[Amps] Fan Noise in GS-35b Amplifiers

Fri Feb 21 09:42:41 EST 2014

I believe that the numerous models of 8874 Alphas did not come from the 
factory with that fan. The back panel was punched for ventilation and was a 
convenient place to mount one.

My 76PA 3 holer came from a Carribean contest station after an operator 
induced meltdown, and the owner had added the fan, there is no factory 
harness. OTOH I may have read in one of the manuals that a fan was suggested 
for high duty cycle use. Mine has the basic EI transformer and not the 
Hypersil option which turned it into the CA.

It is a fine amp for the second station and as an AM linear at the 1500W PEP 
"legal" limit; I also switched to the much quieter EBM Papst version..

Carl
KM1H

----- Original Message ----- 
From: "Roger (K8RI)" <k8ri at rogerhalstead.com>
To: <amps at contesting.com>
Sent: Thursday, February 20, 2014 11:58 PM
Subject: Re: [Amps] Fan Noise in GS-35b Amplifiers

> On 2/20/2014 10:22 AM, TexasRF at aol.com wrote:
>> 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.
>>
>
> The smaller Alphas went that route as well.
> My 76A has a muffin fan on the back, blowing into the cabinet ans a 
> squirrel cage blower in the middle, pressurizing the tube base compartment 
> and silicone rubber chimneys to the top from the tubes.
>
> 73
>
> Roger (K8RI)
>
>> 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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