It is interesting to see how subjects can morph. Let me try to
clear up a little, and say where I am leaning now.

First, in both my original post, and my first reply to Trevor, I
was insistent that I had a 12V fan in there. I asked if I could
use a computer fan its place. That is where the whole 12V issue
got started.

But Trevor was right and I was wrong. I have a 115VAC fan. It is
the Torin A450, and my quick Google search got me the Torin
website, but it did not find anything resembling this fan. I do
know that at full voltage it is very fast and very loud.

James Bongiorno updated and replaced the circuitry in my Ampzilla.
When I asked about quieting the fan, he was unsure, as it was not
original and he did not know the model. He did state that the amp
required very little cooling, and that an extremely slow turning
fan would be just fine. He suggested a couple of different values
of resistors to try. I found it very awkward trying to attach a
resistor to very stiff solid core wiring, so stopped with the
first resistor I tried. It makes the fan very slow and quiet, and
keeps the amp cool enough, but it often does not start at all at
turn-on. Is this called a "hystersis effect?"

I have simply lived with this problem for a long time, until
recently deciding to seek advice on what to do about it. I recall
that in the past I had trouble finding the resistors that
Bongiorno recommended, and did not really feel comfortable
interpreting the packaging. That is why I originally expressed
interest in either some sort of potentiometer (which I now
understand to be a bad idea in this application) or else a
replacement fan that is naturally slow and quiet.

As an aside, some months ago I set off on another quest to quiet
down my computer. In my reading on that subject, I gained the
strong impression that German made Papst fans are the Holy Grail
of quiet computers. I also learned they are almost impossible to
find in the US and wound up with some different solutions, mostly
from Zalman, a Korean company.

Anyway, an email from 'tater' gave me a large number of fan links,
and I learned that Papst is marketed in the US under the ebs
Industries label. My current fau is 119 x 119 x 38mm. Papst
makes a number of fans in that same size, and I chose one rated at
28dBA that turns slowly and moves only a little air. Digikey
wants about $30 plus $4 shipping for the best one I could find for
my purposes. Papst seems to make some still slower and more quiet
fans, but I have not found a US source for those models.

My current thinking is to put in a Papst/ebs fan and remove the
resistor. I hope that will be quiet enough. If it is not, I
suspect a much lower value resistor will do the trick. Before
taking that step, I will return to these groups for advice.

Thanks everyone for all the help, and a great deal of
entertainment as well!

Phil Anderson