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Cooling a Pair of 4CX250B




 
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Author Topic: Cooling a Pair of 4CX250B  (Read 1252 times)
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W0PWE
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« on: March 18, 2020, 06:58:06 PM »

I am in the process of re-building an old amp that my dad built in the 70s. My goal is to use it at the 100 watt carrier level. It uses a pair of 4CXxxx tubes and I have both 4CX250B and 4CX350A tubes as options. The sockets, squirrel cage fan, 4CX250s and a few other parts came out of an old military VHF transmitter that is now long gone.

The grid compartment is roughly 5 wide, 11 long and 4 deep with the fan blowing air in the top rear and the tube sockets on top towards the front. Tube sockets look to be proprietary but probably not much different than the SK610 in terms of airflow design. Dad had made a shroud to contain the air coming up around the screen rings and help it to go through the anode fins. The fan is a 1/8 horsepower squirrel cage type with a wheel that is 2.5 diameter and 2.75 wide.
 
I dont feel that the tubes are getting enough cooling airflow. With just limited testing I softened the solder on the anode connectors. My anode connectors are homebrew from inch brass strip and similar to the those of the EJ Johnson 124-116 socket. With the tubes removed I can feel good air flow coming up through sockets but with tubes inserted, the tube base and screen ring severely limit the flow.
 
I made a test chamber with a cardboard box all sealed up, the blower, holes for a pair of tubes and a homebrew monometer. With a pair of tubes stuck in their holes air flow through the fins seems good. The monometer does not move though, even with the tube holes restricted or closed off completely.

My 1987 ARRL Handbook has a nice section on the subject. It shows some example blower data and the Dayton 4C440 looks like it would do the job (the 4CX350s need about 12CFM at 0.6 water. ) But that fan is roughly equivalent or maybe a little smaller than the one I have and mine wont even wiggle the monometer.
 
I would appreciate any suggestions on how to cool these tubes. It seems there are plenty of fans or blowers out there with the necessary specs but I get the feeling Im missing something obvious here. Thanks and 73.
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« Reply #1 on: March 18, 2020, 08:54:04 PM »

The pitch of the blades makes a big difference in airflow.  Especially when forcing air through the restrictive sockets and fins.

You need to make sure you have needed cfm with the rated backflow.

IE, double the necessary cfm of a single tube at the same cfm.

I don't remember the model number of the two tube 250B box I built is.  It's at home, and I'm in the parking lot at a store stocking up.

We go on lock down tomorrow, so I get to play antennas and radios!

--Shane
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« Reply #2 on: March 18, 2020, 10:34:09 PM »

Is the amplifier running efficiently? You should get about 60% peak efficiency if everything is in order. If efficiency is poor, the tubes will have to dissipate extra heat which requires extra cooling (or makes then run extra hot).

What is the input vs.output power when properly tuned?
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« Reply #3 on: March 19, 2020, 06:20:37 AM »

Remember, 4CX350's are class AB1 only. No grid current. For VHF FM or HF class C, stick with 250's. See the thread, "Need Some Help With My Amp Project" ST
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« Reply #4 on: March 19, 2020, 08:02:22 AM »

Let's see some pictures please?

Tubes in and out (need to see the sockets).

The "plumbing" needs to be correct.

From your description the air is blown down from the anode end?
Not up from a pressurized sub chassis that the tube sockets are
mounted in?

There needs to be a chimney if it is the second method.

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« Reply #5 on: March 19, 2020, 01:04:09 PM »

Thanks for the response and thanks for pointing me to the thread  "Need Some Help With My Amp Project. I read the whole thing and found some great info there. I will try to get some pictures of the sockets etc. but first let me provide a little more info.

It is a pressurized grid chamber so flow is up through the sockets and then through the anode fins. I do not have chimneys but I have ordered materials to make them.

I intend to run class AB1 and I have separate meters for both control grid and screen. I have built new power supplies and both the grid and screen supplies are regulated and have bleeders so that I can see negative current on the meters. The screen has a 12.5K bleeder to provide the roughly 15ma per tube as described in the Eimac data sheet.

After much fooling around with my NanoVNA I believe I have the Pi network output set up properly. The screen current peaks at resonance and dips with loading per Eimac newsletter AS13 Understanding Tetrode Screen Current by W6EMD.
 
Input circuit is a 100 ohm swamping resistor. With the 4CX350s I need to keep the drive below 4 watts or I see negative grid current and positive screen current. Low drive requirement is fine with me as I intend to eventually drive it with some type of homebrew low level exciter.

In AB1 my efficiency is about 50%. With 800 watts DC input the output is pretty close to 400W.

Things may not be as bad as I first thought. Last night I ran a test and monitored the anode temperature with an IR thermometer. Sitting with zero signal plate current (200ma) it took about 10 minutes for the temperature to stop climbing and it settled in at about 280F (138C). Keydown at 350 watts output for 2 minutes warmed them up to 330F (165C). I wasnt brave enough to run key down longer than 2 minutes but it looked like the temp was starting to stabilize.

I know I need to stay well away from the datasheet maximum of 250C but I dont know what kind of temperature I should expect under normal operating conditions. Again, my goal is to run 100 watts carrier 400W P-P.
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« Reply #6 on: March 19, 2020, 01:37:47 PM »

With an efficiency of 50% at 400W output you should see about 25% efficiency when the drive is reduced to yield 100W output. Figure on 300W of Pd with a dead carrier and 400W Pd at modulation peaks or about 350W Pd on average. Running it tuned to 350W output, as you have, is probably a good test as to how much it will heat up when in the full AM service you have planned.

Good luck with your dad's amp. Few of us get the chance to run a home brew hand-me-down.
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« Reply #7 on: March 19, 2020, 05:01:32 PM »

You can NOT run them without chimneys. The air won't pass through the fins with enough
velocity and flow.

Probably you can get away with some PVC pipe for testing only.

Teflon will work.
The originals were ceramic.
If you have a local ceramic making place, just make some out of pottery ceramic.
Actually you can make it by merely casting the right grade of gypsum.
It can be fired, or not.
Fired, you can glaze it.
Ought to work unfired.
Super strong stuff, stronger than concrete, btw.

The only critical dimension is the ID of the tube.
That ought to be easy enough to do with any number of formers... the outside
is non critical.

If you make a "dummy" chimney out of say plastic or wood - you can use the latex mold making
stuff from a hobby store to make the mold, and then just pour it... wait for it to dry.

Again, this stuff can be poured or gooped depending on the type.
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« Reply #8 on: March 19, 2020, 05:20:33 PM »

I am in the process of re-building an old amp that my dad built in the 70s. My goal is to use it at the 100 watt carrier level. It uses a pair of 4CXxxx tubes and I have both 4CX250B and 4CX350A tubes as options. The sockets, squirrel cage fan, 4CX250s and a few other parts came out of an old military VHF transmitter that is now long gone.

The grid compartment is roughly 5 wide, 11 long and 4 deep with the fan blowing air in the top rear and the tube sockets on top towards the front. Tube sockets look to be proprietary but probably not much different than the SK610 in terms of airflow design. Dad had made a shroud to contain the air coming up around the screen rings and help it to go through the anode fins. The fan is a 1/8 horsepower squirrel cage type with a wheel that is 2.5 diameter and 2.75 wide.
 
I dont feel that the tubes are getting enough cooling airflow. With just limited testing I softened the solder on the anode connectors. My anode connectors are homebrew from inch brass strip and similar to the those of the EJ Johnson 124-116 socket. With the tubes removed I can feel good air flow coming up through sockets but with tubes inserted, the tube base and screen ring severely limit the flow.
 
I made a test chamber with a cardboard box all sealed up, the blower, holes for a pair of tubes and a homebrew monometer. With a pair of tubes stuck in their holes air flow through the fins seems good. The monometer does not move though, even with the tube holes restricted or closed off completely.

My 1987 ARRL Handbook has a nice section on the subject. It shows some example blower data and the Dayton 4C440 looks like it would do the job (the 4CX350s need about 12CFM at 0.6 water. ) But that fan is roughly equivalent or maybe a little smaller than the one I have and mine wont even wiggle the monometer.
 
I would appreciate any suggestions on how to cool these tubes. It seems there are plenty of fans or blowers out there with the necessary specs but I get the feeling Im missing something obvious here. Thanks and 73.


According to tube specs you need about minimum of 8 cfm for two tubes. If you can fit a modern muffin fan to the chassis I think sufficient airflow will result.

Mechatronics has both DC and AC axial fans:

https://www.mechatronics.com/products/dc-axial-fans.php

https://www.mechatronics.com/products/ac-axial-fans.php

https://www.mechatronics.com/products/dc-high-airflow-fans/MR4020/


Phil

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« Reply #9 on: March 19, 2020, 06:01:43 PM »

I am in the process of re-building an old amp that my dad built in the 70s. My goal is to use it at the 100 watt carrier level. It uses a pair of 4CXxxx tubes and I have both 4CX250B and 4CX350A tubes as options. The sockets, squirrel cage fan, 4CX250s and a few other parts came out of an old military VHF transmitter that is now long gone.

The grid compartment is roughly 5 wide, 11 long and 4 deep with the fan blowing air in the top rear and the tube sockets on top towards the front. Tube sockets look to be proprietary but probably not much different than the SK610 in terms of airflow design. Dad had made a shroud to contain the air coming up around the screen rings and help it to go through the anode fins. The fan is a 1/8 horsepower squirrel cage type with a wheel that is 2.5 diameter and 2.75 wide.
 
I dont feel that the tubes are getting enough cooling airflow. With just limited testing I softened the solder on the anode connectors. My anode connectors are homebrew from inch brass strip and similar to the those of the EJ Johnson 124-116 socket. With the tubes removed I can feel good air flow coming up through sockets but with tubes inserted, the tube base and screen ring severely limit the flow.
 
I made a test chamber with a cardboard box all sealed up, the blower, holes for a pair of tubes and a homebrew monometer. With a pair of tubes stuck in their holes air flow through the fins seems good. The monometer does not move though, even with the tube holes restricted or closed off completely.

My 1987 ARRL Handbook has a nice section on the subject. It shows some example blower data and the Dayton 4C440 looks like it would do the job (the 4CX350s need about 12CFM at 0.6 water. ) But that fan is roughly equivalent or maybe a little smaller than the one I have and mine wont even wiggle the monometer.
 
I would appreciate any suggestions on how to cool these tubes. It seems there are plenty of fans or blowers out there with the necessary specs but I get the feeling Im missing something obvious here. Thanks and 73.


According to tube specs you need about minimum of 8 cfm for two tubes. If you can fit a modern muffin fan to the chassis I think sufficient airflow will result.

Mechatronics has both DC and AC axial fans:

https://www.mechatronics.com/products/dc-axial-fans.php

https://www.mechatronics.com/products/ac-axial-fans.php

https://www.mechatronics.com/products/dc-high-airflow-fans/MR4020/


Phil



Not sure about that.

CPI shows more airflow required.

Double the tubes, double the cfm.  Static pressure stays the same.  6 cfm is needed at 250 watts PDiss.

--Shane
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« Reply #10 on: March 19, 2020, 07:05:08 PM »

Thanks for the continued support and ideas. I never thought of making my own ceramic parts (chimneys) but I have a friend with a kiln so that is possible. Actually it sounds like fun. I have ordered some 0.010" Nomex paper and I will start with that but perhaps will do some testing with PVC as suggested.

It had a 4.25 inch muffin fan in it but I went back to the squirrel cage thinking it would work better with the relatively high static pressure. There are some high pressure muffin fans available now days. I think they were developed for pushing air through PC heatsinks. If I buy one I will remember the comment I read somewhere that said "your fan is too big if the tubes won't stay in their sockets" hi.

I think I figured out how to put pictures in the gallery and use attachments but it looks I can only attach 3 to the message. A few more are in the gallery.

Phil - It was great to meet you at the Perry RF Fest in Feb. Doesn't sound like we will be gathering at hamfests anytime in the near future.  Sad


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« Reply #11 on: March 19, 2020, 08:58:35 PM »


Not sure about that.

CPI shows more airflow required.

Double the tubes, double the cfm.  Static pressure stays the same.  6 cfm is needed at 250 watts PDiss.

--Shane
KD6VXI

RCA tube specs for the 4CX250B/7203 showed 3.8 cfm per tube X2 = 7.6 cfm or rounded up 8 cfm, which is why a 10 cfm fan or larger was suggested and links given to possible fans.

https://frank.pocnet.net/sheets/079/7/7203.pdf


Phil
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« Reply #12 on: March 19, 2020, 10:02:55 PM »

Imho, centrifugal blower is the only option for this application.

Muffin fans are not designed to work into a static air column.

The tubes should not be run without chimneys installed.
PVC will work for short tests, or as long as the operating temp at
the outer fins remains below the melting point of the PVC.

Take a look at the pix of the Eimac chimneys - they're tapered,
but there is no actual need for that. Note that they clip onto those
clips facing out on the socket assembly you have, and the brighter area
is where they formerly sat.

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« Reply #13 on: March 20, 2020, 12:03:23 AM »

OK, I'm a little slow but I'm beginning to understand. My first mistake was in thinking a chimney is a cylinder that takes the hot air exhausted from the tube and conveys it out of the enclosure - like a fireplace chimney. I have looked at pictures of the SK606 chimney many times but didn't really understand what they were made of or how they worked. To further confuse me I have a similar part that I thought was a SK606 but it not at all the same animal. After looking closely at SK606 pictures and info I understand and I can see why what I have won't work.

What I have is the box or shroud shown in the attached picture. So I believe that when the air comes up from below it expands into this large volume and looses the pressure it needs to blow through the fins at the correct velocity. My thermodynamics might not be completely accurate but this is clearly a different flow situation than that of the SK606 chimneys.

I found a drawing of the SK606 with dimensions. I can create a 3D model, print a dummy on my 3D printer and then make a mold and gypsum or ceramic parts as you described above. If I happen to have a piece of PVC or something of the right ID I will play with that first.


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« Reply #14 on: March 20, 2020, 12:04:10 AM »


Not sure about that.

CPI shows more airflow required.

Double the tubes, double the cfm.  Static pressure stays the same.  6 cfm is needed at 250 watts PDiss.

--Shane
KD6VXI

RCA tube specs for the 4CX250B/7203 showed 3.8 cfm per tube X2 = 7.6 cfm or rounded up 8 cfm, which is why a 10 cfm fan or larger was suggested and links given to possible fans.

https://frank.pocnet.net/sheets/079/7/7203.pdf


Phil

I believe I'd go with the higher flow rate., just to be safe.  As I stated, that was the Eimac spec downloaded from the Eimac website.

Having built enough 250b amps to fill a truck, I've found a lot higher airflow needed with both Eimac and Amperex  tubes.

That spec sheet is from 61.  This one is 74.

https://frank.pocnet.net/sheets/140/7/7203.pdf



To each his own, but I use a higher cfm blower with mine.

--Shane
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« Reply #15 on: March 20, 2020, 12:07:42 AM »

Why not just buy the correct chimneys instead of spending so much time building your own? They are plentiful on the market and can usually be had for $20 or so.
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« Reply #16 on: March 20, 2020, 12:38:09 AM »

There's one thing to know about running external anode tubes...   If they are small, like 4CX-250s, they tend to make a lot of air and fan noise before they get enough air to run cool as they should.   I had a TMC 4CX-350 amp with a pair and it sounded like a machine shop when put on the operating table next to me.  I ended up changing out to a larger blower with a Variac to slow it down. Even then, I needed to move it away to the other side of the room.

In contrast, a bigger tube like an 8877 (or larger) can use a bigger blower that is running slower rpm. The air does not make as much noise. The tube fins are wider spaced with less turbulence. I have a big amp that runs quieter than that old 4CX-350 TMC amp.

Do a mock-up first and see if you can live with the noise; especially paying attention to your on-air transmit S/N -  and mixing of the air noise with your audio.  A reasonably quiet shack is very important, especially for AM.

I think the loudest "small" rig I ever heard is a (R-392 /)  T195  ... good gawd!  (Collins design, single 4CX-150)

T
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« Reply #17 on: March 20, 2020, 03:20:58 PM »

One thing was said and it was not addressed. It was said that with the tube holes sealed off the manometer does not move. This is very important to look at.

Are you sure the manometer is built correctly? The free end must be open for it to indicate pressure by lifting a column of water x inches. The tubes anodes exhaust to open air therefore the manometer end is open to air. Sometimes the handbooks are not totally clear.

Even the simplest manometer will move for 0.6 inch of water.
What is the inside diameter of your manometer tubing?

Whether it is 12CFM (for a pair?) at 0.6" of pressure water column, or 6.4 CFM per tube at 0.82 inch of water column (pick one) the manometer will show it. As it was mentioned, more pressure = more flow = more cooling. Nothing wrong with more pressure except noise.

(I ran an NCL-2000 sitting on a "wind chest" I made from an old 12" bud rack, top door removed, with a big dual squirrel cage rackmount blower in it, and it was able to run for several hours at 100% output to power an experiment. When later shut off and discharged, the anodes and power transformer were cool to the touch. That's what extreme airflow gets you. I never bothered to measure the pressue on that.)

The truth is that once the tubes are in the sockets and there are chimneys in place sealing the anodes to the chassis, the manometer reading is all you need to know, provided the air exiting the tops of the anodes can escape freely. Eimac et al. have kindly given tables for this because it is easy to measure.

The reason for this is because the pressure is directly lost according to the airflow for that tube. You can make chimney temporarily from paper and electrical tape for the manometer/pressure test.

Here is a video of one I built in action.
http://bunkerofdoom.com/3cx3000/100_2086a.MOV

It shows just over 2&7/16" (2.4375") of water, half on each leg of the clear manometer tube, with one side moving down and the other up.

Does yours do this or not move? It should clearly be able to indicate 0.3" (5/16") on each side. No need to split hairs but there will be some movement. If not, there is something wrong.

More accuracy can be had by tilting the manometer. The column may move 4 or 5 inches horizontally but will still rise vertically only the distance proportional to the pressure. Dwyer makes those, and uses a quite thin tubing. Special thin fluid is used in them but note the expanded scale from 0-2". Where uptime is important you can make your own more compact one, use or make the thin fluid, and incorporate it into the front panel. OK that is way overkill but the topic deserved the info.


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« Reply #18 on: March 20, 2020, 04:45:50 PM »

...What I have is the box or shroud shown in the attached picture. So I believe that when the air comes up from below it expands into this large volume and looses the pressure it needs to blow through the fins at the correct velocity. My thermodynamics might not be completely accurate but this is clearly a different flow situation than that of the SK606 chimneys.

I found a drawing of the SK606 with dimensions. I can create a 3D model, print a dummy on my 3D printer and then make a mold and gypsum or ceramic parts as you described above. If I happen to have a piece of PVC or something of the right ID I will play with that first.

In terms of thermodynamics, most of the heat generated within the tube is conducted to the fins where cooling is to then take place via forced convection.

It appears from the picture that the airflow first cools the pins, as it should, and then blows up through fins. It also appears the chimney would further funnel the airflow in sort of a venturi effect toward the top, increasing air velocity slightly.


Phil  


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« Reply #19 on: March 20, 2020, 06:22:34 PM »

That "shroud" ought work just fine, as long as it is an air tight enclosure to the chassis and
around the sides.

You should feel a pretty good stream of air when the blower is powered up and no B+
on the tube... So if the plate current is within normal bounds, it ought to be fine.

The expansion of the air in the shroud ought not make any difference.
Of course the air input and the chassis also need to not leak.

This is the first time you showed a "shroud".

Imho, of course...

EDIT: A second look at the top of the shroud shows burning on the edges of the
top around the tube cutouts. Looks like it was green fiberglass pcb
material at one time. Very overheated. Which is why Eimac used ceramic. So, on a
second look, NG. The tube anode clamps can be modified and used, I expect. Unless the
sockets grab the anodes...


TMC PAL350 amp example below (same as the same amp using 4CX250B tubes)

That setup does not permit any "parasitic suppressors" on each tube... but you could
cut that in half... need be.

A non-contact laser thermometer from Harbor Freight will tell you the temp rise...


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« Reply #20 on: March 20, 2020, 08:29:39 PM »

if you don't like the noise of air cooling .... oil cooling is a very reasonable alternative if you figure out how to keep it sealed up ... afaik oil has a specific heat figure of hundreds of times better than air .... a gallon per minute is VERY generous at the kilowatt level
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« Reply #21 on: March 20, 2020, 10:38:28 PM »

I have rebuilt the manometer and it works a little better. The right side is inclined at about a 30 degree angle so I have a little better resolution. My tubing is 1/8 ID. Running a few of my fans in my closed off test box I can see a very slight movement in the water when I connect the manometer. Too small to measure even on the inclined side. The only thing that really moves it is my hot air gun. It shows about 2 of H2O pressure. Maybe I will disconnect the heating element and duct tape that thing into the amp (hi).
 
When connected to the grid chamber of my amp it also barely moves. That is with the squirrel cage fan. I will probably take the fan out again and try it in the closed test box but I imagine results will be less than stellar. Wish it would do as well as the one in your video. I guess I need a different fan although a ham friend of mine has the exact same fan in a 4CX250 VHF amp and he is having no problems.

I tried makeshift chimneys made of paper towel roll. Waving my hand over the tubes (with B+ off) I can now feel air coming out of the fins. There isnt much air moving but I was surprised to see that there was enough to blow out the flame on a stick match when I put it over the fins. With Idle current of 200ma the tubes still warmed right up to 300F in about 3 minutes. Thats as far as I wanted to go with cardboard chimneys.
 
You are right, that shroud or whatever we want to call it was made of green fiberglass PCB material and those brown spots are burns. That happened many years ago. I have not let it get anywhere near that hot. But those burns marks made me realize that I needed to pay attention to cooling when I got the thing running. I have parasitic suppressors and intended to install them when I made the anode connectors. But then I forgot. It will be easy enough to add them when (if) I wrap this thing up.


Nice to see the picture of the TMC PAL 350. I looked at a lot of amplifier designs before I started on this project but I did not run across the PAL 350 until you pointed me to Glenns post. That is a pretty impressive example of amplifier design.

Oil cooling is a neat idea and fun to think about but I think I have already gone too far with this old amp. Im beginning to believe it should have stayed in the garage attic where it has been for the last 25 years. Thank you all for the ideas and support.
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W0PWE
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« Reply #22 on: March 21, 2020, 06:39:50 PM »

Read this if you are bored. Long story short - I did some testing and I still need a bigger fan.  Wink

In my junk I found a CPU cooler with a Delta brand fan. The data sheet for this fan shows Max air flow (at zero pressure) of 68CFM and Max pressure (at zero airflow) of about 0.3 H2O.) This fan is inadequate for cooling my amp but at least it is a fan with known (or assumed) performance and I can use it to evaluate my test setup. So I mounted it on my test box, sealed up anything that might leak with duct tape, powered it up with maximum allowed voltage and checked the manometer. The inclined side moved maybe 1/16 but it is hard to say. Certainly not what I would expect with this fan. Manometers are pretty simple and its hard to mess one up. But it looks like I have succeeded. The tubing is used and there are stains inside from the water that was previously in it. Perhaps that impacts its ability to respond to these very low pressure changes. Normally I would run out to the home improvement center and get a fresh piece of tubing but Im voluntarily isolated so Im making do with what I have.

OK I cant test pressure so how about flow? I saw a guy on youtube testing a batch of CPU fans timing how long it takes to inflate a 30 gallon garbage bag. Hmmm, we could start a whole new thread on why that is an invalid test but lets try it. I fixed a 30 gallon bag to my test fixture and my CPU fan inflates it in roughly 10 seconds and by keeping all conditions as consistent as possible the results are pretty repeatable after 3 runs. Converting that number we get about 24CFM. Well, that seems like a ballpark number. At least its within the operating range of the fan. So then I removed the squirrel cage fan from the amp and tested it in the same way. It was about the same, maybe 9 seconds.

So then I made a collector out of cardboard that allows me to catch the anode exhaust air in the garbage bag. With the fan re-installed and cardboard chimneys taped in place it took 23 seconds to fill the bag. So that is about 10.5CFM. For a ballpark number thats believable.
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W4DNR
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« Reply #23 on: March 22, 2020, 12:04:53 PM »

In the 70s, I built an  80-20 amp in a Bud box similar to the Collins 30L-1 amp.
I used four Eimac sockets with the built-in screen bypass capacitors.
I stacked two 4 inch Rotron 100cfm  axial flow fans  ( for improved back pressure performance )
Under SSB conditions, the airflow temperature out of the top of the amp was acceptable.

A friend built a similar cooled PAIR of 4CX250b tubes and the amp ran hot with reduced airflow,
although he used the same two stacked Rotrons.

I'm sure his amp had more back pressure and stalled the Rotrons. 

This is where a large diameter slower rpm blower beats a smaller faster rpm blower.

Remote the blower in a wooden box and use a flex duct to the amp for lower noise.

Don W4DNR
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KK4YY
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Your best isn't as good as you can be.


« Reply #24 on: March 22, 2020, 01:48:34 PM »

One time I tried to remote a noisy blower to the outside of my house. Originally, the blower was mounted right behind a 4-400A with an Eimac air system socket. I extended the run with a hose of like size diameter. The hose was from a swimming pool filter. It was flexible due to the spiral shape of the hose.

When I turned it on I could hardly hear the blower outside the house. What I did hear was an amazingly loud howl caused by the spiral shape of the hose. It was louder than the blower had been and even more annoying. And all that turbulence and friction slowed the air output to a crawl. Cry

Maybe a hose with a smooth surface on its interior would have been better. Maybe a larger diameter hose would have been better. Maybe a shorter hose would be better. But maybe testing it out before I made a hole in the wall of my house would have been best. Wink
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