marshall mg100hdfx fan direction

[raven45227]

hello all, i have been installing new fans in my two heads, yes i have two of these. i noticed that one model of this amp from 2004 has the fan blowing into the heatsink, while the 2005 model has the fan blowing away from the heatsink and also has a shroud. i am confused as to why you blow away from the heatsink seeing it as small already. i have thought about making my own heatsink but bigger. lol if anyone could let me know about this i would greatly thank you. jim

[soundguruman]

It's probably better as exhaust. Otherwise you are blowing hot air from the sink INTO the amp.

[Enzo]

Cooling is about air flow. How much air can you push past the heatsink. There is supply air, typically from the outside, and exhaust air, which is typically vents somewher. WHatever is drawn into the amp must have a way to leave. Otherwise you just pressurize the amp and no air FLOWS.

If you have a tunnel with something in the middle needing to be cooled, it really doesn;t matter which end of the tunnel the fan lives in.

[soundguruman]

on this amp, the sink is energized (bzzzzzzz) , and the fan is the insulator
and so for the insulator reason, the fan has to be on the correct side

[Enzo]

That is true. But it is also totally irrelevant to the question of which way the fan should BLOW. And that was the original question being asked.

[soundguruman]

OK the way I see it the fan blows out, it draws cool air through the chassis first, then over the sink.
if it blows in, the heat from the sink goes into the chassis, and heats up the rest of the components.
So it does make more sense blowing out first.
What really kills the MG 100 is driving 4 ohms, it's gotta be 8-16 or it gets too hot.
Or that bloody zeener diode blows and shuts down the whole thing, but that is neither in or out.
And I think some silver compound on the output IC would not hurt either. That's my choice and I do it that way.

[Jazz P Bass]

My 2 pence.
The one without the shroud/tunnel should blow in.