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Author Topic: Tube heat dissipation  (Read 27168 times)
W8JX
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« Reply #30 on: August 14, 2013, 08:35:51 PM »

I used a SB200 for field day once and it got pretty warm in that duty cycle and could stand extra cooling in that usage.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
G3RZP
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« Reply #31 on: August 15, 2013, 01:56:24 AM »

AD4U,

Not so much your side of the pond, but the British KW1000 (two 572B) and its little brother, the KW600 (one 572B) date from the 1960s and  there are quite a few of them in use over here.

Many with the original Cetron 572Bs in them as well! Those Cetron tubes were very good.
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AD4U
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« Reply #32 on: August 15, 2013, 06:22:58 AM »

I used a SB200 for field day once and it got pretty warm in that duty cycle and could stand extra cooling in that usage.

I agree.  IMO the SB 200 was never designed to be a contest type amp, even though it was advertised to operate 100% duty cycle on SSB and (I think) 50% duty cycle on CW with max transmit time of 30 minutes.  That is a long CW QSO without a break.  Max continuous key-down time was 5 minutes.  Any nut should be able to get it tuned up in that amount of time.   Cry   I guess a hot and heavy field day operation can easily exceed the CW ratings.  In this case additional cooling would probably be in order.  So often people get hung up on cooling the tubes, but don't forget that heat generated in the power transformer must be dissipated as well.

I am not trying to get into a pee'ing contest with anyone.  All I was posting was my personal experience based on 42 years operating a SB 200 and some 35 years repairing boat anchor HAM gear.  I have someone's SB 200 in the shop right now, but the problem is not in the tubes or the PS.  The HV filter caps are going "south" and the owner is not comfortable replacing them.

I think the SB 200 was introduced by Heathkit in the mid 1960's.  If so then some of the earlier ones are almost 50 years old.  The fact that so many are still in use speaks volumes.  As I posted earlier (other than the Collins 30L1) I am not aware of any other amp that has stood the test of almost 50 years (except as posted by G3RZP) and is still in such wide-spread use. 

I am sure there have been problems with SB 200 amps, but WHEN OPERATED WITHIN THE PUBLISHED RATINGS, I have never heard of a single SB 200 transformer failure or a melt-down of any Cetron 572B tubes.  The original Cetron 572B tubes in mine are still going strong after 42 years.

Dick  AD4U
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KE3WD
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« Reply #33 on: August 15, 2013, 06:27:05 AM »


Throw a muffin fan on the thing for Field Day ops.  
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W8JX
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« Reply #34 on: August 15, 2013, 06:43:33 AM »


Throw a muffin fan on the thing for Field Day ops.  

Actually if I used one again I would make a cover with a muffin fan that would draw air from tube compartment and power supply area.
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KD0REQ
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« Reply #35 on: August 15, 2013, 02:10:50 PM »

KE3WD is right on... the simplest, quickest solution is to get a muffin fan, put some bumper feet over the screw holes, and set it on top of the amp blowing air straight up.  no holes, no damage, no paint scrapes, look inside periodically to make sure the anodes get at least dull red on ragchews, forget about it until it won't load any more.

or until your heirs and assigns can't get it to load any more.
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KE3WD
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« Reply #36 on: August 15, 2013, 02:48:57 PM »

I found with my old 30-L1s that using the muffin fan to blow downwards, thus slightly pressurizing the cabinet, would cool it a bit better. 

But either direction is better than no fan at all. 


73
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W6EM
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Posts: 1925




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« Reply #37 on: August 15, 2013, 03:25:49 PM »

I found with my old 30-L1s that using the muffin fan to blow downwards, thus slightly pressurizing the cabinet, would cool it a bit better. 

But either direction is better than no fan at all. 


73
Now, that's amazing.  Ever heard of "the chimney effect?"  (Warm air tends to rise up all by itself).  So, sucking it up should be better than blowing it down, all things being equal.  Then again, it has probably got a lot to do with where the fan lies with respect to cabinet cover louvers, fan CFM rating, fan rotation speed, etc., etc.
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KE3WD
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« Reply #38 on: August 15, 2013, 04:41:45 PM »

Now, that's amazing.  Ever heard of "the chimney effect?"  (Warm air tends to rise up all by itself).  So, sucking it up should be better than blowing it down, all things being equal.  Then again, it has probably got a lot to do with where the fan lies with respect to cabinet cover louvers, fan CFM rating, fan rotation speed, etc., etc.

What's amazing is your attempt to correct an old design engineer who actually had to deal with the problem. 

That chimney effect presumes a passive cooling system. 

Once we move to powered air cooling, it is a simple fact that pressurized air inside an enclosure that has an exhaust in it somewhere can effect more cooling, due to the increased amount of air molecules that can come into contact with the hot body. 

And, stirred air can conduct more heat away from the hot body as well, for the same reason. 

Setting a muffin fan on top also subjects the fan itself to the heat flow, which can really decrease the Mean Time Before Failure of the fan. 

But thanks for playing.

and 73
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W0BTU
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« Reply #39 on: August 15, 2013, 06:31:22 PM »

There's an audiophool site selling hi-fi amps with water-cooled 833A triodes. Even though almost the entire tube is immersed in water, the plate dissipation does not increase nearly as much as you would think.

I've always believed that "if some airflow is good, then more is better, and a whole lot is just right". However, as long as there is a vacuum between the anode and the airflow (or waterflow) across the glass, the plate can still only dissipate so much heat via radiation.

That's why external anode tubes were invented, like the 4CX250B and 4CX1000A. In those tubes ---and water and vapor cooled tubes-- more air, etc. does translate into higher plate dissipation.
« Last Edit: August 15, 2013, 06:46:56 PM by W0BTU » Logged

W0BTU
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« Reply #40 on: August 15, 2013, 06:38:55 PM »

... the parts of the tube that get hot are inside a vacuum with very little to conduct the heat to the tube envelope where the air can cool it.  Making this problem worse is the fact that the wider axis of the plates face each other in the two tubes, so a good third of the IR radiation that comes off each tube goes straight into the neighbouring tube.  The rest of the IR radiation bounces around the nice shiny aluminum sides of the cage. The air blowing around the cage doesn't do anything to reduce any of that IR radiation until it stops reflecting and gets absorbed into something and is converted to real heat.  Until that point, the IR radiation is as likely to hit the tube plates as anything else.  Having that radiation absorb into /anything/ else is better than those plates.  If the temperature of that anything subsequently rises, then great!  Now the fan can actually cool something.

Almost anything should be better than having two radiatively cooled vacuum tubes sitting inside a shiny box where the only method of cooling is air blowing uselessly on the tube envelopes.  ...  At the very least, I intend to put a barrier between the two tubes to prevent their radiating into each other.  That alone will improve their cooling by a third.

I think I'll get a thermal imaging camera from work and make an experiment out of this.

Now HERE is a ham who understands the physics of heat transfer! Very well said!!

I was going to put a barrier between my parallel 833C triodes in my homebrew amp (probably an angled reflective one, but it might be dull black and hollow with air flowing through it). I haven't yet.

http://www.w0btu.com/833C_linear_amplifier.html

If you do those experiments, by all means post them here.

EDIT: Probably, increased airflow would help keep the glass from melting and 'sucking in', even if it doesn't help cool the plate all that much.
« Last Edit: August 15, 2013, 06:50:39 PM by W0BTU » Logged

W6EM
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Posts: 1925




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« Reply #41 on: August 15, 2013, 08:32:48 PM »

.....What's amazing is your attempt to correct an old design engineer who actually had to deal with the problem.

Design engineer?  Design engineers of the mechanical variety ususally don't get sent out to troubleshoot elevators with HTs in their tool boxes.  Technician seems to fit that example. 

Quote
......And, stirred air can conduct more heat away from the hot body as well, for the same reason.
  Ala forced air cooling.  Yes.  But, heated air is lighter and tends to rise.  Ask any HA balloonist. 

Quote
Setting a muffin fan on top also subjects the fan itself to the heat flow, which can really decrease the Mean Time Before Failure of the fan.
 I'll remember that if my range hood blower conks out.

Interesting about the IR radiation from the hot plates through the envelopes.  I guess there was someting to the old black-body tube shields besides the electrical benefits of same.

Also, as I recall, external anode tubes are usually forced-air cooled from the bottom, so perhaps there just might be a reason to inject ambient room air below the heat source to be cooled, eh?

 

 

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KE3WD
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« Reply #42 on: August 16, 2013, 10:04:09 AM »

Design engineer?  Design engineers of the mechanical variety ususally don't get sent out to troubleshoot elevators with HTs in their tool boxes.  Technician seems to fit that example. 

I wear both hats, having started out as a black kid who loved this hobby and turned it into a career by earning my 1st phone as a high school senior, then earning my way through BSEE by working hard as a repair technician.  The Masters came through stipends and such, predicated on a lot of hard work on my part, coupled with being able to repair the TVs, HiFi's and Ham Radios of those who were my profs but couldn't troubleshoot their way out of a simplest of testbench problems.  I worked for two decades in the university as research technologist, field robotics, nuclear cleanu[p robotics, space robotics, large scale construction machine robotics, autonomous vehicles, in all cases getting the heat out and away from electronics was and still is paramount to success. 

Quote
  Ala forced air cooling.  Yes.  But, heated air is lighter and tends to rise.  Ask any HA balloonist. 

Illogical argument.  WTF does a hot air balloon have to do with the use of forced air in cooling electronics? 

Quote
Interesting about the IR radiation from the hot plates through the envelopes.  I guess there was someting to the old black-body tube shields besides the electrical benefits of same.

Sorry, I cannot afford to suppose things.  My information comes from the empirical, thingw such as the use of manometers, thermocouples, dataloggers and the study of physics in order to solve these sorts of problems. 

If you are referring to the old metal-cased vacuum tubes brought out around the WWII era, the coating was black on them more likely due to available coatings than anything having to do with black body radiation.  Besides, those tubes were not high power transmitting tubes, most of them were signal power or rather low level beam tetrodes such as the 6L6, 6V6, etc. - and heat from those was not anywhere near the situation encountered with the RF output tubes. 

Still, pressurizing those environments, rather than attempting to evacuate the air, is a more efficient method of moving heat out of the enclosure.  That is simply because evacuation can often get us into the problems incurred due to decreased AMOUNT of available air that serves as the medium for transferring said heat. 

I don't really like using the term, "heat" - it is relegated to the 18th century thought that there was a separate entity known as heat.  We now have proven over and over again that it is energy that causes molecules to vibrate at faster speeds that raises the temperature, not some magic mystical "heat" - which really does not exist.  Ask a physicist about that. 

Quote
Also, as I recall, external anode tubes are usually forced-air cooled from the bottom, so perhaps there just might be a reason to inject ambient room air below the heat source to be cooled, eh?

You've introduced a variable in order to make an argument here. 

The conversation was never about external anode tubes until now.  The conversation is about glass envelope tubes. 

Still, the chimneys used for tubes such as the 4CX series, etc. are PRESURIZED and not evacuated, for the very same reasons as I have cited. 


73
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W6EM
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« Reply #43 on: August 16, 2013, 06:06:33 PM »

Quote
  Ala forced air cooling.  Yes.  But, heated air is lighter and tends to rise.  Ask any HA balloonist. 

Illogical argument.  WTF does a hot air balloon have to do with the use of forced air in cooling electronics?

Heated air is less dense, therefore lighter and tends to rise.  That would assist in the process of forcing cool air up and through heated fins and out an enclosure above. 

Quote
Quote
Interesting about the IR radiation from the hot plates through the envelopes.  I guess there was someting to the old black-body tube shields besides the electrical benefits of same.

Sorry, I cannot afford to suppose things.  My information comes from the empirical, thingw such as the use of manometers, thermocouples, dataloggers and the study of physics in order to solve these sorts of problems. 

 

If you are referring to the old metal-cased vacuum tubes brought out around the WWII era, the coating was black on them more likely due to available coatings than anything having to do with black body radiation.  Besides, those tubes were not high power transmitting tubes, most of them were signal power or rather low level beam tetrodes such as the 6L6, 6V6, etc. - and heat from those was not anywhere near the situation encountered with the RF output tubes.

No. I was referring to the shields of smaller tubes that were black with serrated fins surrounding them.[/quote] 
 
Quote
I don't really like using the term, "heat" - it is relegated to the 18th century thought that there was a separate entity known as heat.  We now have proven over and over again that it is energy that causes molecules to vibrate at faster speeds that raises the temperature, not some magic mystical "heat" - which really does not exist.  Ask a physicist about that.
 
You may not like it, but classical thermodynamics and heat transfer (via conduction, convection and radiation) are established areas of expertise.
Quote
Quote
Also, as I recall, external anode tubes are usually forced-air cooled from the bottom, so perhaps there just might be a reason to inject ambient room air below the heat source to be cooled, eh?

You've introduced a variable in order to make an argument here. 

The conversation was never about external anode tubes until now.  The conversation is about glass envelope tubes. 

Only to help show why its more desirable, even in a pressurized example, to inject cooler air below the heat source.
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QRP4U2
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Posts: 262




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« Reply #44 on: August 16, 2013, 11:31:02 PM »

Quote
I don't really like using the term, "heat" - it is relegated to the 18th century thought that there was a separate entity known as heat.  We now have proven over and over again that it is energy that causes molecules to vibrate at faster speeds that raises the temperature, not some magic mystical "heat" - which really does not exist.  Ask a physicist about that.  

Heat is not an archaic term.

Heat is the exchange of energy between two bodies at different temperatures, or Heat is the transfer of energy between a system and its environment because of temperature difference between them.

Hence, you have the terms, heat transfer or heat flow.

Quote
Still, pressurizing those environments, rather than attempting to evacuate the air, is a more efficient method of moving heat out of the enclosure.  That is simply because evacuation can often get us into the problems incurred due to decreased AMOUNT of available air that serves as the medium for transferring said heat.  

I agree. Blow cooler, denser air in and let the hot air evacuate via forced convection and forget about coating the tubes with paint.

Phil - AC0OB

« Last Edit: August 16, 2013, 11:47:05 PM by QRP4U2 » Logged

AC0OB - A Place Where Thermionic Emitters Rule!
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Besides, when you're a Ham, you experiment with and improve boat anchors - that's what you do!. Smiley
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