Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1] 2 3 Next   Go Down
  Print  
Author Topic: Amplifier Fan Noise  (Read 9077 times)
WB0MCO
Member

Posts: 81




Ignore
« on: December 23, 2011, 10:52:04 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..............

Merry Christmas,Happy New Year To All




Logged
M0HCN
Member

Posts: 473




Ignore
« Reply #1 on: December 23, 2011, 11:21:18 AM »

Part of it is the push to ever smaller boxes, which means more backpressure, which means louder fan.

Part of it is the move to more solid state kit that needs to run the heatsinks cooler then the glass fets did, which means more airflow and a louder fan.

Part of it is 'value' engineering and the use of fans which cannot sustain the backpressure required and stall the blades resulting in lots of airflow noise (PC style Axial fans where a snail blower is really required), plotting the pressure curve and doing the graph plotting to check the operating point falls somewhere sensible on the pressure/flow curve for the candidate fan is apparently too much like actual engineering.

Regards, Dan.
Logged
N6AJR
Member

Posts: 9890




Ignore
« Reply #2 on: December 23, 2011, 01:46:29 PM »

you could always put a muffler on it.  A short piece of 5 inch diameter cardboard tube with so sound deadner in it   slipped over the fan intake may help  a bit.
Logged
WB2WIK
Member

Posts: 20545




Ignore
« Reply #3 on: December 23, 2011, 02:03:24 PM »

I wouldn't arbitrarily replace a fan or blower with a different one, without knowing a lot about the comparative ratings, including air flow against actual back pressure.

Most of the "noise" from cooling systems in amplifiers, unless something's vibrating, is just the sound of air movement through restrictions.  Less noise = less air movement, which could potentially = failed components.

Be careful.
Logged
M0HCN
Member

Posts: 473




Ignore
« Reply #4 on: December 23, 2011, 02:29:04 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.
Logged
W8JX
Member

Posts: 5474




Ignore
« Reply #5 on: December 23, 2011, 03:40:14 PM »

I wouldn't arbitrarily replace a fan or blower with a different one, without knowing a lot about the comparative ratings, including air flow against actual back pressure.

Most of the "noise" from cooling systems in amplifiers, unless something's vibrating, is just the sound of air movement through restrictions.  Less noise = less air movement, which could potentially = failed components.

Be careful.

I agree. RPM of fan and blade design has a big effect on back pressure performance. Higher RPM fans tend to be nosier but handle back pressure better. Squirrel cage blowers are quieter for air moved and back pressure handled but are a lot bulkier too.
Logged

--------------------------------------
Entered using a  WiFi Win 8.1 RT tablet or a Android tablet using 4G/LTE or WiFi.
KD0UN
Member

Posts: 55




Ignore
« Reply #6 on: December 23, 2011, 07:02:19 PM »

I'm far from an expert on the subject, but I'd guess part of the issue is the output expected out of the tubes.  My old 2K-4A is barely audible, but it isn't rated at 1500 watts output.  When the two 3-500's are put in a 3K, more air is needed to save the tubes, and my understanding is that there is much more noise.

I'm actually surprised eat the output folks advertise from their used L4Bs, and other 3-500 combos.  I seem to get only about 12-1300 out at maximum, but that's with tubes about 35-40 years old. 
Logged
W8JX
Member

Posts: 5474




Ignore
« Reply #7 on: December 23, 2011, 07:27:27 PM »

I'm actually surprised eat the output folks advertise from their used L4Bs, and other 3-500 combos.  I seem to get only about 12-1300 out at maximum, but that's with tubes about 35-40 years old. 

I think some of them are padding it a bit. In the case of the L4B, it is not that the deck is not capable of 1.5+kw put rather that the stock power supply is not. With a updated power supply with more voltage a L4B can easily exceed 1.5kw.
Logged

--------------------------------------
Entered using a  WiFi Win 8.1 RT tablet or a Android tablet using 4G/LTE or WiFi.
K4RVN
Member

Posts: 758




Ignore
« Reply #8 on: December 23, 2011, 10:05:55 PM »

Dan, 2eoche,
I doubt seriously that many amps have fans that actually enter the stall point on a fan curve as little or no air would be provided and the tubes would overheat. I just have to think that designers would run a test to see what the actual static pressure drop was through the air path in the amp and would use a suitable fan. As you know, the CFm is directly proportional to the rpm according to fan laws and I believe the mfgs. just use fans with rpms too high to be quiet because they are cheaper than going to a larger diameter. Also the size constraints of the cabinet play a part I think. I have noticed some on the forum discuss fans, especially axial fans without regard to the static pressure ratings. The fine print may sometimes read at zero static pressure so they are not selecting a fan to suit the pressure drop needed to supply adequate air for the amp. You made some valid points so I think you understand the fan requirements.
« Last Edit: December 24, 2011, 07:14:32 AM by K4RVN » Logged
AD6KA
Member

Posts: 2232




Ignore
« Reply #9 on: December 24, 2011, 07:24:00 AM »

Quote
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.

I have been a ham for 25 years and have NEVER
had anyone tell me "Gee your amp fan sounds loud".
(Always had Ameritron Amps).
By the same token, in 25 years I have NEVER had to
tell ANYONE: "Say again, OM? Couldn't copy you because
your amp fan is too loud".

Then again there are those annoyingly loud T/R relays......Grin
I think the emperor has new clothes.

73, Ken  AD6KA
Logged
WX7G
Member

Posts: 5920




Ignore
« Reply #10 on: December 24, 2011, 07:36:58 AM »

I use active noise cancelling headphones to GREATLY attenuate fan noise.
Logged
K9ZM
Member

Posts: 13




Ignore
« Reply #11 on: December 24, 2011, 07:48:36 AM »

When you say "whine" I think something different than the rush of air associated with a cooling fan.  My solution was to contact the factory to get the procedure for changing the speeds in the firmware.  Of the three speeds available, the fastest got rid of the whine noise, which to my ears was irritating.  I have a soft air rushing noise now, which is much more acceptable and expected to my tastes.  Amp stays cool and I am much happier.  And I thought my Henry was quiet when I bought it years ago.  Compared to the 6 meter amp it's noisy.  But the Henry is much quieter than the Dentron's and Amp Supply I had prior to it.   
Logged
M0HCN
Member

Posts: 473




Ignore
« Reply #12 on: December 24, 2011, 11:06:40 AM »

I don't know about full on stall, but I have seen 120mm axial fans making an awful lot of noise with remarkably little air movement.

There is at least one manufacturer of amps using external anode tubes over here that cools them with a single 120mm fan sucking air out of the anode compartment....
Probably just about enough for UK legal SSB (400W PEP), but I really would not want to try it in a RTTY contest while playing fast and loose with the license power limit (We all know people like that).

"Engineering" like that is why I tend to build my own gear or convert ex military/commercial kit.

High pitched whine is sometimes a sign that someone has perpetrated a rather crude PWM controller, you might find that a series resistor with the fan fixed on full speed will get you a happy medium.

Logged
K1ZJH
Member

Posts: 901




Ignore
« Reply #13 on: December 24, 2011, 11:52:26 AM »

This is one of the advantages of going deaf in old age.... What fan noise?   Grin
Logged
W7ETA
Member

Posts: 2528




Ignore
« Reply #14 on: December 24, 2011, 12:01:00 PM »

I've heard rumors that some have used flex tubing, like for a dryer, to route the exhaust away from their microphone.

I always use headphones that cover my ears.

Best from Tucson
Bob
Logged
Pages: [1] 2 3 Next   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!