[Amps] Fan Noise in GS-35b Amplifiers

Roger (K8RI) k8ri at rogerhalstead.com
Thu Feb 20 20:23:34 EST 2014

On 2/20/2014 9:51 AM, Jack C. Shutt wrote:
> 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??

Most tubes are listed as so many CFM at so many inches of water 
pressure. That pressure is "required" with no interruptions to get that 
flow to cool the tube at its rated dissipation.  This assumes you have 
sufficient cooling on the seals.  Generally the air into the tube socket 
compartment is directed at the tube seals. Some sockets direct a portion 
of the air over the seals.


Roger (K8RI)

> 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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