[Amps] Fan Noise in GS-35b Amplifiers

[TexasRF at aol.com]

Jack, many homebrewers hang the blower off the rear panel to allow  
pressurizing the entire amplifier cabinet. That certainly gets the cooling job  
done but with maximum blower noise.
 
Another approach is to locate the blower inside the amplifier and only  
pressurize the tube from the bottom. Ameritron AL1200,1500 and maybe others 
work  that way and have much lower blower noise.
 
My homebrew vhf and uhf amplifiers are built that way. There is a three or  
four inch diameter hole in the rear panel for air intake. The hole is 
covered  with a K&S round air filter to keep dust and bugs out. The filter 
further  reduces the noise and keeps the amplifier clean as a whistle inside.
 
73,
Gerald K5GW
 
 
 
 
In a message dated 2/20/2014 6:51:43 A.M. Pacific Standard Time,  
w9gt at frontier.com writes:

Yes,  that Dayton blower is a good one to use, however, it is still quite 
loud even  with the slower speed.  Of course, you can reduce the fan speed on 
 receive, but when transmitting, the noise is objectionable.  I'm  
wondering if slower speed and higher volume really translates to adequate  cooling 
if the actual air pressure is not there.  Many blowers will  provide what 
seems to be adequate air flow, but with back pressure, just don't  provide 
sufficient flow.  I have seen several European hams' GS-35b amps  with what look 
like just "muffin" type fans.  Those things are pretty  loud anyway and I 
don't think they move enough air.  I have seen  examples, also where they are 
using two "muffin" type fans.....one above the  anode cooler pulling air 
out of the enclosure and one below the chassis  blowing upward thru the tube.  
There has to be some of you folks out  there who have a "quieter" solution??
73,  Jack,  W9GT


________________________________
From: N1BUG  <paul at n1bug.com>
To: Jack C. Shutt <w9gt at frontier.com>;  "amps at contesting.com" 
<amps at contesting.com> 
Sent: Thursday, February  20, 2014 9:26 AM
Subject: Re: [Amps] Fan Noise in GS-35b  Amplifiers


I don't know what the "recommended" blower is,  but bear in mind slow speed 
blowers can be much less noisy than high speed  ones. They tend to be 
physically larger, however. On some prior amps I used  high speed (2500-3000 RPM 
I think) blowers that were physically rather small.  They got the job done 
but were very noisy. On my current generation 4CX1500B  amps I use Dayton 
2C647 blowers. They run at 1500 RPM, but move about the same  amount of air by 
using a larger squirrel cage. They are much quieter. I  suspect even this 
amount of noise would be objectionable to many people but  those blowers are 
far less noisy than the 4" fan in my rack mount server case  that houses the 
shack PC. Something has to be done about that  fan!

73,
Paul N1BUG


On 02/19/2014 11:07 AM, Jack C. Shutt  wrote:
> I have gathered from all the info that I have read on amps  using
> the GS-35b that a healthy air flow is necessary to keep  these
> tubes happy.  Unfortunately, the 100 CFM squirrel cage  blower
> that is recommended for this purpose is quite noisy.   Any
> suggestions for an effective cooling arrangement that is  quieter?
> I thought about remotely locating the blower and using a  hose
> duct to the amp, but this is just not practical in my  shack.
> Suggestions?   73,  Jack,  W9GT
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