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Author Topic: 811A Tube lifespan  (Read 16831 times)
KB1LKR
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« Reply #15 on: September 11, 2011, 10:23:13 AM »

"Isn't there some life expectation from the manufacturers?"

You'd have to specify conditions for test, e.g. (RCA data, 4/1963) steady AB2 operation at CCS limits (1250V plate, 45W dissipation, 120W PEP out (no anode color) or ICAS 1500V, 65W diss. 160W out ("barely perceptible" anode color)... plus you'd have to define a quantifiable failure criteria: e.g. how much loss in initial performance; while the CCS test might have real world value for a fix RF (or AF) amp installation, the ICAS data wouldn't account for the intermittent nature of use w/ off-on cycling occasional tuneup operation under adverse conditions, so might give a best case.

Of course now, RCA JAN spec data from the '50's or '60's would be meaningless for todays imports even if you could find it.

New or old, drive'm easy and tune'm quick and take what you get.
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W8JX
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« Reply #16 on: September 11, 2011, 11:06:51 AM »

There is a myth that increasing airflow increases life, but very few tubes except external anode tubes can be hurt by low airflow other than glass melting or seals failing. If you take time to read Eimac's and other manufacturer's literature you will see the only tubes having increased dissipation with increased airflow are external anode tubes.

I disagree and so does Eimac Tom because their 3-500Z and other such tubes were designed to have a chimney of their design around tubes with air forced up from base for rated dissipation. (like AL-82 PROPERLY uses and AL-80B does not) Not just with tube just stuck in a socket with a little air blown over it. You "should" be last person I need to tell this too. Sure you can run them without chimneys but you will not safely achieve rated dissipation ratings.

The 811 has long thin leads, and is isolated in a vacuum. There is very little you can do to decrease anode temperature short of increasing anode surface area. If you get an airflow problem it will show as melted glass, not a melted anode.

Not true again Tom. Granted these tubes are not as efficient at transferring heat because they do it via thermal radiation across a vacuum but with even here, the cooler the surroundings the more heat that will be removed from tube. Granted not as efficient as a external anode but it helps. Your words suggest that those tubes could in effect be in a sealed box and nearly last as long as ones with forced air cooling. Not so Tom and as learned as you are you should know better.

It's a 60-65 watt rated anode. We are stuck with that if the tube is convection cooled or placed in a hurricane force wind. A 3CX3000 or any other external anode will move all over the place in dissipation rating with airflow, not a 572 or 811. Read the spec sheets, they are actually designed for convection cooling.

It you read specs Tom the ratings are for a single tube in a open chassis and lots of convective cooling possible. Not in a closed sealed chassis nor in installations with two or more tubes on same type mounted close together the reduces thermal dissipation possible without the aid of forced air cooling to reset balance.  And again Tom with thermal radiation from a vacuum tube, the cooler the air surrounding a envelope, the more heat transferred. Not as much as a external anode tube but an improvement none the less.
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W8JI
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« Reply #17 on: September 11, 2011, 01:01:30 PM »

I spent weeks doing thermal tests. I'm not guessing, or making anything up.

You can run 200 CFM across the tubes and life will not change a measurable amount. That is because of HOW the heat gets out of the tube. It's an absolute myth that blowing more air across an 811 or 572 will extend the life.

I'm not sure where that idea comes from, but it isn't based on how the tubes work.

It also is not true that the 30L1 runs more airflow. 

The cooling in a 3-500Z is all about seal temperatures. This is because the tube has THICK leads for the anode and base pins, and has short leads. Thermal resistance is much lower from the elements to the seals in a 3-500Z. It is nothing at all like an 811A or 572B. Even so, the only thing the air does in the 3-500 tantalum anode tube is keep the seals and glass below failure temperature. There is almost no change in anode heat for the same dissipation if you blow 100 CFM across the anode, or 10 CFM. The only significant change is in seal temperature.

It may be disappointing, but that is just how that style of cooling works. You'd make a much bigger change with a can of black spray paint on shiny surroundings then with more air.
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W8JX
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« Reply #18 on: September 11, 2011, 04:23:49 PM »

I spent weeks doing thermal tests. I'm not guessing, or making anything up.

Quality of tests is in question. I used to work with flight test and they left no stone unturned when testing. Vacuum loose heat by thermal radiation. Surrounding area MUST absorb it of it is reflected back to tube. When you have multiple tubes together they can radiate heat into one another and lower maximum safe dissipation. Air flow restores balance.

You can run 200 CFM across the tubes and life will not change a measurable amount. That is because of HOW the heat gets out of the tube. It's an absolute myth that blowing more air across an 811 or 572 will extend the life.

No myth to it Tom. I guess you do not understand thermodynamics and heat by radiation. Cooler the surrounding air, the more heat tube can loose. Maybe only 10% or 15% or so but it WILL help. Tell you what disconnect fan on your tube amps and see how quickly tube plates melt on say a 811.

I'm not sure where that idea comes from, but it isn't based on how the tubes work.

Again you do not understand it. Place tubes in a oven they will be able to loose less heat verse a place with some cool airflow. You are not going to double ratings but you will help.


It also is not true that the 30L1 runs more airflow. 

Maybe but it does not just have a fan stuck in side of a big open box blowing a little air at tubes.

The cooling in a 3-500Z is all about seal temperatures. This is because the tube has THICK leads for the anode and base pins, and has short leads. Thermal resistance is much lower from the elements to the seals in a 3-500Z. It is nothing at all like an 811A or 572B. Even so, the only thing the air does in the 3-500 tantalum anode tube is keep the seals and glass below failure temperature. There is almost no change in anode heat for the same dissipation if you blow 100 CFM across the anode, or 10 CFM. The only significant change is in seal temperature.

I guess Eimac wasted time making chimneys huh. even wall of cool air flow around tube will help get heat away. I find it amazing you think otherwise.

It may be disappointing, but that is just how that style of cooling works. You'd make a much bigger change with a can of black spray paint on shiny surroundings then with more air.

Black paint will not help on items that are not generating heat. It does help on items that make heat. Thermal radiation of heat is most effective into cool surroundings.

BTW Tom even cold items have heat energy because there really is not such thing as cold as it only has a lower level of heat in it. Short of absolute zero everything has some heat in it and is radiating it. Radiant heat transfers energy in the form of heat to a median with a lower heat energy level. Greater the temperature differential and mass of cooler median the more energy is transferred. By using forced air cooling you in effect increase mass around tube due to it constantly being replaced and enhance heat transfer.   
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W8JI
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« Reply #19 on: September 11, 2011, 05:26:43 PM »

W8JX,

There are so many things wrong with what you are saying, it really isn't worth going through it all.

Much of it I can't even understand, like:

Quote
Vacuum loose heat by thermal radiation.
 

What does that mean? A vacuum has no heat, and I suppose by "loose" you mean "lose". By thermal radiation I suppose you mean electromagnetic radiation, mostly in the infrared region.

Then of course we have this:

Quote
Black paint will not help on items that are not generating heat. It does help on items that make heat. Thermal radiation of heat is most effective into cool surroundings.


I guess what you are saying is if we have a black background or black body, it does not absorb infrared radiation. So silver or shiny does not reflect a large portion of IR, and black does not absorb it.

I think most people would disagree with that, especially those who have worn a black shirt in from of a large IR heat source.

Not much of what you said is accurate, much of it is obviously inaccurate. 

73 Tom
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N2EY
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« Reply #20 on: September 11, 2011, 05:30:45 PM »

Here's how I understand glass envelope tube cooling works:

Some of the heat inside the tube is radiated to the surroundings. If the surroundings are good absorbers of radiant heat, they get warmer. If they are good reflectors of radiant heat, they reflect the heat back into the tube - which isn't a good thing.

Some of the heat inside the tube is conducted out via the leads and other tube parts. This is a particular concern in tubes with short, fat leads like the 3-500Z. because the tube seals can get too hot if proper steps are not taken.

Some of the radiant heat inside the tube is absorbed by the glass envelope and the surrounding outside air as it passes through. This amounts to very little actual heat because clear substances don't absorb all that much - if they did, they wouldn't be clear.

In tubes like the 3-500Z, the main reason for forced-air and chimneys is to keep the tube seals cool. A secondary benefit is cooling the whole tube, but the main issue is the big pins coming through the glass. This is spelled out in "Care and Feeding..."

Of course it doesn't hurt to have air flowing through the equipment to reduce the temperature of ALL the components, particularly ones like electrolytic caps in the power supply, silicon diodes, etc.

73 de Jim, N2EY
« Last Edit: September 11, 2011, 05:32:21 PM by N2EY » Logged
W8JI
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« Reply #21 on: September 11, 2011, 06:18:45 PM »

Jim,

What you wrote below is absolutely correct.

I went through all of this for at least the last 30 years. :-) Seal temperature was critical for maintaining the 3-500Z warranty.

Airflow over the tube does not noticeably affect tube anode cooling, contrary to what W8JX thinks. All it really does is keep the seals within limits, and secondarily the envelope.  These is a little cooling, but the majority by far is radiation.

The 811 and 572 have even less conduction cooling.

If we could just run the tubes without a vacuum, then more air across the envelopes would help a great deal.  Every time I try that though the power output goes way down. :-)

73 Tom

Here's how I understand glass envelope tube cooling works:

Some of the heat inside the tube is radiated to the surroundings. If the surroundings are good absorbers of radiant heat, they get warmer. If they are good reflectors of radiant heat, they reflect the heat back into the tube - which isn't a good thing.

Some of the heat inside the tube is conducted out via the leads and other tube parts. This is a particular concern in tubes with short, fat leads like the 3-500Z. because the tube seals can get too hot if proper steps are not taken.

Some of the radiant heat inside the tube is absorbed by the glass envelope and the surrounding outside air as it passes through. This amounts to very little actual heat because clear substances don't absorb all that much - if they did, they wouldn't be clear.

In tubes like the 3-500Z, the main reason for forced-air and chimneys is to keep the tube seals cool. A secondary benefit is cooling the whole tube, but the main issue is the big pins coming through the glass. This is spelled out in "Care and Feeding..."

Of course it doesn't hurt to have air flowing through the equipment to reduce the temperature of ALL the components, particularly ones like electrolytic caps in the power supply, silicon diodes, etc.

73 de Jim, N2EY

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W9KDX
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« Reply #22 on: September 11, 2011, 06:22:35 PM »

OK, I get it.  Power is not the problem, heat is the problem.  Let me summarize what you guys have said so I don't miss anything.  And I was kidding about "lasting forever".  I know better, but I really want to use this thing gently and safely so...

1. Don't hold the key down more than a few seconds during tuning and let it cool off.

2. Check the frequency before I tune. I really knew this before and I always check for anything.

3. Once I have it tuned, reduce output from the transceiver to reduce output from the amp. Don't re-tune.

4. Keep my transceiver power low, like 50-70 watts tops.

One poster mentioned a need to re-tune if I change frequencies too much.  I am only on 20 and 40 meters.  Do these bands have enough difference (within the band of course) to require re-tuning?

Other than the initial tune up, done carefully of course, if I keep record of the setting at 20 meters and 40 meters, do I need to re-tune over time or do I need to re-tune when I reduce wattage at the transceiver?

Given heat as a problem, in SSB mode is there anything I can do to reduce heat in my operation or in any setting on the amp?

Thanks again guys.  Valuable information.  If I missed anything, let me know, I am not sure about "duty cycle" and how my SSB usage could impact it.

Lastly, the 811H Ameritron is rather simpy in the manual department.  I have watched their You Tube videos a few times and it makes sense.  Is there anything there I need to do differently?
« Last Edit: September 11, 2011, 06:33:16 PM by KD0PLD » Logged

Sam
W9KDX
W8JI
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« Reply #23 on: September 11, 2011, 06:33:36 PM »


One poster mentioned a need to re-tune if I change frequencies too much.  I am only on 20 and 40 meters.  Do these bands have enough difference (within the band of course) to require re-tuning?

It depends on how far you move and how the antenna works as you change frequency. Unless you have a real narrow antenna, you should be able to move about 1% up or down without worry. On 40 meters that's 70 kHz up or 70 kHz down.   

I have a provisional patent on a tuning aid that will solve most problems like this. It allows checking tuning while just talking or sending normal CW. Too bad tubes are on the way out. :-)     

Quote
Other than the initial tune up, done carefully of course, if I keep record of the setting at 20 meters and 40 meters, do I need to re-tune over time or do I need to re-tune when I reduce wattage at the transceiver?

Follow the manual. Do not retune at lower power.

I reset my amps with a tuning chart. As long as SWR stays the same so will the settings. You should notice if something is wrong on the power meter and grid meter.

Quote
Given heat as a problem, in SSB mode is there anything I can do to reduce heat in my operation or in any setting on the amp?

Don't run heavy ALC or processing.
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W9KDX
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« Reply #24 on: September 11, 2011, 06:45:47 PM »


One poster mentioned a need to re-tune if I change frequencies too much.  I am only on 20 and 40 meters.  Do these bands have enough difference (within the band of course) to require re-tuning?

It depends on how far you move and how the antenna works as you change frequency. Unless you have a real narrow antenna, you should be able to move about 1% up or down without worry. On 40 meters that's 70 kHz up or 70 kHz down.  

I have a provisional patent on a tuning aid that will solve most problems like this. It allows checking tuning while just talking or sending normal CW. Too bad tubes are on the way out. :-)    

Quote
Other than the initial tune up, done carefully of course, if I keep record of the setting at 20 meters and 40 meters, do I need to re-tune over time or do I need to re-tune when I reduce wattage at the transceiver?

Follow the manual. Do not retune at lower power.

I reset my amps with a tuning chart. As long as SWR stays the same so will the settings. You should notice if something is wrong on the power meter and grid meter.

Quote
Given heat as a problem, in SSB mode is there anything I can do to reduce heat in my operation or in any setting on the amp?

Don't run heavy ALC or processing.


I'm not that good at this yet.  How would I run "heavy ALC or processing"?  Also, I read your web site on tuning and the section on ALC overshoot has me concerned.  Does the Yeasu FT-950 have this problem.

Part of what you suggest is advancing the loading control a reasonable amount beyond (further open) the actual maximum output power setting.  I am guessing at what this is, I think it has to do with the "dip".  Given that I can't be safe setting my 950 at 50 watts, I want to make sure I do this right.

What will I see on the meters if I go too far in frequency change and need to re-tune?

Thanks a ton!
« Last Edit: September 11, 2011, 06:49:19 PM by KD0PLD » Logged

Sam
W9KDX
W8JX
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« Reply #25 on: September 11, 2011, 07:07:18 PM »

W8JX,

There are so many things wrong with what you are saying, it really isn't worth going through it all.

Much of it I can't even understand, like:

Vacuum loose heat by thermal radiation.
 

Cannot read either. Thermal radiation and conduct heat thru a vacuum Tom you have built amps but the science here is beyond you.

What does that mean? A vacuum has no heat, and I suppose by "loose" you mean "lose". By thermal radiation I suppose you mean electromagnetic radiation, mostly in the infrared region.

Where did I say Electro Magnetic Radiation Tom?Huh  Also Tom a vacuum is a good conduit for thermal radiation and even a vacuum has thermal energy. In space (where vacuum is deeper than is a tube) there are still atoms and molecules that hold heat energy there is just a lot less of them


Then of course we have this:

"Black paint will not help on items that are not generating heat. It does help on items that make heat. Thermal radiation of heat is most effective into cool surroundings. "

I guess what you are saying is if we have a black background or black body, it does not absorb infrared radiation. So silver or shiny does not reflect a large portion of IR, and black does not absorb it.

I think most people would disagree with that, especially those who have worn a black shirt in from of a large IR heat source.

You like to shift around and try to change focus. Thermal energy always flows from higher temperature/energy level to a lower one. Simple physics. On the black shirt/black paint, we cannot paint a tube black and a black chassis is not going to do better than positive air flow and may make amp run warmer as more heat would be absorbed my chassis rather than vented out.

Not much of what you said is accurate, much of it is obviously inaccurate. 
73 Tom

Tom you are one with ducks not in a row on this on not me. You are a smart guy on many amp electrical problems without question but your expertise it seems does not include thermal energy transfers.
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N2EY
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« Reply #26 on: September 11, 2011, 07:49:39 PM »

Thermal radiation and conduct heat thru a vacuum Tom you have built amps but the science here is beyond you.

I have no idea what you are trying to say there.

a vacuum is a good conduit for thermal radiation and even a vacuum has thermal energy. In space (where vacuum is deeper than is a tube) there are still atoms and molecules that hold heat energy there is just a lot less of them

There are so few atoms and molecules in space or in a good tube that they play no real role in thermal energy transfer. The overwhelming way that thermal energy is transferred through a vacuum is by radiation. In a tube, conduction through the wires is the other main path.

Thermal energy always flows from higher temperature/energy level to a lower one. Simple physics.

That's true.

On the black shirt/black paint, we cannot paint a tube black and a black chassis is not going to do better than positive air flow and may make amp run warmer as more heat would be absorbed my chassis rather than vented out.

I don't think you understand.

Take two identical pieces of shiny aluminum sheet - same thickness, same size. Say a foot square and 1/16 inch thick.

Paint one flat black, leave the other natural aluminum.

Place them both out in the sun on a sunny day, in such a way that they both get the same angle and amount of sunlight.

Leave them out in the sun for an hour and see which gets hotter.

Dollars to donuts it's the black one, because it absorbs more heat and the natural aluminum one reflects it.

The same thing happens inside an amplifier. An amplifier enclosure painted black on the inside will absorb heat radiated by glass tubes while a shiny aluminum one will reflect it back into them.

This isn't new stuff. Way back in July 1968 there was an article in QST about using sweep tubes in amplifiers, and forced-air cooling. They mentioned how to make tube  chimneys from tin cans - and how any such chimneys had to be painted flat black to avoid reflecting heat back into the tube.

None of this means forced air is a bad thing.

73 de Jim, N2EY
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W8JI
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« Reply #27 on: September 12, 2011, 02:58:15 AM »

Anyway, in summary:

1.) The primary heat transfer mechanism in an 811 (or even 3-500Z) is via electromagnetic radiation through the vacuum. The frequency range is primarily infrared. Conducted heat is especially low in a tube with long thin leads like an 811.

2.) Once there is enough air flowing over the envelope to keep seals and envelope well below ratings, any additional air will not significantly impact tube life.

3.) Forced air external anode tubes primarily cool by direct air-to-anode contact. Increasing airflow at a given temperature directly increases dissipation rating. They still won't last longer from more airflow, unless the seals or anode temperature are getting near limits.

73 Tom
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KA5N
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« Reply #28 on: September 12, 2011, 03:38:42 AM »

I wonder how many newbie hams, after reading this thread, began to wonder why they didn't take up Civil War reenactments instead of ham radio.

Allen
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N2EY
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« Reply #29 on: September 12, 2011, 04:05:50 AM »

I wonder how many newbie hams, after reading this thread, began to wonder why they didn't take up Civil War reenactments instead of ham radio.

Interesting comment!

I think it's important to get stuff right, because the alternative is expensive and frustrating.

73 de Jim, N2EY
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