A month or two
after I made my
to the New Jersey Antique Radio Club on mounting mineral crystals for
Marv Beeferman ask if I’d examine two detectors that he had
a box lot at the Henry Ford Museum auction last year. He
two brass cylinders about an inch and a half in diameter.
a hard rubber base with two brass pins.
When Marv first obtained these
covers were tightly jammed on the bases, making it impossible to
their function. I’m sure if any
had seen the insides, they would not have been in a box of
When Marv carefully opened the cases, he found two marviously
crystal detectors, neither of which involved the usual galena and
The first detector
contained a small piece
showing the unmistakable red-orange color of zincite (zinc oxide), in
with a second mineral sample. This is the classic perikon
The second mineral is probably Bornite, Cu5FeS4,
but it’s hard to make a positive identification without
By the way, zincite is a rare mineral except in the Franklin area of
New Jersey. (Local interest.)
The second detector
consisted of a piece
lead-grey material, held in a carefully machined clamp, in contact with
a hairpin-shaped flat metallic spring. After consulting
vintage radio books andA Field Guide to Rocks and Minerals
Frederick H. Pough,
I identified the mineral as Molybdenite, MoS2,
of the Telefunken Company.
I carefully cleaned the
contact surfaces of
both detectors with isopropyl alcohol and tried them in my laboratory
The perikon detector showed a
very weak signal
from local powerhouse WOR. Tightening down on the thumb screw
things. Tightening some more, resulted in still louder
All in all, its performance was about what I had expected from my
ok, but not nearly as sensitive as Galena or a modern germanium
As a rough comparison, I’d say it works about as well as a
detector just barely worked,
repeated adjustment of the contact. The application of a little DC bias
to the detector, provided by a potentiometer
across a pen-light battery, brought the ancient semiconductor to
Performance was about on par with the perikon unit.
Detectors of these kinds were
applications because of their ruggedness. A galena detector
a very delicate touch from the catswhisker, making it a poor choice for
use on a vibrating ship in rough waters. Also the rectifying
of a galena detector can be easily destroyed by a distant lightening
or RF from the transmitter.
Because of the materials and
style employed, I’m guessing these detectors were built
era for commercial or experimental application. They were
made in the United States, as the screw threads are standard SAE types.
If any of our readers have
on these units, Marv and I would like to hear from you.