My experience had been that there were only TWO kinds
of muffin fans that can be added to the back of an Alpha
amp.
1) Quiet ones that make no difference in the actual
temperature of the exhaust air.
2) Noisy ones that push a lot of air and can drop the
exhaust air by as much as 10 deg F or more.
On my own 87As I had some muffin fans that I added
that were very effective but noisy. During my tenure
at Alpha/Power I decided to see if there was a muffin
fan out there that moved enough air to lower the
exhaust temp significantly and was still relatively quiet.
Finding a muffin fan that can work into a back pressure
and still be quiet is not an easy task.
I found ONE model of muffin fan that I was happy with and
that is what Alpha began supplying. If you are not using
this muffin fan then your amp is probably either noisy
or not really being helped all that much by an auxiliary fan.
I found that the exhaust air was reduced by about 8 deg F
by these two models.
The 115v quiet model is a Papst 4530Z,
and the 230v quiet model is a Papst 4580Z.
And if you really need a lot of extra air movement then
the 230v higher flow (noisy) Papst 4650Z and the
115v higher flow (noisy) Papst 4600Z is the answer.
They are quite a bit more noisy but are probably the
best if a lot of extra air is needed.
The exhaust temps were measured with a thermometer
in the air stream on top of the amp during normal contest
operation. Typical values on the Alpha were in the 140+ deg F
range.
73--John W0UN
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