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Author Topic: Cooling a pairCooling a pair of 3-500zg tubes  (Read 480 times)

G3XLB

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Cooling a pairCooling a pair of 3-500zg tubes
« on: June 13, 2021, 04:08:25 AM »

Please could anyone familiar with building 3-500zg  linears help or advise me as I am getting very confused over blower output measurements.I am cooling my tubes identical to the Ameritron AL82. The blower is mounted above chassis and air is directed through a hole to the Eimac tube bases.I am using the correct Eimac bakelite bases and Eimac glass chimneys.Using a portable anemometer the air flow through the bases is approx 75 ft/minute but if I measure in the cfm r ange  I get a very lowreading below 1.I am just not understanding cfm and the maths.!
While testing recently one of the 4-400A tubes (old tubes picked up at rally) overheated and filament burnt out.As the tube was old could have been due to age but this has made me wary as I don't want to risk my new 3-500zg tubes. Unfortunately I can't get info on my Blower to find air specifications but does 75.0 ft/min sound reasonable ?
Any help or advice would be really appreciated Many thanks,
73,  Mike G3XLB
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W9IQ

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Re: Cooling a pairCooling a pair of 3-500zg tubes
« Reply #1 on: June 13, 2021, 05:00:08 AM »

It is very difficult to use an anemometer for this purpose. The more typical technique is to measure the static pressure in the chassis and then consult the blower curves to determine the CFM. What is the make and model number of your blower?

The spec sheet CFM rating of the blower is for open air. Once you put an impedance in its airflow, the CFM will decrease. The curves for the blower depict this relationship.

- Glenn W9IQ
« Last Edit: June 13, 2021, 05:04:38 AM by W9IQ »
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

G3XLB

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Re: Cooling a pairCooling a pair of 3-500zg tubes
« Reply #2 on: June 13, 2021, 06:01:54 AM »

Glenn,
MANY THANKS for your reply.The Blower was made byAlcatel, model number RLS97/0042.Label states 240V 44W There is also the following figures 3020LH-439. I have also seen pictures of a similar Blower made by Ideal but don't know the Ideal model number.
To date I have drawn a blank with ALCATEL.
Any ideas thanks Mike
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KM1H

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Re: Cooling a pairCooling a pair of 3-500zg tubes
« Reply #3 on: June 13, 2021, 09:07:55 AM »

A 44W blower moves far more air than you need even thru that somewhat restricted socket which is far better than the original Eimac aluminum socket

Carl
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W7CXC

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Re: Cooling a pairCooling a pair of 3-500zg tubes
« Reply #4 on: June 13, 2021, 10:08:42 AM »

KM1H   +1 That should be way more than needed. More is better! Noise?  David
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W9IQ

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Re: Cooling a pairCooling a pair of 3-500zg tubes
« Reply #5 on: June 13, 2021, 10:33:19 AM »

Glenn,
MANY THANKS for your reply.The Blower was made byAlcatel, model number RLS97/0042.Label states 240V 44W There is also the following figures 3020LH-439. I have also seen pictures of a similar Blower made by Ideal but don't know the Ideal model number.
To date I have drawn a blank with ALCATEL.
Any ideas thanks Mike

Does the discharge have a rectangular flange or is it more like a round tube?

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

W7CXC

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Re: Cooling a pairCooling a pair of 3-500zg tubes
« Reply #6 on: June 13, 2021, 10:48:57 AM »

It's round see .....google.com/search?client=firefox-b-1-d&q=3020LH-439
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W9IQ

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Re: Cooling a pairCooling a pair of 3-500zg tubes
« Reply #7 on: June 13, 2021, 11:05:50 AM »

That blower is available under a variety of names but I believe it was made by (now) EBM-Papst. Unfortunately, curves are not available.

We could estimate based on current comparable EBM-Papst models. Are you up for taking a static pressure measurement of your amp chassis? It involves a ruler, clear plastic tubing (larger fish aquarium air hose) and some water. I can give more details if that interests you.

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

G3XLB

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Re: Cooling a pairCooling a pair of 3-500zg tubes
« Reply #8 on: June 13, 2021, 12:01:42 PM »

Glenn,
The output is approx 2 inches round.
Thanks to all who replied,yes I thought 44W should be more than enough air,but started to worry when the 4-400 burnt out but it could well have been through age.
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W9IQ

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Re: Cooling a pairCooling a pair of 3-500zg tubes
« Reply #9 on: June 13, 2021, 12:20:51 PM »

Glenn,
The output is approx 2 inches round.
Thanks to all who replied,yes I thought 44W should be more than enough air,but started to worry when the 4-400 burnt out but it could well have been through age.

The typical first order estimate for the impedance of an electronics enclosure is that it will cut the CFM in half.

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

KM1H

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Re: Cooling a pairCooling a pair of 3-500zg tubes
« Reply #10 on: June 17, 2021, 08:38:18 AM »

Thanks to all who replied,yes I thought 44W should be more than enough air,but started to worry when the 4-400 burnt out but it could well have been through age.

The 4-400A family from the 65 to 1000 suffer from seal leakage plus anode outgassing from age.
Just turning on the filaments can make an internal mess if the tube has gone to air and excessive internal gas release can cause a big arc when HV is applied.

Regettering can sometimes restore a tube to use.

Carl
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K8AXW

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Re: Cooling a pairCooling a pair of 3-500zg tubes
« Reply #11 on: June 27, 2021, 09:18:12 AM »

Mike,

I have felt your anxiety about losing your expensive 3-500Z tubes!

FWIW....I built an amp 38 years ago and presently use the original Eimac 3-500Z tubes.  The blower I use is a Dayton brand, No:50747-49G, Type IC180.  115V @ .48A.  It has a squirrel cage impeller that measures 2.75" X 1.5".  It has a 2" exhaust hole, round flange.  RPM unknown...but it's kind of loud.  :D

The blower is mounted on the chassis rear apron with a thick rubber gasket and rubber grommets. The exhaust feeds a "wind box" inside the chassis which feeds the air input holes in a pair of Eimac aluminum air sockets, Eimac chimneys and anode radiators.

For perspective, remember there are hundreds of Heath amps still in service that uses a simple fan blowing air across the tubes!


I don't think you have anything to worry about.  I sincerely hope you get the satisfaction from your labor of love that I had the past 38 years.

73

Al - K8AXW
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A Pessimist is Never Disappointed!

K3UIM

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Re: Cooling a pairCooling a pair of 3-500zg tubes
« Reply #12 on: June 27, 2021, 09:48:23 AM »

Al,
"I sincerely hope you get the satisfaction from your labor of love that I had the past 38 years."

And that's what it's all about!!

No matter what the hobby, the sense of satisfaction that comes with a successfully completer project is never understood, or appreciated, by the average person. So many give up after trying something because of the amount of work, research, etc involved, whereas the project finisher truly knows the "thrill" of a job well done. (Perhaps this is where "trolldom" came into being?? LOL)

A great example could be marriage! It takes a LOT of work! I could be wrong in some cases, I guess, but 60 years, in my case, certainly proves my thought. LOL {Most of the work on Lois's side, I must admit.  ::) ;D}

Enough before I get myself in trouble!! Hi

Charlie
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Charlie. K3UIM
Where you are: I was!
Where I am: You will be!
So be nice to us old fogies!!

K8AXW

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Re: Cooling a pairCooling a pair of 3-500zg tubes
« Reply #13 on: June 27, 2021, 09:13:56 PM »

Love her....hug her....compliment her...I lost my wife of 59 years and 10 months two years go.  The regrets never go away Charlie.

As for the amp, it's my masterpiece.  If you or Mike needs something to do, read and see at:

http://www.arrl.org/news/build-your-dream

73

Al
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KM1H

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Re: Cooling a pairCooling a pair of 3-500zg tubes
« Reply #14 on: June 28, 2021, 08:45:52 AM »

A very nice amp Al.

One comment about glass vacuum variables is that seal leakage does occur from age. Ceramic versions are fine for now.

Carl
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