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Author Topic: Amplifier Fan Noise  (Read 10702 times)
KA5ROW
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« Reply #15 on: December 24, 2011, 12:06:32 PM »

The fan on my Kenwood TL-922A went out some years ago I replaced it with a similar size fan at 120 CFM, it moves a lot of air but the noise is not bad.
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AA4HA
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« Reply #16 on: December 26, 2011, 01:23:22 PM »

There is some really poor cooling and acoustic design out there, I think a lot of the "designers", particularly at the budget end of the market fit whatever can be had most cheaply, and may or may not look up the fan curves and get the manometer out to check back pressures.  

Fans running in blade stall are far more common then they should be, and you get silly things like fans hard up against heatsinks with no space for the flow to mix and decouple from the blades, loads of noise that way. A few inches can make all the difference and can actually increase airflow significantly.

External anode tubes tend to high back pressures, and usually need a radial blower rather then an axial fan to make sufficient pressure, they do not always get them (Radial blowers are expensive compared to a PC cooling fan).  

For real quiet you need large diameter fans and ducts so both blade speed and airflow speeds are low, but again that costs in both equipment size (Including heatsink size) and fan cost.

Be careful of attempts to muffle fans, particularly on the intake side, you can raise the backpressure easily, and that can hurt both cooling and noise levels. Lined ducts and designing plenum chambers into the equipment is helpful, but not something that is easy to retrofit.

In general when designing equipment it is better to have the fan blow air into the chassis rather then work as an extractor, most are less prone to stall if the intake pressure is as high as possible.
If the layout allows it, burying the fan inside can be a valid trick, between the power supply and RF bays is often reasonable, and the PSU bay can serve as a plenum for reducing intake noise, again not something easy to retrofit.

Regards, Dan.

You are right on the nose regarding poor design/ component/ heat sink placement contributing to very high fan noises. The loudest fan I have is on a Racal R-2412 dual VHF/UHF receiver. It is a tightly buttoned up chassis and if you are familiar with how Racal lines up all of the plugged in modules on their receivers there is very little place for the air to go. This is an expensive receiver with a terrible cooling setup so it still ends up running quite warm. A little bit of ventilation exhaust openings would reduce the backpressure and increase the airflow. You cannot just button up a chassis as tight as possible, stick a high speed fan on one end and expect the radio to not run hot.

At the other end of the spectrum are the fans on the Harris RF-350K, lots of ductwork, a gigantic air inlet (the lower half of the front of the power supply) and as long as the bearings on the fan is in great shape it is a quiet radio.

Since all of my gear is rack mounted (in a console) and about 1/3 is tube based (R-390A's, SP-600's) I also use very large 48 VDC computer fans running off of a 24 volt supply just to blow air across the chassis and IERC tube shields. At any one time, with everything powered up there are around 14 fans blowing air around equipment, through console openings and pulling the hot air out of the top of the console. In the summer I attach a piece of plastic dryer duct to a vent that blows the warm air outside. In the winter I move the vent attachment and turn around the little vent door so it sucks cold air into the bottom of the console from outside. This time of the year, when outdoor temperatures are in the 30's and 40's F the radio room stays around 78 F without opening the vent to the home heating system.

I do have an amp mounted in the console; A Harris RF-355 that uses a 3CX800A7 for about 500 watts output. (I love the 3CX800A7 tubes and would love to have a 3CX1500 based amplifier) (the design/build that is still on the drawing table). Very similar to the Ameritron AL-1500.
« Last Edit: December 26, 2011, 01:24:59 PM by AA4HA » Logged

Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
AB1KC
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« Reply #17 on: December 27, 2011, 04:44:01 AM »

I never noticed the fan noise in my Alpha until I replaced it with an Acom 2000A.
What a difference! I almost forget the Acom is running! It is much nicer to listen without headphones (my preferred operating style) now that the Alpha is not blowing up a storm.
Just my quick 2 cents.....
BB
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W8JI
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« Reply #18 on: December 28, 2011, 04:12:42 AM »

I don't understand why the  "Amateur Radio Community" puts up with the fan noise that
comes with most of the new Amplifiers, one of the most read about complaints and talked
about when discussing amplifiers.
 My old Drake L4B fan can't be heard , oiled yearly. My new amplifier is a great product
except for the whine of the fan,the loudest noise in the shack.........except when I whine about
the fan. Can't wait till the warranty expires, three more years of whine,then I going to change
the fan to something like the Drake fan. For $5000 plus it should have came that way.
Thanks for letting me whine..............

The Drake L4B was designed when the power limit was 1000 watts DC plate input power maximum. That is about 175 watts per tube average dissipation, so it is pushing maybe 500 watts of total heat, from filament, tube, and tank heating, out of the cabinet.

The Drake L4B will just barely keep the tubes within temperature limits at 600 watts carrier output power steady. The pin seals will actually go slightly over temperature ratings on RTTY at 1000 watts dc plate input.

The L4B also uses glass tubes that cool primarily via radiation, instead of forcing air across a heat exchanged like external anode ceramic tubes. It takes less air speed and turbulence to cool a 3-500 than it does an external anode tube, so it is quieter.

Do you think it is a good idea to downgrade the airflow in your new $5000 amplifier so it can move the heat of an IR radiation cooled system with 500 watts maximum heating power capacity?

This problem of hammering the tubes though power beyond design limits is exactly why people melt solder out of tube pins, and have the lettering fade on the temperature sensitive paint Eimac used, in the old kilowatt input power rated amplifiers.

73 Tom
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G3RZP
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« Reply #19 on: December 28, 2011, 06:28:55 AM »

>why people melt solder out of tube pins,<

One military transmitter I know of did that because the tube manufacturers advice on the cooling of filament seals was ignored.

Big blowers running slowly are the quietest, combined with adequate size ducts for the air to flow in. Much the same principle as for steam locomotive valve gear and their steam pipes.
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VK4DD
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« Reply #20 on: December 28, 2011, 07:40:34 PM »

Many amps are designed as if the designer at the end of the design process realises that needs a fan and just sticks it at the edge of the box or sometimes outside the box.
This result is noisy design.

These amplifiers are tipcially not the quietest ones, but some glass tubes need little air flow and that helps also.

Here are my ideas on how to build a quit amplifier.

Firstly imagine an empty room with no carpet on the floor and no curtains.
How does that sound? LOUD. Keep that in mind.

The centrifugal blowers are the quiestest ones in particular the low RPM, that is my conclusion also. EBM blowers has got some real quiet ones.

What's the source of the noise? Mainly from the air inlet of the centrifugal blowers. So do not build you blower outside or on the edge of the box. Place it in the centre with the air inlet facing down to bottom of the box. I glue felt under the air inlet and I also glue it to the lid.

The felt is damping the noise, no more loud noise like an empty room.
A very nice and quiet amp. My 3cx800 with EMB blower was build like this and you forgot it was running. My PC hard drive made more noise.  I suppose that is one of the great things if you build your own gear.

Other ideas are to stick some felt in the exhaust provided that air temperatures are low enough not to cause issues with the damping material.

It is good if the air goes around the corner, the same trick is used in the exhaust system of your motor car.

Do not modify your existing amp, keep in mind that some materials can burn or produce smoke. Contact your manufacturer always if you modify your amplifier.
You don't want to under cool it or create a fire hazard.

Last but not least, it is a good idea to mount a smoke detector in your shack.
You never know when you are going to need it.

73 Ron
VK4DD
« Last Edit: December 28, 2011, 07:53:37 PM by VK4DD » Logged
K0TF
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Posts: 1




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« Reply #21 on: December 28, 2011, 10:26:49 PM »

Can't wait till the warranty expires, three more years of whine,then I going to change
the fan to something like the Drake fan. For $5000 plus it should have came that way.
Thanks for letting me whine...
Don't whine (about the price now), get yourself decent fan http://www.ebmpapst.com/en/products/overview.html
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K4RVN
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« Reply #22 on: December 29, 2011, 07:10:32 AM »

Do these fans give fan curves or static pressure ratings for the posted CFM ratings? I saw the DB ratings which is good so one can get the lowest one that will supply the cfm at the required SP.
These are needed to select a suitable fan.

Frank
« Last Edit: December 29, 2011, 07:36:16 AM by K4RVN » Logged
M0HCN
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« Reply #23 on: December 29, 2011, 07:38:28 AM »

Ebm-Papst are good kit, the curves are in the datasheets.

Regards, Dan.
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W8JI
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« Reply #24 on: December 29, 2011, 01:00:09 PM »

The centrifugal blowers are the quiestest ones in particular the low RPM, that is my conclusion also. EBM blowers has got some real quiet ones.

That's why Ameritron amplifiers paid the bigger dollar and used EBM blowers.

If you actually measure noise, most of it is air through the tube fins. You can place the blower in the next county, and if you have the same aor flow through the fins you will have about the same noise. Some low frequency stuff will go away, but the higher energy stuff will be exactly the same.

The best idea is to cut every other two fins out of the tube cooler. That will quiet it down.
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K4RVN
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« Reply #25 on: December 29, 2011, 08:49:54 PM »

I noticed that my old 23 year old fan in the AL 80 A was made in Germany last week when I installed my glitch resistors.
 I did not look for the mfg. It has done well.
Good job Tom.
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VK4DD
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« Reply #26 on: December 29, 2011, 09:01:20 PM »

The centrifugal blowers are the quiestest ones in particular the low RPM, that is my conclusion also. EBM blowers has got some real quiet ones.

That's why Ameritron amplifiers paid the bigger dollar and used EBM blowers.

If you actually measure noise, most of it is air through the tube fins. You can place the blower in the next county, and if you have the same aor flow through the fins you will have about the same noise. Some low frequency stuff will go away, but the higher energy stuff will be exactly the same.

The best idea is to cut every other two fins out of the tube cooler. That will quiet it down.

Jim, I am starting to think real positive about these Ameriton Amplifiers.
May be for tubes with more pressure drop, but in my in experience with a 3cx800 most of the noise can from the air intake.

The 4cx250 which was very popular in navy equipment has a lot of pressure drop and needs a high speed (big pressure drop). No matter what you do, this thing will be noisy.

I never considered modifying the tube, that would be similar to running less air through it.
I know that some use 2 blowers, pressurising the Anode and a small blower or fan to cool the pins or seals. Squeezing the air through the socket is technically good but very noisy.
For professional use the way to go, but hams have different ideas and might prefer to sacrifice tube life for a quiet shack.

My old (home brew) 4cx600J HF amplifier used to be very linear and was slightly under cooled also.
I used also 2 blowers to keep the noise down. Had a few spare tubes so that was not an issue. Now that is what I call a linear tube, you don't see very often in ham gear.

By the way the professional version used 2 x 4cx600J for 1kW out. Now that is a linear amp guys. These 600J are hard to find, you mostly find the 600JB as pulls from medical equipment.

73 Ron.
« Last Edit: December 29, 2011, 09:13:21 PM by VK4DD » Logged
VE7RF
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« Reply #27 on: December 31, 2011, 03:50:35 AM »

The centrifugal blowers are the quiestest ones in particular the low RPM, that is my conclusion also. EBM blowers has got some real quiet ones.

That's why Ameritron amplifiers paid the bigger dollar and used EBM blowers.

If you actually measure noise, most of it is air through the tube fins. You can place the blower in the next county, and if you have the same aor flow through the fins you will have about the same noise. Some low frequency stuff will go away, but the higher energy stuff will be exactly the same.

The best idea is to cut every other two fins out of the tube cooler. That will quiet it down.

###  Huh ?  Phil, K5PC, and other's, tried locating the blower on the other side of the wall, and used 4-6" diam  hose to feed the air to the amp. It was very quiet. Their conclusion was most of the noise was from the blower intake, and not the air going past the tube fins.  This was on bigger tubes like 3CX-3000A7's and YC-156's.  On the big tubes, what u think are fins, are really struts, used to hold the cylindrical portion in place. If u shine a light down the inside, with the tube standing on a white sheet of paper, you will then see the actual fins..which are no thicker than a razor blade.  When they reach the outer  circumference, they fold the fins back on themselves, like a hairpin.

##  check this out, for sound proofing an AL-1500, so it's dead quiet. http://www.k6jrf.com/FT2k_AL1500.html


Later...  Jim  VE7RF
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W8JI
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« Reply #28 on: December 31, 2011, 06:23:40 AM »

K6JRF is not the most relable source. He even thinks RF is audio. He feeds audio into an RF detector, to determine or quantify how an RF detector system works.   :-)

I just went through a bunch of noise measurements while maintaining the same static pressure.
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VK4DD
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« Reply #29 on: December 31, 2011, 02:27:53 PM »

The centrifugal blowers are the quiestest ones in particular the low RPM, that is my conclusion also. EBM blowers has got some real quiet ones.

That's why Ameritron amplifiers paid the bigger dollar and used EBM blowers.

If you actually measure noise, most of it is air through the tube fins. You can place the blower in the next county, and if you have the same aor flow through the fins you will have about the same noise. Some low frequency stuff will go away, but the higher energy stuff will be exactly the same.

The best idea is to cut every other two fins out of the tube cooler. That will quiet it down.

###  Huh ?  Phil, K5PC, and other's, tried locating the blower on the other side of the wall, and used 4-6" diam  hose to feed the air to the amp. It was very quiet. Their conclusion was most of the noise was from the blower intake, and not the air going past the tube fins.  This was on bigger tubes like 3CX-3000A7's and YC-156's.  On the big tubes, what u think are fins, are really struts, used to hold the cylindrical portion in place. If u shine a light down the inside, with the tube standing on a white sheet of paper, you will then see the actual fins..which are no thicker than a razor blade.  When they reach the outer  circumference, they fold the fins back on themselves, like a hairpin.

##  check this out, for sound proofing an AL-1500, so it's dead quiet. http://www.k6jrf.com/FT2k_AL1500.html


Later...  Jim  VE7RF

The inlet was indeed the place where I could achieve the biggest noise reduction. But that doesn't mean the blower outlet is fully quiet. The outlet noise is reduced when it goes through a  labyrinth of channels in side the amp. Again different amps, different tubes different results. But Jim's idea to modify the tube will reduce some noise but not as much as noise damping materials and some work on the input will do. But beside that it will reduce the value of the tube and its specifications.  I like to remind you that any work near High Voltage is something you leave up to an expert. Any work which could block the airflow could create a fire or malfunction of the equipment. So may be you want to consider a different approach.

Location:
An other aspect we haven't discussed is strategic location on the bench top.
Some amps are quieter when they are located left or right. Some noise absorbing material outside the does something too.

I have seen Hams who placed their amp under the table with some carpet sticked under the table. A trick which will quiet down the amp too. But that's far from handy if you do a band change.

So the last one and the ultimate solution is to put the amp in a different room.
Something like the ACOM 2000 with a remote controlled display.

Or simply buy a quieter amp. If everything fails consider to put up more aluminium up outside, that works well in RX too.

73 Ron.

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