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Cooling a Pair of 4CX250B




 
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Author Topic: Cooling a Pair of 4CX250B  (Read 1251 times)
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KD6VXI
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« Reply #25 on: March 22, 2020, 02:09:32 PM »

Everyone likes to use spiral flex because it's easy to use.

The turbulence it creates about halves the airflow and puts a beating on the blower.

If you can use non-spiraled (is that a thing???) then it's a lot better.

The 250B is a hard beast to cool, as the anode is so small and the fin spacing is minute. 

When I'm out in the shop today, I'll pull the blower model number off the 2 x 250 box I'm getting ready to ship out.

--Shane
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« Reply #26 on: March 22, 2020, 02:24:00 PM »

Shane:

You are absolutely right about spiraled, clothes dryer, plastic hose.  I learned the hard way and mention it sometimes. In addition to backpressure increases, turbulance adds additional air noise.

Look on the web for fiberglass, flexible ducting.  It is smooth inside and strong. The spiral is on the outside where it belongs. No turbulance here.


Also, for runs longer than 6", stay away from metal or PVC ducting. It makes a blower sound like an amplified trumpet. You want accoustical deadening material only.

T

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« Reply #27 on: March 22, 2020, 02:26:19 PM »

I did some testing and I still need a bigger fan.  Wink

So I'm both curious and bored...

Maybe something like this
https://www.digikey.com/product-detail/en/mechatronics-fan-group/UF190APA12-H1C2F/1570-1184-ND/5209881

data sheet page attached.

Note that sound drops 3db for 200 rpm (50 vs 60 Hz rating). You can probably slow it down with a variac or traic dimmer or whatever and get the sound lower.  This model has a flange. Many of the other similar ones on Digikey or Mouser do not, which makes mounting them a project in itself.  You could mount this in a box with a hose and put it outside the room, too.

Like Shane said, spiral tubing is horrible for airflow.  If you can mount it remotely, in a fixed relation to the amp, you can use ordinary PVC drain pipe -- smooth low loss interior -- or at least for most of the run.

Good luck and don't give up.

Ed


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« Reply #28 on: March 22, 2020, 03:30:28 PM »

OK.

Went out to the shop and completely disassembled the covers...

The blower on the pair of 250s is....

Sony SSF22C.

It's a 38CFM 10 volt blower.  It's running on a 14 volt power supply in this amp, and has run for a few years.

So it's outputting quite a bit MORE cfm in this application, but unless your blowing the tube out of the socket, you need more CFM.

Incidentally, this amplifier only runs in AM service.  It runs 2.5kv on the plates and output capability is well over a kw pep....  So tubes are run hard by the owner.

Original pair of tubes in it.  It came into my shop to have a switchable transformer or swamped grid input (so 10 or 100 Watt pep in) and variable regulated g1 and g2 supplies.

be prepared, it's not cheap.  I found it for a whopping 6 bucks!

https://www.surpluscenter.com/Electrical/Blowers-Fans/DC-Centrifugal-Blowers/38-CFM-10-Volt-DC-Sony-Blower-16-1505.axd

--Shane
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**edited to include a url and price.


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« Reply #29 on: March 22, 2020, 06:17:48 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 1/8Ē 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 2Ē of H2O pressure. Maybe I will disconnect the heating element and duct tape that thing into the amp (hi).
 

1/8" seems small for a water manometer. Due to capillary action and surface tension and being dirty, it could be erratic at low pressures, but it is moving and maybe it's just the diameter. The tubing should be at least 1/4" and clean too. Mine's dirty as you can see for I let the old water evaporate from it, instead of draining it.

Someone told me that a tiny amount of detergent breaks the surface tension, not sure if it's worth a try.

Fans. some people use them. Blowers are much better at overcoming twists and turns and weird restrictions.

My manometer and video - this was a larger blower removed from a transmitter that used a 4CX5000 and a 4-1000. I am going to use it for a 3CX3000 amplifier. I like a little overkill.
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« Reply #30 on: March 22, 2020, 07:08:28 PM »

Wow there is a bunch of good news here since I last checked! Thanks for all the input.

When scrounging around this morning I found a nice new piece of 3/8Ē I.D. tubing. I built a new manometer with it and it works great. Easy to fill, easy to read, and now I believe it. So you were correct to question the hose size Patrick Ė thanks. In my amp Iím still only seeing a lousy 1/8Ē of pressure but at least I have a way to measure it.
 
Don Ė I had some fun with your suggestion of stacking two axial fans. I never would have thought of that even though I actually had two of them on my bench sitting one on top of the other. These fans rotate in opposite directions and I think that is desirable. I tried them out with my new manometer and test chamber and they produce about ĹĒ of pressure at zero flow. Thatís the best fan I have so far and Iím going to install it in the amp to see what it does for me.
 
But I wonít need to install it permanently because Shane has the solution for me. Gosh Shane that was very nice of you to go out to the shop and tear into that amp to get the info for me. And you found a supplier with an awesome price! I really appreciate that. I have been fan/blower shopping on-line the last few hours and getting depressed. That Sony blower looks like one I saw in a commercial amp and if it works in the beast you have there it ought to cool my little amp just fine. Awesome!

Follow up on some earlier discussions about chimneyís etc. A ham friend has a pair of Eimac sockets and SK606 chimneys that he is going to send me in a few days. If the chimneys donít work with my sockets I will swap them out the Eimacs. Or I might just swap them anyway.
Thanks again for all the support.  73-Jerry
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« Reply #31 on: March 22, 2020, 07:16:24 PM »

You're welcome bud.

Should be more than enough to cool an amp that is run at sane levels.

Patrick:  Plain old dish detergent is GREAT at breaking surface tension.  It also breaks droplets up and allows for complete cover of whatever you are spraying, if using as a spray.

Don't need anything special, plain old dawn or palmolive works great.

--Shane
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« Reply #32 on: March 23, 2020, 12:49:49 PM »

Perfect! glad the cooling issue's resolved.

Even though this is done now, just going to throw a related or maybe silly idea on the table here, mostly applying to gear having a long-ish duct.

Longer ducts are common enough in ham-scale transmitters. The KWM-2 uses a quite long 1.5" diameter rubberized duct. Homebrews are anything goes.

The old respectable BC transmitters like the BTA-5F and BTA-10F used a cloth duct from the blower to the tube.

There were not any turns in the ducting, but the cloth would have isolated blower vibration and mechanical noises from the tranmitter or tube. The cloth should have been quiet as well. Anyone ever been around that old a transmitter? I've only seen inside one. The duct was apparently "duck cloth" or some sort of canvas, and was a little slack but not sagging and very well formed to the fit.

One possibility for this today may be to cut off part of the leg of some old "skinny jeans" (all skinny jeans should die) and use that as a duct itself if there's enough pressure, or just the lining for a duct and places where the air flows past. The thrift store may be a source.

Having made a vibration-isolating mount for a blower here, the only failing is the above mentioned metal tubing ductwork, which could have been plastic or anything - this is not yet set in stone at all.

Curves in the duct would require some cutting and sewing of the cloth to fit the shape whether as a lining or the duct itself. I do not know if 0.8 to 1" or even 2" pressure would inflate a cloth duct or if some sort of external plastic-like ribs running its length would be required.

There are not many pictures of the cloth ducting except in the old catalogs.


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« Reply #33 on: March 23, 2020, 01:28:44 PM »

Hey Shane how is the left coast? What are you working on a Telestar or a John Boy? I like what Bill Orr said and I will quote. That is from the 1979 Armature newsletters. It is on line as a PDF I can post it here I don't know if that is allowed. It is on the Bunker of doom http://www.bunkerofdoom.com/lit/Eimac_amateur_service_newsletters1979.pdf

"No simple rules can be given to accommodate all tube installations in all possible equipments. Tubes
can be damaged by lack of air, but never by too much air, unless the blast is strong enough to lift the
tube out of the socket and smash it against your ceiling! Use the largest blower you can afford. A great
deal can be learned about air flow by puffing cigarette smoke into the blower and observing the path it
takes in quitting the amplifier."

Johnathan N8QPC
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« Reply #34 on: March 23, 2020, 03:41:59 PM »


OK I canít 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 itís 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 thatís believable.


Jerry, you have an impressive QRZ page.

I was reading through your comments, and the CFM tests you did intrigued me. For those that are mentally challenged (me), could you highlight the calculations required to get CFM from the time it takes to fill a 30 gallon garbage bag? Then maybe point out tips on getting repeatable data.

Thanks,
Jim
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« Reply #35 on: March 23, 2020, 04:13:38 PM »

Jonathan,

Neither.  I like Telestar and can't day enough bad things about John Boy. Lol.

This is one built by Chris in Alabama. No regulation of any ki d....  Not even a zener in G1.

It's clean now.  Does respectable IMD.  I pick up my Hermes Lite today (hopefully) so I might be able to run some imd tests on it.

Before, G2 voltage would be 350 unloaded, 330 keyed and 320 full out.

Nice.....  Not.

It's now adjustable from 320 to 200 volts. 

--Shane
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« Reply #36 on: March 23, 2020, 04:32:16 PM »

Patrick,

I suspect the "cloth" in the RCA ad was actually fiberglass... or something like it.

Nomex might work today??

Also I think you meant to say KWS-1 not KWM-2? Cheesy

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« Reply #37 on: March 23, 2020, 11:36:47 PM »

Jim asked about my goofy flow measurement technique so I will try to answer here. I'm sure this method has plenty of measurement errors but it at least gives me a ballpark idea of flow. I made a "collector" out of cardboard that is basically just a rectangular box with the ends cut out. The collector fits over the tubes so that one of the open ends "seals" to the chassis and all the air coming out the anode fins has to go up the collector and out the other open end. I then attach garbage bag to the top of the collector with a rubber band.

With everything in place in the amp I turn on the fan (HV off of course) and use my phone as a stopwatch to measure the amount of time required to fill the garbage bag with air. Google tells us that one gallon is 0.134 cubic feet so if it takes 26 seconds to fill the bag we can calculate airflow as follows:
(30 Gal/26 sec) x (60 sec/min) x (0.134 Cubic Feet/Gal) = 9.28 Cubic Feet per second
Or simply 241.4 divided by time to fill in seconds.

To help try and achieve consistent results I always squeeze the air out of the bag before I start and I always try to lay the bag out in the same way when deflated. I stop timing just before the bag puffs up like a balloon (as in the picture) because at that point the flow is zero. With a flow rate around 10CFM it takes 24 seconds to fill so if you don't have lightning fast reflexes on the stop watch it doesn't matter too much.

I ordered my fan today. That source Shane gave me is just 3 hours down the interstate from me so it should be here in a day or two. It was so cheap I ordered 2. They also had some handy looking little transformers so I ordered a couple of those too.
73 - Jerry


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« Reply #38 on: March 24, 2020, 08:51:55 AM »

Jonathan,

Neither.  I like Telestar and can't day enough bad things about John Boy. Lol.


Are those CB amplifiers?
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« Reply #39 on: March 24, 2020, 09:04:06 AM »

Jerry, what a great photo of that garbage bag filled with air sitting on top of your amp!
 Smiley Smiley
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« Reply #40 on: March 24, 2020, 11:37:19 AM »

Jonathan,

Neither.  I like Telestar and can't day enough bad things about John Boy. Lol.


Are those CB amplifiers?


John Boy is.  Telestar made multiband amplifiers.

--Shane
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« Reply #41 on: March 24, 2020, 03:08:33 PM »

Bernoulli's principal. Increase diameter of supply hose to reduce the velocity and noise. Create a plenum box inside to transition to a smaller size hose. U might find some parts and pieces at a shop / store that sells HVAC stuff like Ferguson Plumbing Supply , HD or Lowe's. You might have to play with this to make sure the flow is adequate. Use a manometer to measure the back pressure in the underside of the chassis. U can make one out of some clear tubing if you don't have a commercial instrument. There's another post in this thread about that. ST
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« Reply #42 on: March 24, 2020, 04:23:09 PM »



so are AM'ers truly windbags, now?

 Grin Grin

Ed
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