"coffelt2" wrote in message
...
There was a very large variety of microphones which
would work with this transmitter, any high-impedance mic
will do. There are still some made but I am not current
on what is available. Solid state stuff can used low or
medium impedance mics directly but old vacuum tube TX
need a matching transformer for them.
The main manufacturers of high impedance mics for
public address or ham radio use were Electro-Voice, Shure
Brothers, Astatic, and Turner. In addition American
Microphone made a line but were a smaller company.
Crystal mics are vulnerable to heat, humidity, and
mechanical shock so old ones are often not working.
Moving coil, so-called dyamic mics, are very rugged and
generally will work as well as when new if they have not
been damaged in some way. Crystal mics were popular
because they had very high output and were cheap. The
D-104 was one of the first, if not actually the first,
crystal mic on the market and has remained popular ever
since. The early ones came with a choce of flat or rising
frequency response but the rising response version was so
much more popular that the flat version was discontinued.
At least part of the sound is the result of the fairly
large baffle area of the case. This causes a diffraction
effect which increases the high-frequency output and
makes the mic slightly directional at speech frequencies,
both desireable for communication purposes.
I think its possible to get new elements for old
D-104s but I would check first, they may be expensive
since the D-104 has become a collector's item.
--
Richard Knoppow
Los Angeles
WB6KBL
D-104C had a "ceramic" crystal element which was far
more tolerant of moisture, shock, etc.
I can't remember just now what the frequency response was
(compared to the original) but when
I used one, I was looked down upon as a traitor to
tradition.
What was good about the D-104 types, was that you
didn't have to speak directly into it. One
could just walk around the shack, and in some instances,
around the house with little loss of
readability.
Old Chief Lynn, W7LTQ
Astatic and others made ceramic versions of their
crystal mics. The ceramic was, as you say, much more rugged,
but... It was less sensitive, according to a 1952 Astatic
catalogue sheet the difference was 10db! The D-104 was rated
at -45db, the D-104C at -55db. The reference is not given
but I think its db below 1 volt per dyne. The D-104 crystal
had one of the highest outputs of any crystal mic of the
time.
There was the same difference in phonograph pickups,
ceramic was more rugged and had good frequency response but
significantly lower output. In the days when amplification
was expensive the difference was important.
--
Richard Knoppow
Los Angeles
WB6KBL