D-104 Element Internal Parts - FYI

[WBear2GCR]

Attached ought to be a close up image of a ~1977 D-104 crystal element, with the upper aluminum diagphragm (what you talk into) removed (carefully).

This particular element has zero output.
I was hoping to repair it.
It isn't the wax connection to the diaphragm - the other element was repaired by fixing that, not this one.

Anyhow, the foil lead on the right seems to go under the red plastic to the foil on the bottom... the lead on the left actually doesn't seem to go anywhere at all. I looked at it under a high power eyeloupe and still couldn't discern a connection. Perhaps there is a sandwich with the red plastic, but I don't see it. Where the "Rochelle Salts" are, I dunno...

         _-_-WBear2GCR

[WBear2GCR]

Additional reading online now leads me to believe that the "crystal" is in fact the square red thing that I thought was plastic. Ha! 

Will have to probe for a "^" pivot mount at the bottom center point... it's not obvious, but theory would place such a thing there... diagonally opposite the yoke on top and on the opposite side there are two rubber pads going to the bakelite body... I had assumed that they were the mounting points, maybe not.

Images of Rochelle Salts show a clear translucent crystal material.
More modern ADP crystals appear to be greenish... why this is red in color, I don't know...

Still not quite understanding where the left most electrical connection point wants to be...

                _-_-bear

[k4kyv]

The first time I bought a replacement element from Astatic, many years ago, I pulled away and threw out the yellow "packing material" that was stuck to the front of the diaphragm.  Then I noticed that somehow the diaphragm had got damaged, with a hole poked through it, although no other damage was visible. I "repaired" the hole by plugging it up with a drop of epoxy.

Later I figured out that the "packing material" was actually a disc of fibreglass insulation designed to damp out metallic resonances in the diaphragm.  The hole was punched there intentionally, to equalise the atmospheric pressure on both sides of the diaphragm.  I don't know why Astatic didn't pack a notice to that effect along with the replacement element.  I'm sure I'm not the only person who has ever done that.

Moot point, because now they won't even sell the replacement element.  They want you to send the whole mic to them for repair.

[WBear2GCR]

Hey Don,

Afaik, Astatic is not supporting the mics any longer - but that is second hand info.

The image that I posted is the innards of the element, under the aluminum diaphragm, fyi.

                 _-_-bear

[w4bfs]

I have been experimenting with 'walkman' earphones which are typically 30 or so Ohms.  I have put 3 of these in series and then using an old Shure autotansformer from a dual Z mic, raising the impedance up to 10kOhm or so ... use a dc blocking cap (.5 ufd or so) to keep dc off the xfmr ... works very well ... be sure to use some open cell foam as it pixk up breathing pops/noises ...all this to replace unobtanium D104 cartridge ... beefus

[WBear2GCR]

You can buy a "replacement" crystal element made in Asia, that is passable.
Not sure but I think it can be had from either Mouser or Digi-key.

Otoh, the heads are still plentiful at hamfests... as are the mics...

                    _-_-bear

[Rob K2CU]

Bear,

The square part is the crystal itself. the conductive strips connect to foils plated on either side of the cyrtal element. To repair, you will need to get conductive epoxy to reasttach to the foil. See:

http://www.mgchemicals.com/products/8331.html

There are several other products available.

It is expensive stuff in any case due to the silver component.

It is impossible to solder the leads as the salt melts at 75 C.

Mouser carries two Kobetone crystal microphonium elementiums, 25LM024 and 25LM022. The 024 is closest to the D104 element in size and frequency response. So much so, that you would think it was intended to be their version of same.  It is a pretty rugged package and I bought two for insurance on my own D-104.

Crystal earpieces that came with crystal radios of the '50s also contain a Rochelle salt element. You might consider harvesting one if all else fails.

[WBear2GCR]

My problem is that I do not see any attachment point for that upper foil at all!

If I saw where it belonged, I'd have a go at it.

There's no way to solder to aluminum anyhow... and it looks to my eye that the foil is merely wrapped on the crystal, and coated with some sort of varnish like material...

Step two will be removing the crystal from the rubber mounting blocks and getting "up close and personal" to see where things are supposed to be attached.

Unless someone here can post a diagram of how this style is set up, or knows where those foil leads were originally terminated. I sure don't see the spot (yet) even looking with a 9x magnifier!!

            _-_-bear