[TenTec] Astatic D104 mic and Pegasus

[Bill Fulling]

Hello Paul,
Have been using a D-104 with my Jupiter for the last year and have gotten
nothing but good comments on the audio from the many DX stations I've
worked.
This D-104 was purchased at a local hamfest three years ago when I was using
a Scout-the amp had been removed but it worked great with the Scout.FYI,from
the 1936 ARRL handbook,the info on the D-104 is -1 meg load Z @.02 volts.
Now the Scout has an input Z of 100K max-
this means a 10/1 Z mismatch.
The Jupiter and Pegasus have a 50K max
input Z-a 20/1 mismatch.
Solution? I built a FET pre amp in the base of the D-104 in common drain
cvofiguration and used a Heil XT-1  mike xfrmr wired in reverse
 with the 43 ohm windinding as the load for the FET and the 1300 ohm winding
feeding the Jupiter.Intially had to run hr mike gain no greater than 9% of
extreme flattopping would occur as observed on my good old Heathkit monitor
scope.
Solution? Pop the bottom cover off the Jupe and adjust the internal mike
gain pot for a good Christmas tree pattern into a dummy load at 50% front
panel mike gain setting.
Now what's rocket science about this?
73 de Bill W4NJF

Bill Fulling
w4njf at email.midflorida.com
----- Original Message -----
From: "Paul Christensen, Esq." <w9ac at arrl.net>
To: <tentec at contesting.com>
Sent: Wednesday, March 12, 2003 4:14 PM
Subject: Re: [TenTec] Astatic D104 mic and Pegasus


> > The crystal D-104 needs a very high (> half meg) input resistance else
> > it gives a weird frequency response.
>
> It's weird anyway and the harmonic distortion produced by the crystal
element is very high.  This is not necessarily a bad thing as
> the distortion component can oftentimes be used to one's advantage...like
DX pileups.  If one wants extension down to 100 Hz which
> can be accomplished with the Pegasus and Jupiter, the typical crystal
cartridge really requires >5 Megohms of loading.  It's
> absurdly high.  As the loading lessens (more Megohms), the equivalent
noise of the circuit can become problematic...and may be more
> susceptible to R.F.
>
> For the past ten years, I have been using a modified D-104 with a MPF-102
JFET used as a voltage follower.  The input  Z to this
> transistor is about 11 Megohms and I add about 1 Megohm of series
resistance with the transistor's Gate.  As a VF, it's gain is
> always less than unity but the output from the element is already more
than ample.  However, this entire lash-up will be put on the
> shelf as soon as my Ten-Tec Studio One mic arrives.
>
> -Paul, W9AC
>
> _______________________________________________
> TenTec mailing list
> TenTec at contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec