On Friday, April 7, 2017 at 8:19:54 PM UTC-4, DoN. Nichols wrote:
On 2017-04-07, wrote:
Yo Jim -- and anyone else who may be interested.
I spend an hour last night tracking down some noises in my furnace
blower, using my usual piece of aquarium hose stuck in my ear g, and I
wondered if there might be a market for an advanced kind of mechanic's
stethoscope -- something that ought to be a piece of cake for someone
like you.
Maybe something like this is on the market. If so, forget it. If not,
consider this:
I had two noises, from different sources, and the interference between
them made it all but impossible to find the origins of the noises. One
was some mechanical interference between the centrifugal fan and its
housing, at one end of the armature shaft; the other was vibration
resulting from stickiness in the centrifugal throw-out switch (a
fail-safe switch that prevents the gas valve from opening), at the other
end of the shaft. I finally took the whole thing apart and found both
problems, but it wasn't easy to find them when the motor wasn't running.
Hmm ... makes me think of a mechanic's stethoscope which I used
to have which might have helped here. Instead of having the usual
stethoscope "Y" to direct one sensor to two ears, it had a separate hose
from each earpiece, which went to a round plastic pillbox with a hole
and nipple in the center of one side, and a threaded nipple in the
center of the other side into which a length of 1/8" brass rod screwed.
At the end of the rods were corks for contact to the device.
This gave a stereo signal, so you could tell which sensor was
louder and thus which was closer to the source of the noise.
That sounds nice and simple. I really like simple. d8-)
So, I wondered about the idea of making a small, cheap,
battery-powered amplifier, with a mike and a headphone jack, that
contained a couple of active, adjustable audio filters, one high-pass
and another low-pass. Made a notching filter or bandpass filter to make
it slick.
Instead of a microphone, use an old phono cartridge with a brass
whisker where the needle normally was held. (Ceramic or Crystal
cartridge -- not the fancier stereo cartridges of higher quality and
lower stylus force which came later.) Astatic was the brand of one of
these types. I wonder if you can still find them on eBay?
Nope! Nothing old enough. What you need should be mono, with a
single pair of terminals, and a thumbscrew in the front to lock the new
stylus (or the brass rod) into.
I don't play with engines much these days, but I can recall times when
such a device would have made quick work of tracking down engine noises.
There it is. If you make it and sell it, the idea is yours. Watch out
for patents.
It sounds interesting -- and more so if you can do stereo
pickups with old phono cartridges. :-)
Enjoy,
DoN.
I think I have a couple of those old phono cartridges in the attic somewhere. With my pack-rat tendencies, I usually save the old one when I put a new thingy in.
What I *don't* have is much ambition to pursue things like that. If it isn't fishing. photography, or boat gear, I try to avoid it. Time is becoming precious.
But thanks for the thoughts. I really like the stereo stethoscope idea.
--
Ed Huntress
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