Re: coherers

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Ed,

At 04:29 PM 8/5/2002 -0700, you wrote:
.............
>
>Terry:
>
>	What did you do with your coherer, and how well did it work?  I suspect
>that just about any conductor will serve for the filings, but that same
>may work better than others.  
>
>Ed
>

I have not seen it in about 15 years.  Could be at the bottom of pile #17,
but that would take a crew like got those guys in PA out of that coal mine
to find.  I think a 1960's "Popular Electronics" or "Electronics
Illustrated" had the project on the front cover. "build your own coherer!!"
 I will make an attempt to find it...

It was just a 1/8th inch ID glass tube from the junior chemystery set about
3 inches long.  Filling the alcohol lamp with denatured alcohol and sealing
a copper wire protruding about an inch in one side by melting the glass
tube around the wire.  Then I filed a nickle and penny (they were copper
back then) for hours to get enough to fill the tube about 75% or what
looked right.  I remember it was a heck of a lot of filing with a dull
file!  (I get power tools to do everything now :-)) I then sealed another
copper wire in the other end with the alcohol lamp.  I don't think they
make chemystery sets that use fire, alcohol or have cool chemicals like
sodium cyanide in them anymore...  And that was before Dad went to the
chemical supply house and rounded out the set with every other concentrated
acid and chemical that sounded "fun".  Eventually, Mom put her foot down
after brother Bob had an "accident" while grinding shotgun shell powder in
the mortar and pedestal...

I assume the people that wrote the article knew what they were doing.  It
was 75% nickle to 25% copper to the best of my memory...

It really did work!  One could fire a car ignition coil from 10 or 15 feet
away and the meter would show the resistance had gone from infinity to some
low values which I long forget (no tuned circuits or antennas).  I don't
know if that is good or bad.  Maybe not good enough for transatalntic
communication, but it was impressive to the young Terry.

Tesla coils an coherer circuits have had a long history together, so I
guess they are on-topic.  Like Tesla coils, I don't think any two where
ever made the same way.  I am not sure the operating principles of coherers
are understood even to this day...

A search on "google" for coherer brings up a ton of info but only light
details...  Sites that go back to Branly's original ones seem the most
detailed but are not usually in English...

http://perso.club-internet.fr/dspt/branly.htm

Cheers,

	Terry