheers,
Rudy