Why fans? Why not proper passive cooling?

[alexclaber]

I remember a lot of bassists getting paranoid about the older SWR amps which had no fans and relied on the aluminium casing acting as a heatsink/radiator, thus causing the casing to reach temperatures which would otherwise indicate imminent failure in a conventional steel-cased fan-cooled amp. I don't know if SWR changed their approach due to this paranoia or for cost reasons but I suspect it was a bit of both.

[PlungerModerno]

[quote name='Jack' timestamp='1344946713' post='1771437']
It's not really loud at all but the amp is also my home practice amp if I'm not using headphones.

I'm a computing enthusiast and I'm currently 2 feet away from a huge metal box with 3 140mm fans, 2 120mm fans and a 180mm fan. Id guess the GK was easily twice as loud, and at a much more annoying frequency (likely because of the amp's fan's smaller diameter).
[/quote]

I guess it depends on the fans and the ambient and running temperatures.
Page 9 of: [url="http://www.gallien-krueger.com/productmanuals/160-0540-A%20MB%20FusionManual.pdf"]http://www.gallien-krueger.com/productmanuals/160-0540-A%20MB%20FusionManual.pdf[/url]
Quote "Continuously variable fan cooling"

So does that mean (and it mightn't) if the tubes are hot the fans are loud... which, combined with the full voltage on the pre tubes... wait:


Cool Running = Reliability: To cool the amp
when its being driven hard, we’ve designed a
temperature sensitive fan cooling system. When
the amp is under a light load, the fan is off or
running at a low speed, reducing fan noise. As the
amp works harder, the fan speed increases to keep
everything cool.

Well I guess that means loud fans .

[VTypeV4]

[quote name='Bill Fitzmaurice' timestamp='1344911314' post='1771008']
Where valves are concerned keeping them cool isn't of any benefit, keeping the heat they create out of the other components is.
[/quote]


Still odd tho as all the components with the exception of the mains transformer, output transformer and supply choke are buried below the chassis. Even those on top are sited away from the valves.

Either way, I guess the designers thought it to be a required part of the amp. If it makes it last longer then thats peice of mind for me.

[flippyfloop]

[quote name='fretmeister' timestamp='1344767617' post='1768834']

Just as an example, the new Markbass Big Bang. It's tiny, even smaller than a LM3 and I bet the fan is whirring like a bastard.

[/quote]
Not really

[PlungerModerno]

[quote name='Spoombung' timestamp='1344781811' post='1769035']
I hate fans in amps. Absolutely NOT necessary.
[/quote]

I'd imagine you'd need crazy passive cooling for any high powered all valve head - My GK mb fusion gets warm, I figure a lot of it is the tube pre section (when driven the fan seems to switch on earlier, even if the master is pretty tame.

The fan is noisy - like a standard computer PSU fan to my ears - not a problem unless you're getting a mic close to the head and are playing at very low volumes. Or bedroom practice. Even at moderate volumes it's buried in the noise floor.

[3below]

High powered valve head and passive cooling should be possible. How high powered are we going? Simple solution is a 'birdcage', complying with current regs about mesh size (what can / can not be inserted lol) combined with making the footprint large. For the more trad look (Hiwatt/Marshall etc) starting point will be back and front of amp are open at the lower parts (above control and output/mains plate) with the typical expanded mesh found on valve amps. Top is also extensively open with mesh. Inside you would have a stand off aluminium reflector plate above the chassis (say 5mm above), this would have some thermal insulation board below it to reduce conduction into the chassis and hence internal components. It could have slight curvature like electric fire? Layout should space the power amp valves as well apart as possible. Aluminium plates fixed at the sides of amp to channel convection currents and minimise radiation transfer into transformers. Must dig out text book on thermal transfer calcs if I have a sleepless night.

Edited September 29, 2012 by 3below