On 2/20/2014 10:22 AM, TexasRF@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@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@n1bug.com>
To: Jack C. Shutt <w9gt@frontier.com>; "amps@contesting.com"
<amps@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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