"Phil Anderson" wrote in message
news:9ztZa.78172$cF.24225@rwcrnsc53...
Thanks to everyone for the replies. You've helped me to get
further down the road toward figuring out what to do. Here is
what I know now:
The current fan is a Toran A450, rated at 115V and 0.25amps, if I
am reading it right. The size, in mm, is 119x119x38.
Papst fans seem to be almost impossible to find in the US. They
are marketed in the US under the name EBM Industries, but even
knowing that does not seem to help a lot.
My Ampzilla barely needs a fan at all. I do not use it all that
often nor all that long. With the current fan barely spinning, it
will run forever without becoming too hot to touch.
So, I guess my first question is whether I should even replace the
fan at all. With the current resistor, I have to 'finger-start'
the fan, but once it is going, it is completely inaudible to me.
Even if I find a Papst, it cannot get quieter in any meaningful
sense. Yes, I can understand that a better fan will move more
air, resulting in a cooler amp, and still remain inaudible, but I
do not feel I need anything cooler than what I have right now.
Still, if I could find a high-quality, slow turning fan that will
run inaudibly without the need for resistors, thermisors,
rheostats or wombats, I would be happy to go that route instead of
trying to find a way to reduce the voltage to the current fan. I
very much like the idea of simply screwing something in, attaching
two wires, and declaring victory.
**You really don't have much choice.Besides, it is not that difficult.
You've tried one resistor and the fan does not quite start. Reduce the value
of the resistor by (say) 20% and try again.
So, my first question: Is there a good source for such fans? No
bells, no whistles, just the right size and slow, quiet turning.
To emphasize what I said above, airflow is not really an issue. A
little is enough.
Sub-question: What is a good brand name, assuming I cannot find
Papst/EBM in the US.
**Most are decent enough. Look for a nice cast alloy chassis and ball
bearing races.
Second question: Does size matter? I am guessing that whether
the replacement is 25mm thick or 38mm think won't matter in this
amp. But what about that 119 x 119 part? I have seen listings
for 118 x 118, 119 x 119, and 120 x 120 (all without prices, BTW).
Are all these fans interchangeable, or does a single millimeter
matter?
**Nope. I said 120mm, but the actual size is 119mm. 119mm is a standard.
Looking at the airflow, you'll note that 120mm fans move around double the
amount of air as the next size down. Stick with 120mm and run it slower.
Third question: If I do not replace the current fan, what is the
SIMPLEST way to confidently regulate the speed of the current fan?
While most of you have figured this out already, let me make it
plain in case anyone has missed it. I am not an electrician. Not
only do I not play one on TV, I have never met anyone who plays
one on TV. I have replaced plenty of outlets and light fixtures,
and even a ceiling fan or two, but my mind simply does not seem to
grasp concepts much more complex than that.
**I suggest you play around with different resistor values. You have tried
value X. Now try 80% of X. Or thereabouts.
If I keep the current fan, I would like an alternative method of
speed control that meets the following criteria:
First, it should involve little more than splicing a device into a
wire.
Second, it should not involve a great deal of trial and error. I
really do not like the idea of picking up a half-dozen resistors
and swapping them in and out until one works just right.
**Why? It's easy, cheap and it'll work. Other methods are going to require
that you do a lot more work.
Third, it should be SIMPLE. I understand why temperature
sensitive devices may be the BEST solution, but I do not see how
to make them the simplest. What temperature do I want?
**You want the fan to kick off, at around 40oC. You want the fan to be
running reasonably hard at 50oC. You want it to be REALLY running at 80oC.
How do I
find a device with that temperature setting? Where do I put the
sensor?
**On the heat sink, close to the output devices.
What other questions am I missing? Given that I do not
understand this whole process all that well, going this route just
seems to me to be an invitation to error; a way for me to screw up
without even knowing it.
**Just drop your present resistor size by 20%. That should work fine.
That is why the idea of a rheostat, or something with a knob I can
turn or a switch I can flip between positions, appeals to me. If
I find the right device, I should be able to splice it in place
and then adjust the speed until I am sure it will spin up when
power is applied, but won't spin loudly enough for me to hear more
than a foot or two away.
**Not practical, since you are dealing with mains Voltages. Keep it simple.
Either use a different resistor, or buy a temperature sensing fan.
In summation, and having gone on much too long already, I want
either or both of two things:
1. A source for a quality, slow turning, quiet fan, and/or
2. Advice on speed-controlling the current fan in the simplest
possible manner.
Thanks again,
Phil
PS. It is really a shame this is not a 12V fan, as there are all
kinds of solutions in the computer world, including, possibly, the
120mm Antec Smart Fan I added to my Sonata case.
**12 Volt DC fans are difficult to control. They have internal circuitry
which regulates the speed. Varying the input Voltage, is not very
successful.
--
Trevor Wilson
www.rageaudio.com.au