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THE AM BULLETIN BOARD => Technical Forum => Topic started by: K1JJ on March 16, 2005, 01:21:03 PM



Title: Question about Amplifier Tube Cooling
Post by: K1JJ on March 16, 2005, 01:21:03 PM
The 6M guys are axing good questions lately.  One of them is running a converted SB-220 [pair of glass 3-500Z's] doing 1300W out on 50 mc - not bad.

He axed about cooling. The SB-220 does not use chimneys, rather some fans blowing and sucking air. I told him that chimneys would be better for the tube seals, glass, etc.

But then he axed whether the plate structure inside the tube would run less red with better air flowing around the tube. At first I said "yes", but now I'm not sure.  I've realized that the plate structure is in a vacuum and does not know what the outside air is doing. It uses mostly heat radiation for cooling and the hot air outside gets swept away providing better outside glass/seal protection..

Any ideas on this?   Maybe it depends upon whether the tube is in an open area or is surrounded with a glass chimney. ie, if the air hangs around the tube getting hot with little air flow, does if re-radiate back into the plate structure causing it to get hotter/redder?  Or, maybe it's just a matter of degree - stagnant hot air will  result in less heat radiation transfer by blocking/buffering the heat vs: cool air? A thermal dynamics question I think.

I seem to remember that when running 4X1's with chimneys, whenever I increased the Variac for more blower air, the plate structure ran cooler [less red] but maybe  it was when I was in the Bizzaro Whirl where everything is backwards.  

T


Title: Question about Amplifier Tube Cooling
Post by: W2VW on March 16, 2005, 01:43:09 PM
Nice subject to generate interest Tom. Keep the red plates. They will eat any gas. It's the little metal thingys on the bottom which have to pass through the glass that are the worry. Double that for the SB220/221.


Title: Question about Amplifier Tube Cooling
Post by: W8ER on March 16, 2005, 04:00:04 PM
Tom,

I'm no expert on tube cooling but I stayed at a Holiday Inn Express last night.

The 3-500Z is cooled by radiation of the heat from the plate structure. Increasing the air flow around the tubes will help, obviously. There are two theories about cooling the 3-500Z tubes. That may be due partially because increasing the airflow around the tubes also removes heat from the metal parts of the enclosure immediately around the pubes also!

First is using a muffin fan, the way it was done in the Heath SB220/221. An article praising the cooling design by the Heath engineers said that not only did the method satisfy cooling around the plates of the pubes but the area of the chassis that was cut out beneath the chassis, and the proper orientations of the filament pins, allowed them to be properly cooled as well. This apparently was not an accident! My only comment here is that I have never heard of the solder melting and running out of the filament pins on a Heath SB220/221! Harbaugh Electronics offers an improved fan blade for that beast and if I had my old SB220, I's pop for one of those puppies.

Second, the old chimney and air socket combination. I'm not certain that this would be my choice, if I were designing one. Besides a problem with chimney design and a dearth of different shapes for 3-500Z chimneys, it don't seem to work da best. For instance my Henry 2K4 had a problem with the solder melting and running out of the filament pins. This can be unnerving in the middle of an old buzzard! The tubes were being run properly, within ratings but the indication was that the cooling wasn't working! If I remember properly, and that is tough with increasing age, the chimneys tops were slightly belled in and my belief is that that shape restricted air flow. Eimac chimneys, much more expensive, had fairly straight sides and the opening at the top was the same size as the opening at the bottom.

I did wish to point out that most "HAM" amps, that use 3-500Z's, use the Johnson "cheapie" ceramic sockets, lots of ceramic material with a few small hole to allow air to pass through. . Henry does .. Ameritron uses sockets made from glass baord (real cheapie)! The Eimac "air sockets" are very different and very expensive. they use an insulating ring and the contacts are fastened to the ring. The pins are open, sort of hanging in air. As I recall the Eimac sockets run upwards of $100 each! The use of "other" may account for the poor cooling that we have seen in the ham amps. Remember the full ratings are counting on proper cooling!

This picture was of a tube used in my Henry:

!(http://w8er.com/pics/3500pin.jpg)

In both cases, the painting of the surfaces that are immediately adjacent to the pubes with black non-reflective paint has been reported to help reduce the tube color.  High temperature black paint is readily available and maybe even powder coating might prove to be a great solution. If noting else, it sure looks pretty when you take a picture of the pubes in full color!

--Larry W8ER


Title: Question about Amplifier Tube Cooling
Post by: W1RKW on March 16, 2005, 04:04:26 PM
T,
I'm sure chimneys would be a definite benefit, max air flow around the tube is a must. You're dealing with heat transfer.  Because heat is energy heat will always move towards the cool zones. For example open the window of your house during this time of year, the cold doesn't come in but the heat goes out. Cold is the lack of energy or heat in this case.  One may not see a perceptible decrease in redness of the plates but I'm sure from the physics stand point the plates are somewhat cooler.  Even though the elements of the tube are in a so called vacuum there's no perfect vacuum better than space and yet heat is transferred from the sun to the earth in the form of visible and invisible light energy.

The glass of the tube and chimney do absorb heat but they also reflect some so removing the heat off the glass is a good thing with air flow much like a car engine. Even though your dealing with a less dense medium like air it still has heat transfer characteristics though they are not as efficient as a liquid.  

Painting any metal in close proximity to the tubes with flat black paint will eliminate or reduce infrared energy reflected back to the tube.  I had a tube audio amp that had a cage around the output tubes. I painted the cage flat black and the cage absorb more heat compared to when it wasn't painted.  So eliminating heat reflection and moving heat from the surface of the glass will help with heat transfer from the tube plate.


Title: Question about Amplifier Tube Cooling
Post by: W2VW on March 16, 2005, 05:53:34 PM
Quote from: W8ER

My only comment here is that I have never heard of the solder melting and running out of the filament pins on a Heath SB220/221!


You have now.


Title: Question about Amplifier Tube Cooling
Post by: W8ER on March 16, 2005, 06:44:45 PM
Quote from: Dave Calhoun W2APE
Quote from: W8ER

My only comment here is that I have never heard of the solder melting and running out of the filament pins on a Heath SB220/221!


You have now.


Interesting! Never have before Dave. Were you running it within spec .. meaning 300 or under and what kind of color were they showing?

--Larry


Title: Question about Amplifier Tube Cooling
Post by: W2VW on March 16, 2005, 07:06:48 PM
Not my amp. The guy said it was putting out 1500 Watts of slopbucket. 2500 Watts input verses the 2000 it was designed for. Another fella I know did the same thing. Those amps run a long time at design levels but most people beat the crap out of hammy amps.


Title: Question about Amplifier Tube Cooling
Post by: KA8WTK on March 16, 2005, 07:18:49 PM
Tom,
  I have been thinking about the 6m guy's question and I would think that you are correct in saying "Yes".

Just thinking about the physics involved, because I have no direct experience with tubes like that, leads me to the following thoughts:

1: The plates are going to radiate heat across the vaccum of the tube until it hits the glass.
2: The glass will absorb some of the heat and in turn radiate some.
3: Some of the heat will be reflected back to the plates by the glass.
4: Some of the heat will pass through the glass as raidient heat to be reflected back to the glass and plate by objects around the tube.

So, if you can keep the glass envelope cool, the glass will act like a heat sink for the plate making it run cooler. Painting the surrounding area black will absorb the heat that is radiated by the glass and dissipate it into the chassis. You are dealing with radiated and conducted heat. The radiated heat should act just like visible light and reflections seem to  come into play here.

There was mention made about the different styles of chimneys. Because the air is going to heat up as it passes the tube envelope, it makes sense that the top of the chimney should be "bigger" so the heated/expanded air can go out the top and not restrict flow.

In short, I agree with all the ideas presented in the thread so far and combining them all would lead to longer tube life for a tube that requires that much cooling. They all make good sense and I will keep them all in mind if I ever get or build a rig with a tube that requires a critical amount of cooling.

Good discussion, thanks!


Title: Question about Amplifier Tube Cooling
Post by: W8ER on March 16, 2005, 08:05:16 PM
Quote from: Dave Calhoun W2APE
Not my amp. The guy said it was putting out 1500 Watts of slopbucket. 2500 Watts input verses the 2000 it was designed for. Another fella I know did the same thing. Those amps run a long time at design levels but most people beat the crap out of hammy amps.


Oh!

A friend bought an old AL82 from me and swore that he was getting 3400 watts out of it. He did for about 2 weeks on the first set of 3-500Z's. I don't think he got as much out of the second pair!   :lol:

--Larry


Title: Question about Amplifier Tube Cooling
Post by: K1JJ on March 16, 2005, 08:59:37 PM
Thanks for the info, guys...

Bill/WTK-

Your info looks good and agrees with a conversation I had tonight on 75M with Stu/AB2EZ. He's a professor of elec engineering and quite sharp.  He agrees with you that the cooler the outside air is, the faster the heat transfer is from the internal plate structure - and the cooler the plate will be. For example, if the air is the same temp as the plate and not moving, then little or no heat transfer takes place. If it is 700 degrees cooler, then a large transfer occurs. There's more, but that's the main idea.


BTW, Larry, I had solder drip out of my 3-500Z's that had just a fan on them.  It was a Sigma XR-3000D.  Dino had the same thing happen.  I cut a 4" hole in the bottom of the cabinet and inserted a blower duct that pressurizes the bottom and the tube pins. This solved the problem.

I was able to repair the pins by QUICKLY heating the pins with a propane torch and soldering them back. Best to put on lots of heat quickly - not low heat for a long time or the glass/seals could blow out.

73,
Tom, K1JJ


Title: two years, still chicken to resolder, stupid amp
Post by: wa1knx on March 16, 2005, 11:24:21 PM
hi too voo,
      my sigma, sits on the shelf. i'd sicken if i broke two 3-500z
from solder melting - chicken - i might send the toobs out to you
to fix, and shipem back if you could help - - -
      so I'm stuck using a sb-200 - but working the wurld from
here!! btw, do you use silver solder or regular?

deano!


Title: Question about Amplifier Tube Cooling
Post by: Steve - WB3HUZ on March 16, 2005, 11:41:23 PM
It's no wonder the solder melted out. He was running the amp well in excess of its ratings. I don't think this incident is an indictment of the design used in the SB-220.

I don't think it matter whether a chimney is used or not. As long as enough air is moved across the pins and the envelope, everything will be OK. I don't think there is only one way to do this.

So, if the guy runs the converted SB-220 at the ratings of the original SB-220, I don't see why he would need to do anything further to it.

The 3-500Z is rated for full output to 110 MHz, so getting good numbers on 6 meters shouldn't be surprising.


I agree with Larry on the sockets. The Eimac air sockets are the best if your are going to use a pressurized subchassis and chimneys.

Heat flows (be it via radiation or conduction) from hot to cold. So the colder the air on the outside, the better/faster the heat flow from the tube.


3-500Zs getting a work out at HUZ Radio.
(http://www.amwindow.org/misc/glow.jpg)



Quote from: Dave Calhoun W2APE
Not my amp. The guy said it was putting out 1500 Watts of slopbucket. 2500 Watts input verses the 2000 it was designed for. Another fella I know did the same thing. Those amps run a long time at design levels but most people beat the crap out of hammy amps.


Title: Question about Amplifier Tube Cooling
Post by: W8ER on March 17, 2005, 12:20:02 AM
Just in case anybody was wondering about the socket types, I was able to quickly dig up these pictures and the prices of each.

This is the ceramic type that you will see in a lot of the amps like Henry's and other "better" manufacturers amps. Cost is $35 each:

(http://w8er.com/pics/cer3500.jpg)

Then there's the cheapie fiberglass socket. Used in the AL80B and the AL82 Ameritron amps at $22 each. Notice how little air each of these allows to flow around the seals of the tubes. Just little holes here and there:

(http://w8er.com/pics/fib3500.jpg)

And then there are the Eimac "AIR SOCKETS". These allow air to reach every part of the base of the tube. Notice that it is totally open. These could only be used in a closed chamber type of cooling system. The price of this socket is $79 however or nearly three times the cost of the others:

(http://w8er.com/pics/eim3500.jpg)

If you consider how much the more expensive "air socket" are and the price of the tubes, the air sockets may not be such a bad investment after all!

--Larry W8ER


Title: Question about Amplifier Tube Cooling
Post by: W3BYM on March 17, 2005, 07:45:40 AM
Hi Tom......Might as well put my two cents in the hopper.  I have had my SB-220 for 25 years and still using the same finals.  For the last 8 years it has been used on AM in the hi voltage (2700v SSB ) position. About a 200 watt resting carrier.  Oh the amp will do much more but you start to run out of head room cause of the PS.  At this point Pos Pks above 100% start falling.  Yes the plates glow a nice orange near their centers. The fan does a good job of blowing out all that hot air and keeps both the bottom and top seals cool enough...Obviously I've never had solder melting from the pins like them pricy amps.

73


Title: Question about Amplifier Tube Cooling
Post by: W8ER on March 17, 2005, 09:03:11 AM
Hey Tom ..

So that's why you're always so piss weak here in Ohio .. trying to keep them toobes cool!

--Larry ER


Title: Question about Amplifier Tube Cooling
Post by: W3BYM on March 17, 2005, 09:18:21 AM
At least I get out...BTW you better be carefull I know the "agent"

73


Title: Question about Amplifier Tube Cooling
Post by: W8ER on March 17, 2005, 09:26:08 AM
You best be careful .. I know "the Betty" and she likes me enough to make me cheesecake!

--ER


Title: Question about Amplifier Tube Cooling
Post by: WA1GFZ on March 17, 2005, 09:45:13 AM
The 3-500 does not have the same base as the 4-400. The old johnson sockets were made for the 4-125 through 4-400 base with the holes lined up with the tube base holes. This restricted the air flow requiring higher air pressure under the socket to move enough air through the small holes to cool the jug.
Eimac then built the 3-500 and 3-1000 tubes without this base to restrict
air flow so the tube could be cooled with a lower pressure under the socket because there was less restriction under the tube. The newer socket was open to allow more air flow.
A 3-500 in a 4-400 socket puts you back into needing more air pressure because the socket has the small air passages. One could drill holes around the socket to move more air over the glass.
SSB service may not be a problem but AM linear is making those
plates glow.
The heat on the plate travels up the stem to the plate cap. The higher the temperature of the seal the closer you are to failure. I had a stick on temperature sensor on the plate cap of my old 4-1000A rig that turned color if the radiator ever got too hot .
A red tube needs a lot of air past the radiator cap. Vertical fins would have been better. fc


Title: Question about Amplifier Tube Cooling
Post by: K1JJ on March 17, 2005, 10:47:50 AM
Yes, agreed, Frank.  It's standard procedure in all of my amplifiers to drill 1/2" chassis holes in a circle around the tube socket.  The glass chimney JUST covers them at the edge. Maybe 8-12 holes depending upon the size of the tube. This makes a huge difference in air flow through the chimney.
Works outstandng for 4-400's, 3-500Z's and especially well for 4X1's!

I even did this for my 6M external anode, ceramic tube 8877 HB amp. At first I had no holes and I went to a larger blower  - not much help, just raw restriction. Used an "official" 8877 air socket. After drilling the holes I needed a Variac to throttle down the air flow!  It passes so much air now it's like a hurricane and cool. Air still passes thru the tube fins but gets the additional flow of air on the edge. The blower works better cuz of less turbulance.  The best part about this is that the blower room noise of air is quieter because of less turbulance too. It consists of of mostly white noise rather than rumbling and whistling.

The ultimate cooling system is what I described above PLUS mount a BIG blower outside the wall (or outside the house) with a duct connected to the rig in normal fashion. Connect the duct to the blower so it SUCKS air out. The air comes in thru the TOP of the tube and down. VERY quiet with no turbulance or hiss. In addition, the whine of the blower is gone and the room stays cool in the warmer months. Reverse the connection outside and you can push air in and warm the room. But I found moisture from outside a problem to rusting parts, so I just suck air out now.  This is the best cooling system I've ever used for big tubes.  I can run QRO on AM in 90 degree WX and not even know the big rig is on.

Warning:  Do not use plastic dryer duct, etc for sucking air out - it will melt or deform. And do not use a solid material like PVC pipe, as it will act like a trumpet and conduct the blower noise into the room rather loudly. Rather, use a fiberglass reinforced flexible hose (4" diameter) that will withstand 350 degrees F . Available from McMaster on the web by the foot.

73,
Tom, K1JJ


Title: Question about Amplifier Tube Cooling
Post by: WA1GFZ on March 17, 2005, 11:38:14 AM
I just reran the dryer hose because the plastic crap traps lint and clogs the hose. Home depot sells the aluminum 4 inch cheap. I stick a sheet metal screw at each joint. You have to be careful with holes around the tube. You want enough air to flow across the pins. It is best to make a U tube and measure the pressure as you add bypass holes to verify the chassis pressure is still high enough. I did the same thing with the old 4-1000A rig.


Title: Question about Amplifier Tube Cooling
Post by: K1JJ on March 17, 2005, 12:15:34 PM
Quote from: WA1GFZ
I just reran the dryer hose because the plastic crap traps lint and clogs the hose. Home depot sells the aluminum 4 inch cheap. I stick a sheet metal screw at each joint. You have to be careful with holes around the tube. You want enough air to flow across the pins. It is best to make a U tube and measure the pressure as you add bypass holes to verify the chassis pressure is still high enough. I did the same thing with the old 4-1000A rig.


If you do a remote blower mount, the aluminum 4" will also "trumpet" and amplify the motor sound back to the rig. You need a fabric of some kind like fiberglass, etc. that will withstand some heat and is a poor conductor of sound.

As for the holes, you will find that usually enuff air finds it's way by the pins even with the extra holes. The path is very broad in the journey from the blower to the socket/pins. In fact, I usually use a sealed/pressurized  sub-chassis so that the tube compartment is maybe 6"X6"X6"  and becomes very efficient for air flow. I usually keep the bi-filar choke in there too so that it gets cooled.

T


Title: Question about Amplifier Tube Cooling
Post by: WA1GFZ on March 17, 2005, 12:23:52 PM
Hey Tom,
I see botox didn't work for you.


Title: Question about Amplifier Tube Cooling
Post by: K1JJ on March 17, 2005, 12:48:36 PM
Quote from: WA1GFZ
Hey Tom,
I see botox didn't work for you.


ih knarF,

thaW si a xotob??

[Bizzaro World message]

T


Title: Question about Amplifier Tube Cooling
Post by: Steve - WB3HUZ on March 21, 2005, 09:18:01 PM
Been doing some reading on this. Seems the amount of air flow over and away from (through the air system) the tube the important thing. You can determine the amount of power dissipated from the following.

Pd = 169Qa[T2/T1 -1],

where Pd is power dissipated,
Qa is air flow in CFM
T1 is air system inlet air temperature (K)
T2 is air system exhaust air temperature (K)

As you can see, the more air flow through the air system (Qa) the greater the potential power power dissipation.

You can get an idea of how much power your tube is dissipating by measuring the inlet and exhaust air temperatures. Let's use a 3-500Z as an example. The tube requires 13 CFM for proper cooling. If the inlet air was at room temperature, what would the exhaust air temperature be if the 3-500Z was dissipating 500 watts?

Rearranging the above formula to solve for T2 we get the following.

T2 = T1(Pd/169Qa +1)

Plugging in the numbers yields:

T2 = 294 [(500/(169 * 13)) + 1]        {70 degrees F equals 294 K}

T2 = 294 (500/2197 +1)

T2 = 294(0.228 +1)

T2 = 294(1.228 +)

T2 = 360.9 degrees K = 189.9 degrees F

That's getting pretty warm. Actually the exhaust air would be a little hotter than that because we didn't account for the power dissipated by the filament.

It's interesting to note that if we increase the air flow, the exhaust temperature decreases (e.g. for 20 CFM the temperature is 147.8 degrees F).

Has anyone here done any temperature measurements? If so, do they compare with these calculations? I have a 3-500 amp. I think I'll get a thermometer and see what's happening.

I also thought about the trick of drilling holes in the chassis around the tube to increase air flow. Check my thinking here, but if you are using a blower that can supply the required CFM AND handle the back pressure, I don't see how drilling holes helps. Given the proper blower, ALL the air  must pass through the socket and over the tube. It seems drilling holes just bypasses some of the air that would normally pass through the socket and over the seals on the pins.

Am I smoking dope here or what?


Title: Question about Amplifier Tube Cooling
Post by: K1JJ on March 22, 2005, 12:06:40 AM
Good info, OM.  Nice to see it reduced to a formula.

So back to the original question - from what you've read, do you feel that the plate structure in the vacuum glows less brightly when more air is passed by the outside glass envelope?  I think so myself...

As for the holes around the socket... After they are drilled I've seen perhaps three times the air flow passing thru the tube's chimney. I think it's either a matter that my cheap  blowers do not work well with back pressure, or perhaps the turbulance generated by the difficult path thru the socket causes flow problems.

I also think that just a small amount of air is needed by the seals at the bottom, and the majority is needed by the glass envelope up on top where the plate structure resides.  Whether or not the holes are there the pins get enuff air. So, I think any way to increase the overall flow thru the chimney past the plate is good.  Well, at least I've found with my latest 8877 6M linear that the air temperature is now luke warm, where before it was hot for the same blower/variac setting - perhaps triple the air flow now coming out of the tube's fins.

I realize that if Eimac wanted it run that way they wud have recommended it, but never mentioned it.  But it has worked for me with 4X1's, 4-400's, 3-500Z's  too. The Tron is who turned me on to it years ago. [The Guru Trogladite can't be wrong!  caw mawn -   :lol: ]

T


Title: Question about Amplifier Tube Cooling
Post by: W8ER on March 22, 2005, 12:35:40 AM
Guys, I ran across this great article on some cooling modifications made to a Hanry 5K and was unable to find it until a few minutes ago. In light of the discussion, I thought it might be interesting reading. Some of the techniques for both measuring the airflow and curing the "problem" was way over just interesting.

Cooling Mods for a Henry 5K (http://www.bctonline.com/~skelly/henry_amplifier/henry_5k_blower.htm)

--Larry W8ER


Title: Question about Amplifier Tube Cooling
Post by: Rob K2CU on March 22, 2005, 07:32:35 AM
A neat item to get to monitor your air temp is a low cost, dual display, indoor/outdoor digital thermometer.  Just for fun I used one to compare twmperatures at the top of my T4X-C with and without the little PC processor cooling fan that sits on top of the output tubes. Without fan, the air rose to 114 degrees F in a room with 68 degree air. ...and that was in standby.  with fan turned on, the temp dropped to 74 degrees.  OBviously, more testing is in oreder, such as comparing top mounted exhaust vs. rear mounted fan and blowing vs. sucking.


Another idea for comparing the color of the plate glow might be to build up an IR measuring circuit using a black plastic encapulated IR photo diode/transistor.  it could be mounted to look at the tube plate through the glass.  If cooling the plate stem actually takes heat out of the anode, then a drop in IR output should be measurable.  Multiple detectors could compare tubes.  This could also be used to verify if paiinting the inner walls of the Rf cage actually reduces back IR radiation heating of the plate.
It wouldn't give you any calibrated measurement, but would be good for comparisons.


Title: Question about Amplifier Tube Cooling
Post by: W2VW on March 22, 2005, 08:44:42 AM
Quote from: K1JJ


So back to the original question - from what you've read, do you feel that the plate structure in the vacuum glows less brightly when more air is passed by the outside glass envelope?  

T


Only is the inlet air is cooler than the outlet air....


Title: Question about Amplifier Tube Cooling
Post by: Steve - WB3HUZ on March 23, 2005, 10:13:30 PM
This is purely speculation on my part, but I think there is a point at which increasing the air flow across a tube will not improve the dissipation or more effectively cool the tube. My reason is that for a given inlet air temperature, there is a finite limit at which the heat can be radiated by the plate, transferred across the vacuum to the glass and then reradiated by the glass into the air steam. Once the air flow pulls away all the heat the plate/vacuum/glass system can provide, the cooling limit is reached.

Once again, this is just speculation and "thinking out loud" on my part. But, if my speculation is basically correct, and the tube manufacturers knew this limit, their CFM requirements for a given tube would hopefully reflect it (probably be somewhere reasonably close to the limit). So, the question becomes, in the case of a 3-500Z, is the 13 CFM air flow specification at the "cooling limit" number I speculated above? I don't know. But, if it were, then passing more air across the tube would not change the color of the glowing plate.

How's that for some BS?


Title: Question about Amplifier Tube Cooling
Post by: W2VW on March 23, 2005, 10:43:31 PM
Let the freakin' anode glow red. It was designed to work that way. Keep the bulb seals cool and you are set. If the anode is turning white due to over dissipation then you can blow all the cool air in Hoboken on it and still not help cathode bombardment.


Title: Question about Amplifier Tube Cooling
Post by: K1JJ on March 23, 2005, 10:46:43 PM
Quote from: Steve - WB3HUZ
This is purely speculation on my part, but I think there is a point at which increasing the air flow across a tube will not improve the dissipation or more effectively cool the tube.



Yes, it is probably a point of diminishing returns when the flow is big. But the air flow must get to the optimum point first. I found that when running the normal recommended air socket on an 8877 or 4X1, I had a very difficult time getting enuff air thru it to adequately cool the plate structure when piss beating the tube.... :lol:  

With my 8877 I put on a huge blower and it still seemed restricted/turbulent, the air flow was noisy and the air was hot. After drilling the holes the air cooled down noticably and was quieter.  So the bottom line is I had not reached the critical air flow in these examples and the holes helped to get there...  Again, I think the pins/seals need very little air being below the major heat source and the plate is where increased air helps. This indirectly keeps the pins cooler too by pulling would be plate conduction heat away from them.

This can all be solved by building a class E rig or picking up an SB-230 with a conduction cooled final, caw mawn.

T


Title: Question about Amplifier Tube Cooling
Post by: w3jn on March 24, 2005, 06:56:28 AM
The SB-230, however, is one amp you *don't* wanna piss-beat.  The 8873 toobs are rare and pricey, and don't take well to a good beatin'.

You fergot the other option - go with a sand-state leenyar.  'S what I've done... but I must say it is NOT silent due to xformer lamination hum.  Also after a long old buzzard the fans will suddenly come on, sounding like a B-29 spooling up for takeoff.  Fortunately, that's a rare occurrence, but it's enough to startle a guy.

73 John


Title: Question about Amplifier Tube Cooling
Post by: WA1GFZ on March 24, 2005, 08:18:23 AM
The cooler the air passing over the tube the more you can dissipate
up to the point where the plate melts. Heat travels to cold and wants to go up since heat contains upsadasium.  Remember the old days when guys
would mount a 6L6 upside down in a pan of water.
I bet you could really push a tube to the limit of emission if you keep it cool. Look at the pulse ratings of a tube. Heck the pair of 6DQ5s in my viking 2 have been switching a half amp peak at 1550 V since 1983 and show no signs of wear.  A plate can run Red as long as the glass doesn't melt. Yellow or white may be a concern.


Title: Question about Amplifier Tube Cooling
Post by: KL7OF on March 24, 2005, 09:36:05 AM
If you are into chimney cooling...Go to the sporting goods store and get a pyrex glass for a coleman lantern....They come in many sizes and cost less than 10 bucks ......


Title: Question about Amplifier Tube Cooling
Post by: K1JJ on March 24, 2005, 11:16:32 AM
Quote from: w3jn
The SB-230, however, is one amp you *don't* wanna piss-beat.  The 8873 toobs are rare and pricey, and don't take well to a good beatin'.

You fergot the other option - go with a sand-state leenyar.  73 John


Yep, the SB-230 is a popular amplifier lately for the local group on 6M...  One guy has converted his over to a mono-bander and is doing two more. Yes, the tube is hard to find, though they are buying the amps intact for reasonable prices right now.  They put out 600W silently on 6M when set up right.  And you don't wanna drill and inhale the tube's berlium? insulation. These days I doubt Heath wud take that risk with ham kit guys..

Yes, a solid state linear is a great way to go too. Price can range all the way up to the Icom PW-1 ?  that costs upwards of $7-10K+ ?...  Or luck out and get a surplus unit ot build one.   Push the botton on your new ricebox, it changes the antenna AND changes the linear's band. Call CQ on each band 160-6M every 2 seconds until your finger gets tired, caw mawn.

Then again, it's easier to get on the cell fone or internet, but many of us like to row around town with our vacuum variables or bread slicers.

T


Title: Question about Amplifier Tube Cooling
Post by: Art on March 24, 2005, 11:24:01 AM
the GI1b russian triode is a good substitute for the 8873 in the sb-230. . .yes, you will need to pressurize the cabinet with a muffin fan but it is a nice conversion. . . 'bout 500W out with 30W drive . . . the tube is about $20 on epay. . .


Title: Question about Amplifier Tube Cooling
Post by: W1RKW on March 24, 2005, 01:39:22 PM
Something I've always thought about doing with my car was to insert a couple of those solidstate peltier junction thermal cooling devices into my intake of the engine and reduce the intake temp during the summer and squeezing more hp out of the engine.  I've always noticed the cars performance changes when it's hot out but always ran best in the 70 degree range or lower.

One could do something similar to this and reduce the ambient temp by 10's of degrees and blow that cool air over a tube.  I'm sure a drop in ambient temp across the envelope would make a significant difference in performance compared to normal room temp especially during the warm months of the year.  

http://www.allelectronics.com/cgi-bin/category.cgi?category=450&item=PJT-4&type=store


Title: Question about Amplifier Tube Cooling
Post by: WA1GFZ on March 24, 2005, 03:34:40 PM
Yea that sounds great but you might need 100 amps at 12 volts to generate enough cold air to make a difference.  They are cool parts but power hogs.


Title: Question about Amplifier Tube Cooling
Post by: K1JJ on March 24, 2005, 04:02:02 PM
Yep, agreed.

I used one to cool my homebrew CCD camera for astronomy photo use.  It took some time to cool down to -20F, and  the current was about 30A at 13.8V.   The area it cooled was maybe a coupla square inches of aluminum slab-bacon that the tiny CCD chip mounted on.. [cold= low thermal chip noise]   I ran antifreeze thru the aluminum/Peltier to pull the heat away. The tank was about 20 gallons and warmed up at the end of the night from the Peltier "cold finger" heat transfer.  Not a very efficient system, but at that small scale it was FB for the job.

T


Title: Question about Amplifier Tube Cooling
Post by: W1RKW on March 24, 2005, 04:04:34 PM
maybe pumping cold air from an AC unit would be more efficient for tube cooling...


Title: Question about Amplifier Tube Cooling
Post by: WA1GFZ on March 24, 2005, 04:07:59 PM
How do you plan to turn the compressor?


Title: Question about Amplifier Tube Cooling
Post by: W1RKW on March 24, 2005, 04:10:20 PM
20Amps at 13.8Vdc for a 100watt pep slopbucket signal. Yep that's not to effiencient either but what the heck.   I guess BTU's is the issue here.  An AC unit probably would be best for tube cooling.  Modify a deep freeze unit to cool the tube if you're gonna use external duct work. Modify it with the plumbing then fill it up with some thermal mass and you get yourself the best tube cooling unit around.


Title: Question about Amplifier Tube Cooling
Post by: WA1GFZ on March 24, 2005, 04:16:45 PM
1KW of heat is a bit over 3000 BTU if I remember


Title: Question about Amplifier Tube Cooling
Post by: Steve - WB3HUZ on March 26, 2005, 11:42:52 AM
Looking at the Eimac data sheet, it appears moving more air over the 3-500s would not change the color of the plates because the air flow is solely for cooling the base and plate cap seals. (See the highlighted section below)

Quote

COOLING - Forced-air cooling is required to maintain the base seals at a temperature below 200º C, and the plate seal at a temperature below 225º C. Air flow requirements to maintain the above maximum temperatures are tabulated below. (For operation below 30MHz)

Code:

Base to Anode Air Flow

Anode                         Air Flow                     Pressure
Dissipation                    (CFM)                         Drop
(Watts)                                                     (in-H2O)

300                             6.6                         0.023
400                            10.3                         0.052
500                            13.0                         0.082


The anode of the 3-500Z operates at a visibly red color at its maximum rated dissipation of 500 watts.

In all cases, air flow in excess of the minimum requirements will prolong tube like. NOTE: Two 3-500Z tubes in a single amplifier, chassis mounted, may be adequately cooled by use of a fan so mounted as to pressurize the space below the sockets. Fans suitable for use ...... <cut>

In all cases, the only criteria of proper cooling is the temperature of the tube seals. (Emphasis added) Tube temperatures may be measured with the aid of temperature sensitive paint, spray , or crayon.



Your friend with the modified SB-220 may want to up the air flow, since the specifications given above are for 30 MHz and below.


Title: Question about Amplifier Tube Cooling
Post by: Steve - WB3HUZ on March 26, 2005, 11:55:36 AM
Quote from: WA1GFZ
1KW of heat is a bit over 3000 BTU if I remember


I don't think there is a direct conversion because BTUs are a units of energy and Watts are energy per time (joule per second). So, one BTU is equal to one kilowatt-hour.


Title: Question about Amplifier Tube Cooling
Post by: WA1GFZ on March 26, 2005, 06:05:44 PM
We looked it up at work when I was wondering how much KWH it would take to match the heat of my 20,000 BTU kerosene heater. I saw the number wiritten on the wall yesterday so I wouldn't forget.
It is a bit over 3400 BTU for 1 KWH so I would need about 6 KW of base board to match the heater.


Title: Question about Amplifier Tube Cooling
Post by: Steve - WB3HUZ on March 26, 2005, 06:49:42 PM
Yep, 1 kW is 3415 BTU/h


Title: Question about Amplifier Tube Cooling
Post by: W8ER on March 26, 2005, 06:55:53 PM
Quote from: Steve - WB3HUZ
Yep, 1 kW is 3415 BTU/h Give a man a fire and he'll be warm for a day; set him on fire and he'll be warm the rest of his life.


Steve, you seem to have a thing for heat!

 :evil:


--Larry


Title: Question about Amplifier Tube Cooling
Post by: VA3ES - Piss-Weak Ed on March 26, 2005, 07:12:23 PM
Quote from: W8ER
 Steve, you seem to have a thing for heat!

Yeah.... especially "cash heat" :badgrin:  :p .


Title: Question about Amplifier Tube Cooling
Post by: K1JJ on March 26, 2005, 07:30:30 PM
Interesting summary on the 3-500Z cooling, Steve.

According to a Google search, "Soft solder melts at 200 - 250 C and consists of tin and lead in varying proportions, with sometimes a trace of antimony. "

Some hits said about 180C - 200C.  

So looks like when the filament pin solder melts, the critical 250 C  degrees maximum is about to be reached on the seals according to the information.  So, a good thing it melted and shut down the tube.

Well, it looks like the majority thought [including me] that the color of the tube gets less bright with more air flowing. Now the Eimac info seems to infer that it has no effect on the plate color.  If so, the plate structure must rely solely on radiation cooling.

So it's back to my original first comment that the plate [in the vacuum] does not know what the outside air is doing.

However, with an external anus tube, air cools both the seals and plate structure.

This is what makes a good topic for discussion - we all learn something new.

T


Title: Question about Amplifier Tube Cooling
Post by: Steve - WB3HUZ on March 26, 2005, 11:10:44 PM
The effects of extended exposure to RF.

Quote from: W8ER
Quote from: Steve - WB3HUZ
Yep, 1 kW is 3415 BTU/h Give a man a fire and he'll be warm for a day; set him on fire and he'll be warm the rest of his life.


Steve, you seem to have a thing for heat!

 :evil:


--Larry


Title: Question about Amplifier Tube Cooling
Post by: Jack-KA3ZLR- on March 27, 2005, 05:42:55 AM
One of the many subsequent reasons I Like 813's, that Big Current Hogging piece of glass may Look good but, but the relative difficulties in handling, Cooling and feeding makes it not one of my favorites...

They will warm a Room thou.... :D


Title: Question about Amplifier Tube Cooling
Post by: WA1GFZ on March 28, 2005, 08:24:05 AM
Speaking of cash heat oil cost me $2.16 a friggen gallon last week.
New QTH R66.5 above and R31 in the walls.


Title: Question about Amplifier Tube Cooling
Post by: WD8BIL on March 28, 2005, 08:35:15 AM
Quote
If so, the plate structure must rely solely on radiation cooling.


You're probably right here Vu. .... for the most part!
I would think the seal and pin temps are also noticably affected by
heat conducted to them from the elements by those little wires !!!!
Particularly the plate and filaments.
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