Stuart has good points on using the D-104 with Tentec rigs. My experience
falls in two categories.
A good D-104 is not one that has output vs. one that does not, it is a mike
with a crystal element that has not been exposed to heat or moisture Both
cases, heat and moisture, will cause the element to become brittle and sound
bad, although it still may have output. So good is not necessarily good.
The basic D-104 head as used on a desk stand or G stand needs to see a load
Z greater than 1 megohm. Even better, something in the order of 3 megohms.
This is typically provided by tube type input circuits. Most radios today
provide a 10K to 50K input impedance which is much too low for the D-104
element. Although some have been successful, I do not advocate the use of a
transformer on a mike input due to the susceptibility of hum being
introduced from nearby AC fields. One can use the D-104 head on the Astatic
TG or TUG stand, the one with the transistor amp in the base and this will
work, as the FET amp is basically serving as an impedance converter to
provide the correct load to the mike and still be able to drive the lower Z
inputs of most solid state radios. A word of caution when using the TG or
TUG stand. It can easily overdrive the audio input stage in the radio.
Once this happens, no amount of reduction of mike gain on the radio will
clear the reported distortion.
It is also reported that, depending on wiring of the TG or TUG stand
switching, the PTT activation also turns on power from the internal 9V
battery to the amp. Often the result is a DC transition resulting in a big
whump or pop or thump that is fed to the radio input. This can saturate the
input stage which may require several seconds to recover depending on the RC
constants in the input stage.
All of these "ills" have been encountered or observed by me and often heard
on the air. The typical result leaves the operator with disgust saying the
mike is bad or the radio is bad or a host of other ills when the general
fault is poor application of the elements, otherwise not understanding the
needs of the mike or the radio.
Here is a website that covers most of the wiring conventions of the D-104
and TG or TUG stands. http://www.qsl.net/wa2mzf/d104.html
----- Original Message -----
From: "Stuart Rohre" <firstname.lastname@example.org>
To: "Discussion of Ten-Tec Equipment" <email@example.com>
Sent: Thursday, December 20, 2007 2:08 PM
Subject: Re: [TenTec] New Omni VII....first impressions
> Mike, if you have the very oldest D 104, the bad audio reports you
> describe are typical of an impedance mismatched D104. It is a high
> impedance mike. To use it for modern low to medium impedance SSB mike
> inputs, you need a matching transformer, or an emitter follower preamp to
> step down the impedance from the 100,000 ohm range to say 600 ohms. Then,
> the mike will sound great. I use the D104 very successfully with Ten Tec
> rigs with attention to matching.
> Stuart Rohre
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