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Sunday, July 9, 2017

Have You Ever Seen What's Inside a D-104 Crystal Element?

I had not seen this  I must say, I am disappointed.  I had visions a circular collection of shiny Rochelle salt crystals.  But look at this thing.  It is quite flimsy -- not at all what you'd expect from the sturdy D-104 exterior.  It has kind of a "Wizard of Oz" behind-the-curtain feel to it.  Yuck. If I can't find a D-104 element in good shape, I might reach for a dynamic element or -- gasp -- an electret.

6 comments:

  1. Hi Bill.
    The D-104 element looks to be about what I'd expect, from experience with the internals of piezo guitar pickups and old telephone ringer, mic and earpiece transducers, so I'm not disappointed at all. In fact, it almost looks resurrectable!
    I take it the top 'cup' is shown upside-down in the background there. Can you compare the original diaphragm with cooking foil? or perhaps a common plastic film ex-packaging from the household refuse? If not too different, I'd venture some of that across the 'top', then that inverted back in place just might do the trick. The 'pillar' of the 'stirrup' might be too high unless you can pre-stress the foil to the appropriate amount to also pre-stress the crystal just enough (or maybe not - is the pillar top flush with the rim of the bottom 'cup' with the original diaphragm glued to the pillar?)
    Jeweller's precision required, methinks?

    73
    Dex ZL2DEX

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  2. Hi Bill,

    I was wondering, that element is very similar to a crystal ear piece that you would use for a crystal, only larger, correct? Why not take the guts of a crystal ear piece and put it in place of the old unit? It may not be stock, but at least it will be functionally the same.

    73

    Dean AC9JQ

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  3. The equivalent Astatic dynamic mic is a 10-DA. It includes a step-up transformer in a pretty chrome housing. Almost impervious to humidity, unlike the D-104.

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  4. The equivalent Astatic dynamic mic is a 10-DA. It includes a step-up transformer in a pretty chrome housing. Almost impervious to humidity, unlike the D-104.

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  5. Thanks for the pic! My guess is that there are numerous piezo benders that could work well with the mechanical structure of the D-104 diaphragm cone. It looks like the crystal is supported on a point in the middle of the back and the little "stirrup" bracket on the front transforms cone diaphragm linear motion into bending action on the crystal. Looks like the stirrup is attached with Glyptol or some similar hard drying glue. Probably the same stuff on the back of the crystal at the attach point. The difficulty will be putting it back together with good mechanical coupling from the cone to the stirrup...and without introducing resonances or breaking the glue. The hand built look of this gives some insight into why some D-104s perform better than others. Good luck and thanks!
    Mike WO1U

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  6. Uh, oh. No updates in a few days.
    I smell a Franken-phone.
    Yeah, I'd put an electret and a one transistor pre-amp on there. Use it for my BitX40, but I just like tearing things up.

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