[TenTec] D104mods

[Bob McGraw K4TAX]

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 at 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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