[Amps] Quiet Cooling

[Will Matney]

Hal, and others,

There may be a way of using baffles with an internal enclosed fan. 
Speaker cabinet construction uses some features where acoustic engineers 
design a majority of them in industry. That would be a good person to 
speak with if we could stir one up. Suppose a high output muffin fan 
were placed in an acoustic deadened enclosure using available sound 
deadening materials. There's some foam sheet available really cheap for 
this at Parts Express (http://www.partsexpress.com/). Another thought 
would be to make the amp chassis like large speaker and guitar amps and 
or speaker enclosures using the leather look vinyl, etc. I have to say, 
I have always wanted one built this way as they really look good 
compared to plain painted aluminum, or steel chassis. This way, any ugly 
enclosure could be made exceptionally good looking with exceptional 
sound deadening. A 1/4" plywood carcus with the black vinyl cover, black 
or chrome corner guards, black anodized face plate, white silk 
screening, would be the berries. A standard bright aluminum skinned 
chassis underneath for shielding would be all thats needed. Scuffs, etc 
on the aluminum or steel wouldn't matter. An example would be the Cobra 
2000 11 meter transceiver. They had a plywood cover with a woodgrain 
veneer, which looked sharp, over a plated steel chassis. Even an amp 
with a good varnished plywood cover would make the aesthetics very good 
and deaden sound. If the air was routed around correctly, and the fan 
placed correctly, I think it would be a good bit what were wanting.

Mounting the blower remotely has always been a good option to get rid of 
noise and is easy to do using clothes dryer or vacuum cleaner hose. This 
hose is pretty cheap and available from McMaster Carr and other vendors. 
On large amps, the exhaust can be routed out of the building via dryer 
hose and a dryer vent. I've done this myself on amp projects, one using 
a 4CX5000 back in 1988.

Another insulation material that could be mounted around a fan, away 
from major heat would be foam board used in home insulation. This stuff 
is really cheap in 4" X 8" sheets. This would effectively deaden noise 
radiating from the fan itself. If the output air hit some baffling 
before coming out of the chassis, it too should die down to an 
acceptable level I would think. Anymore, you cant hardly here automobile 
engines run because of insulation under the hood and on the firewall. 
Open the hood, and you can then hear it.

A good method of cooling in an amp would be blower cool the tubes, then 
use a fan to blow across the transformer, the power supply, then the 
tank circuit on its way out. One amp in particular, though illegal, did 
have a very good cooling scheme like this. The Kenrich Eagle 515 used a 
back mounted muffin fan blowing first over the control circuitry, then 
the transformer, through the driver stage, the the final stage, and out 
the side of the chassis. The air was routed by baffles made of aluminum 
sheet. It went through the chassis in the shape of a U. When running, it 
could barely be heard but you could easily feel the output from the fan 
at the vent hole in the side. If anyone here could take a look at a 
picture of one of these, you'll see what I'm speaking of. If interested, 
I could do a drawing of how this was and save it as a jpeg. The 
manufacturer was a Ham and was doing this back in the 70's until the 
very early 80's. This was a well thought out design and probably the 
best I've ever seen for these amps.

The methods your mentioning in organs could certainly be used on a 
remote blower which could feed several pieces of equipment.

Will Matney


Sirs,

The thread about quiet cooling of amplifiers made me think back to
my college days when among studies of alcoholic consumption,
music appreciation and techniques for attracting YL's I studied
pipe organ construction and repair.

The musicians do not want to hear the air blower mechanism when they're
keyboarding and neither does any audience or congregation.

What pipe organ builders do is to isolate the blower in another room
and use a "wind-column" to supply the wind chests under the pipes
with pressurized air.

Could not this technique be applied to amplifiers? Remove the noisy
blower from the shack and connect flexible hose to a clamped fitting
on any equipment needing cooling. A much beefier fan could be
employed than would fashionably fit on a rear apron, and a 
manifold system could be arranged so that more than one piece of
gear could benefit

Hal
W4HBM