Just for reference, where does info on the mic come from?

I worked in engineering there for over 20 years so I have a little inside
info on it :-)
Since it's probably not documented anywhere, here is probably more then
anyone ever wanted to know about it…..
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As mentioned, amplified versions started in the 70's mainly to be compatible
with newer "transistorized" radios with low-z inputs.
That was indeed at the beginning of the "power mic" craze. The first
transistorized version was the T-UG8-D104.
Later came the T-UG9-D104 (adding more switch contacts and wires), and the
"Golden Eagle" which was a gold plated version done for the U.S.
Bicentennial. It also featured an eagle engraved on the back of the D104
head.
The Golden Eagle was so popular that the Silver Eagle version was created
(the Golden Eagle was a limited edition). It was actually a T-UP9-D104 and
added a push bar on the bottom as well on the side (Thus the "P" in the
model number).

There were both crystal (Rochelle salt) and ceramic versions of the D104
head, but the crystal version was always the most popular.
At one time Astatic made some of the crystal elements in house (fun to
watch), but only to supplement those made outside. The crystal element
consisted of two slabs of Rochelle salt, graphite, and gold leads that were
wrapped in foil and encased in epoxy. If you look at an old spec sheet, you
will see the “foil wrapped” crystal mentioned. This was supposed to improve
the life of the crystal. Rochelle salt has a high moisture content and after
a period of time the crystal will dehydrate and no longer operate, so it
must be well sealed and stored in a cool environment. The capsule had a
bakelite housing and an aluminum diaphragm. Except for the newest versions,
the diaphragm was attached with rubber cement and a special black wax that
was made in-house. To tame the huge resonant peak at around 2.5KHz, a round
disk of fiberglass insulation was glued to the front of the capsule. This
stuff, which we called “Magic Puff” (because it worked so well), was
actually aircraft insulation and either yellow or pink.

Eventually sources for the crystal started to go away. The company changed
hands in 87 and when I left in 2000, the only source for the crystals was
from a small company in Austria. This company made the crystals for the two
remaining crystal mics, the D104 and the various versions of the old JT-30
bullet harmonica mic, for a number of years.

My understanding is that the company in Austria finally folded, and so
production on those two mics finally ceased a couple of years ago.

At one point I did play with creating a dynamic version of the D104, but the
project never flew.
The original head consisted of three pieces. If you wanted to try to put
something like a ribbon inside one, the thing to do would be find two of the
older heads and use the front screens to create a head with screens on the
front and back.

The newer heads are only two piece (The back and middle section were die
cast as one part to save money).

Robert