Steve Thompson wrote:
>Gary McAdams wrote:
>> My question is: Would it be advantageous to add additional cooling via
>> something like added muffin fans on the sides pushing air into the amp?
>> Or would that just be a waste of time?
>It might be useful - but not necessarily because of any effect on the
>amount of airflow. Air is like water, and follows the easiest route,
>This means it goes past and round objects, often leaving a layer of
>still air on their surface. Still air is a good heat insulator. Sucking
>air tends to produce this sort of flow. The air coming out of a fan is
>turbulent, and this can increase cooling effect by increasing the
>contact between moving air and the hot surface.
Steve is right. The turbulent air from the outlet of a fan makes a huge
difference to the cooling efficiency.
If you follow a thin streamer of smoke through a typical flat-pack fan,
the streamer holds together as the air flows smoothly into the fan - but
on the other side it vanishes, completely mixed in by the turbulence. A
thin thread of cotton held in the air-stream shows the same effect.
With an extractor-type fan, the tube sits in smoothly flowing air, which
mostly takes the easy way through the wide open spaces, just as Steve
says. A thin surface layer of hot air tends to stick to the glass
surface of the tube, acting as an insulating blanket that keeps the heat
in. Meanwhile, the valuable fan turbulence is being completely wasted
into the room. In every sense, this arrangement sucks.
If the fan is upstream of the tube and blowing air onto it, the
turbulence scrubs away that insulating blanket. The glass is in direct
contact with cool air, and the surface temperature is much lower.
If users want a quiet amplifier above everything else, that fan
turbulence is a hugely important asset - absolutely not to be wasted.
But the tube isn't the only thing that needs to be cooled. Most modern
desktop amplifiers use 'full-flow ducted cooling', which draws cool air
inward past the transformer, electrolytics and other parts of the power
supply, before blasting the air directly at the tube(s). This tends to
place the fan somewhere inside the middle of the cabinet, which helps to
reduce noise. Finally, the hot air should be ducted directly out of the
cabinet - not blasted at the tank circuit.
It isn't easy to get all of these things right. Every plan has problems
as well, so we're looking for the best possible compromises.
73 from Ian GM3SEK
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