Read W9AC D104 mod on eham
-----Original Message-----
From: Bob McGraw K4TAX
Sent: Monday, April 30, 2018 10:05 PM
To: tentec@contesting.com
Subject: Re: [TenTec] D104mods
Here is about the most complete compilation of D-104 and related G stand
information.
http://www.qsl.net/wa2mzf/d104.html
Historically the D-104 used a Rochelle salt crystal element. This
element has a high output voltage and it required a very high impedance
input, typical of a tube type input. The input impedance should be in
the order of several megohms, typically 2.2 to 4.7 megohms. Most
solid state radios do not have a sufficiently high impedance input to
effectively work with, what I'll describe, a virgin D-104 element.
Most modern radios have a microphone input impedance in the order of 50K
ohms or less, some much less in the order of 10K ohms.
Thus along came the G-stand being the T-UG8 which contained a transistor
circuit in its base. While there is some amplification in the circuit,
there is primarily the ability for the D-104 element to "see" a very
high impedance, yet the output of the circuit is designed to drive much
lower inputs, typical of most modern radios. It is also very easy for
this circuit in the base to over drive, or drive into distortion, the
first input stage of a modern transceiver. In this case, the MIC gain
on the radio will have little to no effect of improvement. The mike
signal must be reduced in the T-UG8 base via the level control accessed
via a hole on the bottom.
The issues encountered with the original Rochelle salt crystal element
is the fact it was prone to damage by heat {never place or leave one in
the sun or hot environment} and moisture being condensation on the
element from one's breath or a few balls of errant saliva from the
mouth. Either or both will damage the element. Hamfest D-104 mikes
and G stands are always suspect. While some say "it works OK", yes it
may have output, but frequency response deterioration is the first sign
of damage and one may find "they work" but may sound rather unpleasant
an unnatural.
I've noted many places and companies do offer "replacement" elements.
In some cases they are actually putting a dynamic element in the D-104
housing. In come cases they us and elecrect or condenser type element.
Franky and factually, I view this is no longer a D-104 in the
purest sense and doesn't sound like a D-104.
The original D-104 has the Rochelle salt crystal element, the D-104C has
a ceramic element having a bit more durability but less output and
somewhat different frequency response, and then there is a mobile hand
mike carrying the D-104 series identification.
The G-Stand has its own history. Several different versions and several
different switching arrangements are found in the link supplied above.
Most of those versions are shown from the original G-stand to versions
of the T-UG8 stand. The link above describes most of those iterations.
To find an original D-104 with a T-UG8 stand in pristine condition is a
real pleasure to have displayed on the shelf. {With this said, there are
much better sounding and performing mikes to use on modern radios.}
73
Bob, K4TAX
On 4/30/2018 8:21 PM, Paul Gates wrote:
You are right I have about 4 D104s. When we moved recently I put the head
of the D104s in a sock.
On Mon, Apr 30, 2018 at 20:42 Rodney <w3krq@dejazzd.com> wrote:
I been getting emails about why D104 mods what do they do, the mod
changes
the impedance from high to low w6ac made a very good mod but he quit.If I
was younger I would make these mods there is a lot of D104 out there.
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