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SVT Cooling Fan: Push air in, or pulls air out?

Groover

Groover

Jun 28, 2005
1,756
19
Ohio, USA
#1
Is the cooling fan on a vintage SVT supposed to push air in from outside, or does it draw it out (like an exhaust fan)?

If you have an SVT, could you check please? Mine is set to push air in the amp, but the fan cowling has brass grommets on the other side as if it should be mounted the other way...

I think it's supposed to push in like I have it, but I'd like to double-check.

Thanks.
 
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#4
NKUSigEp said:
Always have it so the fan is blowing air out - the main idea is to suck heat away from the tubes with a secondary effect of pulling in cooler air through the other side.
Click to expand...

blowing air directly at what you are cooling is better than pulling it away.

In multi-fan setups it can be usefull to have fan/s pulling air away and out to have an effect an ambient temps. But in a single fan setup you don't have that luxery. Blow directly at what you are cooling.
 
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#5
The fan should always pull hot air out of the chassis. This will create a vacuum and move air away. A fan blowing air from the outside might not reach the same place. So instead of mixing the hot air (until it stays the same temp) you will pull it out.
 
#8
Pulling air through a restriction (ie, an amp and tubes and stuff) is easier and more efficient than pushing air through a restriction. Pull-through allso allows for more evenly dispersed cooling, because as mentioned above, creates a slight vacuum and ambient pressure causes more air to rush in and replace what is removed.
Just like your car radiator. The fan is behind the radiator and pulls air through it. Much more efficient than if the fan were in front of the radiator and pushing air through.
...but sometimes things are designed the other way for whatever reasons...it'll still work regardless....
 
#10
Toptube said:
blowing air directly at what you are cooling is better than pulling it away.
Click to expand...

You don't work around electronics much do you? This may be true in an open space, but that's not what we're dealing with.

Foxy_Moron said:
The fan should always pull hot air out of the chassis. This will create a vacuum and move air away. A fan blowing air from the outside might not reach the same place. So instead of mixing the hot air (until it stays the same temp) you will pull it out.
Click to expand...

+1

eastcoasteddie said:
Pulling air through a restriction (ie, an amp and tubes and stuff) is easier and more efficient than pushing air through a restriction. Pull-through also allows for more evenly dispersed cooling, because as mentioned above, creates a slight vacuum and ambient pressure causes more air to rush in and replace what is removed.
Just like your car radiator. The fan is behind the radiator and pulls air through it. Much more efficient than if the fan were in front of the radiator and pushing air through.
...but sometimes things are designed the other way for whatever reasons...it'll still work regardless....
Click to expand...

+1


As smart as the engineers at Ampeg are (or were, rather), you would think they could have gotten the fan direction right. I've only owned 3 SVT's but all have had the fans installed incorrectly. The tubes would have much better ventilation (and longer life) if the air was drawn out instead of blowing in. It almost makes me think they conspired with tube manufacturers to increase business.
 
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#13
got my first SVT a year ago and went through the same dilemma. my repair guy put in a new fan for me cuz it was noisy and weak, and he switched it from blowing out to blowing in. i read on TB and elsewhere and the basic answer was that Ampeg had changed directions at different times. i don't know scientifically about electronics and radiators, etc, but the fan seems to work better now that it's blowing cool air on the tubes. seems more logical to me that the heat would rise out of the back than straight towards my face. also blowing dust into the grill seems illogical.
 
#15
Ok, didn't realize this was such a controversial topic!

Thanks for the replies. Sounds like mine was mounted pointing the right direction after-all (blowing air in).

However, after reading the mixed opinions here, it seems that either way will work fine, so now I will share my findings on some SVT fan mysteries which may help someone in the future.

This experiment is based on an SVT-HD (skunkworks) with original Rotron fan, and perforated rear panel - that said, YMMV

Test-1) Fan mounted with air pushing in headbox (factory intent from what I learned here):

- The pros to this is that it sticks with designers intent, which I'm not dicounting the fact that they mounted the fan this way after some R&D, concluding this would be the best air flow for this amp.

- The cons to this are: Pushes a lot of dust into the amp making a mess in there. This particular fan mounted this way creates a high pitch whirling noise (as some refer to a jet plane taking off sounds...) - The whirling noise is the fan blade being too close to the perforated panel, and drawing air in to head, apparently creates this phenomena... One way to drastically reduce the whirling almost to the point that it's all gone, is to use longer mounting screws and put mounting spacers between the fan and the perforated grill - 3/8 to 1/2" should do.


Test-2) Fan mounted with air blowing out (reverse from factory intent):

- The pros with this configuration are cleaner environment on the inside (and this is just an assumption, and not tested as it would take many years probably to see the difference). However, the big pro IMO here is that the fan mounted this way just sounds like a fan... No crazy whirling sound going on, and no spacers required to achieve that.

The cons to this setup.... Well, you would be going against how Ampeg R&D'ed it, so whatever happens, you're on your own. The other con is that the slightly uglier side of the fan would be visible when you peeping through the rear panel's holes...

----

I'm currently restoring this amp and I'll have plenty of time to decide how to put the fan back in. One thing for sure is that if I keep it with the airflow pushing in, I'll be using the spacers to kill the whirling noise.

Thanks again. I hope this helps.
 
#17
I think that Ampeg has the fan blowing the way that they do simply for aesthetics.

If the fan were exhausting hot air out the back of the amp, dust would accumulate at the intake on the front grille cloth. This wouldn't look very good.

Better to look good, than to be concerned with tube life.
 
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#18
Sounds like ignorance prevails yet again. :rollno:

Exhausting air out would be the more efficient way of cooling tubes, end of story...but hey, not all of us have the benefit of being electronic technicians and engineers that actually know what we're talking about. Because something is a certain way, doesn't make it the right way.
 
#19
beans-on-toast said:
I think that Ampeg has the fan blowing the way that they do simply for aesthetics.

If the fan were exhausting hot air out the back of the amp, dust would accumulate at the intake on the front grille cloth. This wouldn't look very good.

Better to look good, than to be concerned with tube life.
Click to expand...
i agree, especially after seeing the dust circle that accumulates on old svt-cl's ;)
 

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