I was doing some digging online and didn't come up with much on the topic. Could someone point me in the right direction to some articles/papers on the thermodynamic, electronic, mechanical, audible effects (or variations) in building an amp "tubes up" vs. "tubes down"?
Any findings/based on your experiences you'd be willing to share are greatly appreciated too!
hmm...not sure you'll find much beyond common sense and conjecture. HiFi amps & other chassis-at-the-bottom amps need adequate ventilation, which isn't provided by the classic Marshall head. At some point in time, the Marshall boys added the beer-strainer vent on their 100W amps. The 50 watters needed it, but didn't get it. You won't see too many Marshalls run with the rear panel attached.
The Fender tweeds and blackface amps, appear to believe in heat rising, to move the heat away -- so the tubes are close to the rear 'wall.' Vox amps appear to believe in convening all the heat inside a cabinet, then placing pathetic small vents above...and hoping for the best. Ampeg put a fan in the SVT, much like any sensibly built solid state power amp. QSCs draw from the front and push air out the rear, iirc. Certain morons have built power amps that pushed the air sideways in a rackmount product.
Back to basic science, the glass near the base of a power tube is supposed to be the hottest, so allowing heat to rise up, into or against a chassis seems ill conceived.
Last edited by jaysg on Wed Mar 31, 2010 2:29 am, edited 1 time in total.
In most cases for consumer audio, up or down, it doesn't matter.
There are for some power types recommendations when it comes to
horizontal orientation, which socket pin number should be up to ensure the
longest operational lifespan. If its a tube type and or application that is a
real investment, I'd check all the data sheets and with the maker, some hi fi
types are well worth the search. Most data sheets are fairly easy to find but you
have to scour the data for notes on the sheet.
Tube makers generally didn't express any concerns over whether the bottles should face up or down.
As Andy mentioned there were certain tubes where their use in a horizontal plane was either discouraged, or recommended only with the tube oriented in such a way that pin 'x' was at the top.
I think it all comes down to the design of your chassis and head case whether heat is going to present an issue or not.
I'm not a big advocate of fans because, unless the airflow path is carefully designed you can end up with comparative cold spots on some of the tubes which further stresses the glass envelopes, especially if you have a fan moving a lot of air.
In things like the SVT I can see why they need it though because they've got a fairly small head case with two chassis' installed, one tubes down and one tubes up, 14 tubes and 6 of these being 6550s working hard.
Even then a linear fan across the width of the chassis with a low air pressure would probably work better than the small fan running at high speed that's going to cause a very concentrated flow of air through parts of the amp.
