[Heathkit] Looks like a D104 Project Cont.

[Jim Shorney]

On Wed, 14 Feb 2007 20:35:22 -0600, Robert & Linda McGraw (K4TAX) wrote:

>Here is about the most complete source of reference data that I've found. 
>It is nicely presented too.
>http://www.qsl.net/wa2mzf/d104.html


Good info, but I should point out that according to my reading, the crystal
element in the D104 has a very high impedance - on the order of a megohm or
more.  An old-timer's trick when using a D104 with a non-amplified stand is
to add a 470K or higher resistor in series with the audio lead.  This mellows
out the audio response and improves the low end, helping to eliminate that
"tinny" sound that some people hear.  I've used a so-modified D104 on my
Drake TR7 with good results - one local I checked it with preferred the sound
of the modified D104 over a Shure 444, which is considered to be the mic of
choice for this radio by many ops.  Somewhere on the internet are charts
showing the response of the D104 element vs. load impedance, Google should be
able to turn up the info.

I personally dislike mic preamps.  They are IMHO mainly a toy for the CB
radio market.  Radios generally don't need a preamped mic unless they are
DESIGNED to require a preamped mic.  However, the preamp in the TUG stands is
actually an impedance matching buffer with some gain (OK, a LOT of gain) and
serves to match the mic element impedance to low impedance radios.  In every
D104 I have used, I've disconnected the amp and run without it.  I have the
same feelings about some of the FET preamp designs on the 'net.  If you
absolutely need one to match your radio impedance, fine.  But I would try
just the non-preamped mic with a 470K resistor in series first - they still
have enough output to drive a lot of rigs just fine that way, and you
eliminate an uneccesary source of potential noise, distortion, and RF
feedback.

Early versions of the TUG stands do not switch the battery off.  Current
drain is very low, but still enough to drain the battery faster than
otherwise.  This is something to be aware of if you have such a mic.  Keep a
spare battery or two around, or you will find that your mic is dead when you
really need to use it to snag that rare DX.

Check garage sales, you may get lucky and find a "Golden Eagle" version for 5
bucks like I did ... :)

Just my opinions, standard disclaimers apply....

-JIm (next project, an ElectroVoice RE20)



-- 
Jim Shorney      -->.<--Put complaints in this box
jshorney (at) inebraska.com
Ham Radio NU0C
Lincoln, NE, USA
EN10ps
http://incolor.inetnebr.com/jshorney/