[SMCARA] Mic

[William S Merritt]

One more point about Rochelle Salt crystals: They are also sensitive to
mechanical shock.  So, handle those D-104's in a reasonable manner and
don't use them to crack walnuts while waiting your turn on the round
table!  :)  bill KB4QAA




On 2/26/2015 12:10 PM, Clarke, Tom AIR4.0P NATOPS wrote:
> Hi Larry,
>
> They're as common as hydrogen at any Hamfest!  I saw a bunch at Richmond. Not sure when the next Hamfest is in our area.
>
> BTW, the D-104 has a Rochelle salt crystal element that is very susceptible to heat and moisture damage.  Even if you get a dud, it is a simple job to replace the element.  The original elements are no longer available from the EOM, Astatic, but using an electret element
> from Radio Shack (if you hurry before they disappear!) works well.  A more elegant fix is to use the Heil retrofit kit for the D-104 and you will have a great sounding mic.  Kobetone used to make a replacement crystal element, but it is no longer available (maybe on eBay?).  Using the electret or the Heil element makes the amplifier in the base of the stand redundant.  The original intent of the preamp was to match the Hi Z of the crystal element to the Low Z input of modern rigs.
>
> Actually using the preamp with a Low Z element will make it sound awful, due to overdriving the input stage of the radio.  The original element likes to see about 2 to 5 Megohms of load in order to sound good.  Feeding it into a Low Z input will roll-off most of the lows and it will sound "tinny" and distorted.  All ham radio gear of recent vintage (i.e., anything after the "tube" age) likes to see about a 600 Ohm load and that is what the electret or Heil will present.  The electret needs bias circuitry, whereas the Heil dynamic element is a drop in replacement and does not require bias.
>
> I have an original D-104 crystal mic that I use on my Collins 32V3 and Heath DX-100 tube type, "Boatanchor" rigs, and another with the Heil mod for my K-3. They both sound great.
>
> Talk about a long answer to a short question!
>
> 73 Tom/W4OKW
>
> -----Original Message-----
> From: SMCARA [mailto:smcara-bounces at mailman.qth.net] On Behalf Of Larry Norris
> Sent: Thursday, February 26, 2015 9:49 AM
> To: SMCARA at mailman.qth.net
> Subject: [SMCARA] Mic
>
> Looking for D-104 Desk Mic
> Larry Norris
> N3JTN  Ham
> Leonardtown,Md
> You can't have too many radios....
>
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-- 
Bill Merritt
KB4QAA/3