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Author Topic: • Favorite Old Wives' Tales •  (Read 31529 times)
WS3N
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« Reply #135 on: November 18, 2011, 07:49:09 AM »

I'm a simple soul, and all this talk of photons etc makes my head spin Smiley

So, I looked at a simple modelling experiment. I modelled a 20m, centre-fed, Inverted-V, half-wave dipole with its apex at 35ft and the two ends at 25ft. I noted:
Maximum radiation at 31 degrees elevation; Radiation at 10 degrees elevation +0.87dBi

Then I flipped the dipole - apex now at 25ft and the ends at 35ft. I then noted:
Maximum radiation at 34 degrees elevation; Radiation at 10 degrees elevation -0.08dBi

So, flipping the dipole raised the angle of maximum radiation, and reduced the radiation at 10 degrees elevation - an effect equivalent to a drop in mean height.

What could explain that other than that the centre of the dipole, where the current is highest, makes more contribution to the Far-Field radiation than do the ends?

Steve G3TXQ

Although, as Tom has pointed out several times, these MoM programs calculate the radiation from the currents in the segments. They do not include the "new" physics, so the results they produce should be no more satisfying to some than anything else offered in this thread. The fact that their results agree with experiment will be of no consequence.
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N0YXB
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« Reply #136 on: November 18, 2011, 07:59:04 AM »




So here is the real point, is it worth the time to point this all out? Or does everyone realize it all? Are the bad theories doing damage, or are they no concern? In my experience, gross mistakes in theory seriously hurt amateur radio. There are baluns popularly accepted as baluns that don't work, and actually force unbalance. There are baluns on the input of tuners. There are amplifier tubes ruined by modifications like reducing filament voltage outside, or near the lower limit, of allowable voltage.  

73 Tom
[/quote]

I agree, this stuff does inflict damage in the long run.  I believe we've all known someone who had alternate theories about Electronics and Physics.  It's an interesting personality type in that they believe that they have found flaws in scientific theories and the rest of us are just not smart enough to understand, so we stick with the dogma that Newton, Maxwell, Einstein, etc have left us. 

Of course this personality type can never provide proof for their theories.  So when faced with rational arguments, they don't participate and then begin spewing personal attacks or just ignore evidence that's contrary to their theories.  It's as if some of their scientific knowledge came from Star Trek.

This thread and the cosmic ray thread have been interesting from the perspective of watching how the ego clings to nonsense.  But in the long run, it's not good for amateur radio.

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AG6K
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« Reply #137 on: November 18, 2011, 08:04:50 AM »

Never trust an author who cannot provide a reference except himself and what he says others say.

  Eimac states that each 3% increase in filament potential above that which produces full PEP decreases the emissive life of the tungsten dicarbide layer by 50%.  If one puts this relationship into a math formula, one arrives at (V2/V1)23.4. . . Checking the formula:  ((1.0/1.03)23.4= 0.500 . Real world example:  A stock TL-922 being operated from 240VAC mains:  The filament V at the sockets is 5.31v.  The max/min filament V rating is 5.25v/4.75v.  If the filament V is reduced from 5.31v to 4.8v, the emissive life is (5.31v/4.8v)23.4 = 10.6 x what it would have been at 5.31v.
  This formula was included in the  article "The Nearly Perfect Amplifier" which was published in the January, 1994 issue of QST Magazine.
cheers Scott
Rich, ag6k

 Tom R.:  After digging through my notes this morning I discovered that there were three sources to the bit about increasing emissive life of a directly-heated cathode -- a.k.a. Th-W filament -- by  reducing filament V.  The sources:
1.    Eimac's Technical Data for the 8959** tetrode,  p.4, under Filament Operation it says:  " At rated filament voltage the peak emission is many times the amount need for communications service.  Reducing the filament voltage reduces the filament temperature.  A small decrease in filament temperature substantially increases filament life.".  .  Eimac goes on to describe how to correctly reduce filament V. : "Gradually reduce filament voltage until there is a noticeable reduction in plate current or power output, or an increase in distortion.  Then increase the filament voltage several tenths of a volt above the point where performance degradation occurred."  Since the 8959 has a 15.5v filament, 0.3v is a 2% increase. 
2.  A Ham friend in San Diego who maintains a FM broadcast transmitter that uses 1, 4CX15,000A told me that he gets c. 22,000 hours (2.5 years) of operation out of Econco rebuilt tubes by operating the filament  2% above the performance degradation point throughout their life.  He said he does this because Econco recommended it. 
3.  When I inquired about properly operating the filament of my Econco rebuilt 8170 with Bill Barkley at Econco Broadcast Services he told me to operate the filament at 2% above the PEP degradation point because every 3% increase in filament potential reduces the life of the tungsten dicarbide layer by half -- and it this layer that does over 99.5% of the electron emitting.  If this is true then Eimac was definitely right about the "substantial increase in filament life." .   Barkley went on to describe how they rebuild the  ditungsten carbide layer by filling the envelope with acetylene (C2H2) gas and running the filament.  The C atoms in the acetylene molecule combines with hot W atoms to form ditungsten carbide, (W2C) and the remaining H2 is pumped out of the envelope. 
**  note - the 8959 is a 500 watt dissipation* tetrode -- *control grid.
Sorry about the flub Tom.
cheers
•••  Rich, ag6k


So as we all see....

when pressed for Eimac's data, Rich quotes himself as the Eimac example.

It is so easy to do things right and reference sources, but Rich cannot reference anyone but himself for most of what he claims.

Eimac, unfortunately for Rich, disagrees with what Rich claims.

If you want to read filament voltage data, here is a web page with links to the actual Eimac publications:

http://www.w8ji.com/filament_voltage_life.htm

Eimac links    http://www.w8ji.com/Vacuum%20Tubes/CPI%20AB-18%20New%20v2.pdf    and direct quotes from Eimac state:

"NOTE: If the filament voltage cannot be regulated to within ± 3%, the filament should always be operated at the rated nominal voltage specified on the data sheet.

It should be noted that there is a danger to operating the emitter too much on the “cold” temperature side. It may become “poisoned.” A cold filament acts as a getter; that is, it attracts contaminants. When a contaminant becomes attached to the surface of the emitter, the affected area of the emitter is rendered inactive, causing loss of emission. "

and Eimac says:

"When a noticeable change occurs in the output power or if the distortion level changes, the de-rating procedure must stop. Obviously, operation at and beyond this point is unwise since there is no margin allowed for a drop in line voltage. The voltage should be raised 0.2V above the critical voltage at which changes are observed to occur. Finally, recheck power output or distortion to see if they are acceptable at the chosen filament voltage level. Recheck again after 24 hours to determine if emission is stable and that the desired performance is maintained. If performance is not repeatable, the derating procedure must be repeated. Continuing the Program The filament voltage should be held at the properly de-rated level as long as minimum power or maximum distortion requirements are met. Filament voltage can be raised to reestablish minimum requirements as necessary. This procedure will yield results similar to those shown in the illustration (Figure eight), to achieve as much as 10% to 15% additional life extension. When it becomes necessary to start increasing the filament voltage in order to maintain the same power output, it is time to order a new tube. Filament voltage can be increased as long as the increase results in maintaining minimum level requirements. However, when a voltage increase fails to result in meeting output level requirements, filament emission must be considered inadequate and the tube should be replaced. Don’t discard it or sell it for scrap! Put it on the shelf and save it. It will serve as a good emergency spare and may come in handy some day. Also, in AM transmitters, a low-emission RF amplifier tube can be shifted to modulator use where the peak filament emission requirement is not as severe. "

end of Eimac's quoted text.

Eimac ACTUALLY says:

1.)    DO NOT derate the filament if you cannot regulate the filament

2.)  If you derate, you must measure either output power reduction or distortion and set the filament 0.2 volts above the critical point, and monitor that point for changes in operation

3.) Eimac says if you do this complex filament management right and wring things out to the end, you can get 10-15% more life.

None of it says anything remotely similar to whart Rich claims, and everyone can read it for themselves.

Eimac says NOTHING like Rich claims they say, so he is intentionally misleading people. Worse than that, if Rich's instructions are followed, you can damage your tubes faster than leaving them at higher voltage, and can trash the bands with splatter. This not only ruins people's tubes, it ruins out bands with splatter.

By the way, I changed a two-year old pair of 3-500Z's out in an amplifier that was loaded with Rich's mods, because the tubes were weak. His changes don't do a thing to increase life or reliablility, and increase the splatter and reduce the output. 

73 Tom


[/quote]
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AG6K
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« Reply #138 on: November 18, 2011, 08:17:36 AM »

Eimac's Application Bulletin AB-18 covers filament voltage and its affect on tube life. My understanding is that there are significant tradeoffs involved and too low a filament voltage can be a real problem. Tom R. and few others have written extensively about this subject and how it pertains to SSB and ICAS applications. It's good reading and puts the filament voltage subject into context.

However, on page 163 of Eimac's Care and Feeding of Power Grid Tubes, it says: "Theoretically a 3% increase in filament voltage will result in a 20 Kelvin increase in temperature, a 20% increase in peak emission, and a 50% decrease in life due to carbon loss. This, of course, works the other way, too." I understand that this statement is taken out of context and comes with many caveats, but it is where Rich say it is for people to use or misuse as they see fit.

Sam
  Thanks for digging this one up Sam.  I was pretty sure that the –3% fil-V = double the emissive life was correct but I couldn't find it.  Apparently Mr. Rauch couldn't find it either so I am pretty sure that he will be delighted with your find.
cheers
Rich, ag6k

























































































0........
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AG6K
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« Reply #139 on: November 18, 2011, 08:35:11 AM »

Eimac's Application Bulletin AB-18 covers filament voltage and its affect on tube life. My understanding is that there are significant tradeoffs involved and too low a filament voltage can be a real problem.

  According to Econco Broadcast Services, operating the filament below the point where PEP begins to drop off can cause premature emission drop provided there are air molecules inside the tube,  However, by raising filament V to normal for a few hours emission can be restored to normal.  The rule is:  do not operate the filament at less than 2% above the point where PEP or anode-I begins to decrease -- but if you do the damage is easy to undo. 
•••  Rich, ag6k


Quote
Tom R. and few others have written extensively about this subject and how it pertains to SSB and ICAS applications. It's good reading and puts the filament voltage subject into context.

However, on page 163 of Eimac's Care and Feeding of Power Grid Tubes, it says: "Theoretically a 3% increase in filament voltage will result in a 20 Kelvin increase in temperature, a 20% increase in peak emission, and a 50% decrease in life due to carbon loss. This, of course, works the other way, too." I understand that this statement is taken out of context and comes with many caveats, but it is where Rich say it is for people to use or misuse as they see fit.

Sam
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WB6BYU
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« Reply #140 on: November 18, 2011, 09:02:40 AM »

Quote from: G3TXQ
I'm a simple soul, and all this talk of photons etc makes my head spin Smiley

So, I looked at a simple modelling experiment. I modelled a 20m, centre-fed, Inverted-V, half-wave dipole with its apex at 35ft and the two ends at 25ft. ...

...What could explain that other than that the centre of the dipole, where the current is highest, makes more contribution to the Far-Field radiation than do the ends?


But Steve, you know that any good Conspiracy Theorist will simply point out that the
modeling software is based on the incorrect assumptions, so only promulgates the fallacy.


What we need is a simple physical experiment.  Like this:

Make a bent dipole in a Z shape:  say 1/8 wave up, 1/4 wave horizontal, and another
1/8 wave up.    Feed it in the center as normal.  I'd use a small signal source so there
is no feedline to confuse matters.

Now, looking broadside at the antenna, if radiation is just from the center the radiation
should be horizontally polarized.  If it is equal from all portions of the antenna it should
be slant polarized at 45 degrees.  Each side of the argument can calculate exactly what
the resulting polarization should be according to their view of the world.

Then stand back a few wavelengths with a 3-element yagi pointed at the antenna and
rotate it around its boom to determine the polarization of the resulting signal.  This
doesn't require an accurate measurement of signal strength, just a sufficient relative
reading to find the null.  (Presuming, of course, that both sides can agree on the
polarization of a 3-element yagi.)  One should be able to detect the null within 10
degrees.

If there is concern about the effect of ground (which each side also could include in
their calculations) then rotate the source antenna about its axis and repeat the test.

Or, if only a vertical antenna is available for receiving, rotate the antenna under test
for a null.

You could also adjust the relative horizontal and vertical lengths of the elements so
that, for example, the two models predicted polarizations on either side of the 45 degree
mark.


This is an experiment that almost anyone can do using a small crystal oscillator with a
harmonic on VHF and a receiver that can pick it up, along with a reference antenna with
a known polarization.  I happen to have several wire 2m dipoles with signal sources, an
assortment of beam antennas, and some receivers designed to indicate relative signal
strength, so it might take me 10 minutes (mostly to find everything in the barn.)


Then we just need the supporter(s) of each theory to predict the expected polarization
of the bent antenna, and we can quickly resolve this matter instead of wasting bandwidth
arguing about it.
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G3TXQ
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« Reply #141 on: November 18, 2011, 09:36:25 AM »

But Steve, you know that any good Conspiracy Theorist will simply point out that the
modeling software is based on the incorrect assumptions, so only promulgates the fallacy.
Dale,

You're right - I forgot that the modelling software is based on incorrect assumptions. I guess that the excellent correlation between my measured Hexbeam radiation patterns and those predicted by EZNEC is just serendipity Smiley

Steve G3TXQ
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AG6K
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Posts: 1




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« Reply #142 on: November 18, 2011, 10:40:01 AM »




So here is the real point, is it worth the time to point this all out? Or does everyone realize it all? Are the bad theories doing damage, or are they no concern? In my experience, gross mistakes in theory seriously hurt amateur radio. There are baluns popularly accepted as baluns that don't work, and actually force unbalance. There are baluns on the input of tuners.

  What other way is there to feed a balanced-L tuner from a 50-ohm unbalanced output from a transceiver. or an amplifier?


Quote
There are amplifier tubes ruined by modifications like reducing filament voltage outside, or near the lower limit, of allowable voltage.  

  Not according to Econco Broadcast Services, at least for Th-W filament tubes.

Quote
73 Tom

Quote
I agree, this stuff does inflict damage in the long run.  I believe we've all known someone who had alternate theories about Electronics and Physics.  It's an interesting personality type in that they believe that they have found flaws in scientific theories and the rest of us are just not smart enough to understand, so we stick with the dogma that Newton, Maxwell, Einstein, etc have left us.

  Einstein's Theory of General Relativity upset Newtonian physics

Quote
Of course this personality type can never provide proof for their theories.

  Einstein was eventually proved right by Arthur Stanley Eddington during the 1919 solar eclipse. 

Quote
So when faced with rational arguments, they don't participate and then begin spewing personal attacks or just ignore evidence that's contrary to their theories.  It's as if some of their scientific knowledge came from Star Trek.

This thread and the cosmic ray thread have been interesting from the perspective of watching how the ego clings to nonsense.  But in the long run, it's not good for amateur radio.

  so amateur radio operators should not possess a Geiger-Muller counter?
Rich, ag6k
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W8JI
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Posts: 9296


WWW

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« Reply #143 on: November 18, 2011, 05:02:44 PM »

  Eimac states that each 3% increase in filament potential above that which produces full PEP decreases the emissive life of the tungsten dicarbide layer by 50%. 

The very first sentence Rich posted excludes his formula, and telling people to set voltage to 4.8 volts or any other fixed voltage. The key words Rich ignores are:
 
Quote
above that which produces full PEP

This is what happens when someone chooses what part of a long text he wants to use, and discards the rest.

If we include ALL of the text it is plain none of it allows blind application of some arbitrarily assigned voltage chosen by AG6K, or anyone else.

As a matter of fact Eimac actually never intended that theoretical statement to be directly applied to anything. The actual full original filament management text is here:

http://www.bext.com/filament.htm


The newest revision is here:

http://www.w8ji.com/Vacuum%20Tubes/CPI%20AB-18%20New%20v2.pdf

The full Eimac CPI text on filament management disagrees with Rich.

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AG6K
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« Reply #144 on: November 18, 2011, 06:19:23 PM »



Quote
  Eimac states that each 3% increase in filament potential above that which produces full PEP decreases the emissive life of the tungsten dicarbide layer by 50%.  If one puts this relationship into a math formula, one arrives at (V2/V1)23.4. . . Checking the formula:  ((1.0/1.03)23.4= 0.500 . Real world example:  A stock TL-922 being operated from 240VAC mains:  The filament V at the sockets is 5.31v.  The max/min filament V rating is 5.25v/4.75v.  If the filament V is reduced from 5.31v to 4.8v, the emissive life is (5.31v/4.8v)23.4 = 10.6 x what it would have been at 5.31v.
  This formula was included in the  article "The Nearly Perfect Amplifier" which was published in the January, 1994 issue of QST Magazine.
cheers Scott
Rich, ag6k


I had previously read the passage that it sounds like you're referencing for your formula in the CARE AND FEEDING OF POWER GRID TUBES.  I think you're taking an unjustified leap to apply the data provided in the manner you have.

73,
Scott

  Leap?  Eimac makes power grid tubes with Th-W filaments and that is what the formula:  Emissive-life = (V2/V1)23.4 applies to Scott.
••• Rich, ag6k
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AG6K
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« Reply #145 on: November 18, 2011, 07:02:50 PM »

  Eimac states that each 3% increase in filament potential above that which produces full PEP decreases the emissive life of the tungsten dicarbide layer by 50%. 

The very first sentence Rich posted excludes his formula, and telling people to set voltage to 4.8 volts or any other fixed voltage. The key words Rich ignores are:
 
Quote
above that which produces full PEP

This is what happens when someone chooses what part of a long text he wants to use, and discards the rest.

   p.163 CARE AND FEEDING OF POWER GRID TUBES,PAR.  4:  ""Theoretically a 3% increase in filament voltage will result in a 20º Kelvin increase in temperature, a 20% increase in peak emission, and a 50% decrease in life due to carbon loss.  This of course works the other way too.  For a small decrease in temperature and peak emission, life of the carbide layer cam be increased by a substantial percentage."

Example:  One of the Amperex 3-400Z tubes in my SB-220 was mfg in 1967 and the other one was mfg in 1980.  The filament V on Rx is c. 4.8v.   Output is normal and they don't splatter any more than new tubes.
••• Rich, ag6k

"You can fool some of the people all of the time, and all of the people some of the time, but you can not fool all of the people all of the time."    Abraham Lincoln
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W8JI
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WWW

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« Reply #146 on: November 18, 2011, 07:50:13 PM »

Show us a picture of your test set or a print of the IM data for your tubes, and tell us how you measured IMD to know that.

Here are actual measurements:


http://www.w8ji.com/filament_voltage_life.htm

-35dB PEP 3rd order, 3000 volts anode. 850 W PEP target

Type Min filament V RMS PEP @ -35 dB IM3
China     5.25       800
Machlett (1) 4.8      850
Eimac 4.7      850
Triton 4.7     850
Machlett (2) 4.7      850
Amperex 4.5      850


My bet is you cannot measure IMD and never have, because you do not have the equipment or test setup. I suspect this  because I have measured IMD as filament voltage is changed, and found in amateur service typical power that allows for wear, only a few types are suitable at the voltages you tell people to run.  

If you actually bother to measure anything, you would have stopped telling people to set everything at some fixed low voltage years ago.

 
« Last Edit: November 18, 2011, 07:55:36 PM by W8JI » Logged
W7SMJ
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Posts: 120




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« Reply #147 on: November 18, 2011, 10:12:08 PM »

  Leap?  Eimac makes power grid tubes with Th-W filaments and that is what the formula:  Emissive-life = (V2/V1)23.4 applies to Scott.
••• Rich, ag6k

Rich,

That's not what Eimac said.  You have quoted the reference several times yourself.  If Eimac felt that Emissive-life = (V2/V1)23.4 then that's what they would have said.  They would have included your formula.  They didn't.  You are also leaving out the phrase "In theory".  Note that they didn't say "In practice".  They also said a 3% increase in filament voltage results in a 20 degree K temperature increase.  What about a 4% increase in filament voltage?  How about a 5% increase in filament voltage?  For that matter, what does a 3% decrease in filament voltage do to the filament temperature?  They didn't say...

In any case I think I will have to respectfully disagree with you that what Eimac wrote can be extrapolated to Emissive-life = (V2/V1)23.4.

73,
Scott 
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AG6K
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« Reply #148 on: November 19, 2011, 04:54:25 AM »

  Leap?  Eimac makes power grid tubes with Th-W filaments and that is what the formula:  Emissive-life = (V2/V1)23.4 applies to Scott.
••• Rich, ag6k

Rich,

That's not what Eimac said.  You have quoted the reference several times yourself.  If Eimac felt that Emissive-life = (V2/V1)23.4 then that's what they would have said. 


  Eimac said "theoretically a 3% increase in filament voltage will result in a 20º Kelvin increase in filament temperature, a 20% increase in peak emission, and a 50% decrease in life due to carbon loss."  Expressing this in a formula results in: Relative Life = V2/V1)23.4.  Verifying the formula:  (1.00v/1.03v)23.4 = 0.500.  Are you okay with the verification Scott?
•••  Rich, ag6k


Quote
They would have included your formula.  They didn't.  You are also leaving out the phrase "In theory".  Note that they didn't say "In practice".  They also said a 3% increase in filament voltage results in a 20 degree K temperature increase.  What about a 4% increase in filament voltage?  How about a 5% increase in filament voltage?  For that matter, what does a 3% decrease in filament voltage do to the filament temperature?  They didn't say...

In any case I think I will have to respectfully disagree with you that what Eimac wrote can be extrapolated to Emissive-life = (V2/V1)23.4.

73,
Scott 
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N2EY
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« Reply #149 on: November 19, 2011, 05:22:06 AM »

Eimac said "theoretically a 3% increase in filament voltage will result in a 20º Kelvin increase in filament temperature, a 20% increase in peak emission, and a 50% decrease in life due to carbon loss." 

That's a small quote from a much larger text in which context is most important.

Expressing this in a formula results in: Relative Life = V2/V1)23.4.

But over what limits is the formula accurate? It is not always accurate to look at a very small data range and extrapolate into a wide-range formula. But that's what you're doing.

More important, Eimac states categorically that reduction in filament voltage should only be done if 1) the point of IMD degradation can be accurately measured, 2) the tube(s) have been "broken in" for a couple of hundred hours, and 3) the filament voltage can be carefully regulated and accurately measured.

What this says to me is that, in an amateur-radio setup, I should only attempt life-extension by filament-voltage reduction if I have the required test equipment and know how to use it, plus an amplifier with a regulated or at least controlled filament supply.

And if I decide to use filament-voltage-reduction, I should evaluate the IMD performance at least every time I change bands, because operating conditions may be different on different bands.

It seems very clear to me that the Eimac verbiage was intended for applications where tubes are operated under the same conditons for long periods of time, such as broadcasting.

One of the biggest mistakes being made is the selective quotation of a small part of a big text, thereby losing the context and qualifications of the original.

73 de Jim, N2EY
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