Tue May 10 12:30:24 EDT 1994

Well, baseball season has started and Field Day discussion has been
steadily increasing on the reflector, so I think its time for me to ask:

"How do you trouble shoot traps on a TH-3?"

"How do you trouble shoot traps on a TA-33?"

I seem to be the custodian of a couple of these things and since the
TH-3 acted as a rotatable dummy load last year at FD, I thought I would
try to bring it back into serviceable condition.

I know that its not really in the spirit of FD to plan ahead, but I will
not tolerate another 24 hrs of 10 rate on the high bands.

I have sweep gens and analyzers available if need be.

I hope most of the responces will say something like:
        "Pull the traps apart and clean the spiders out and they
         will work super"

I hope.

Eric, NV6O
Consumnes River Phased Vertical and Barbeque Society
edwoods at

>From Edward Parish <parish at Think.COM>  Tue May 10 20:10:27 1994
From: Edward Parish <parish at Think.COM> (Edward Parish)
Date: Tue, 10 May 94 15:10:27 EDT
Subject: Heil Pro-Set
Message-ID: <9405101910.AA04364 at>

I talked briefly with Heil at Dayton about the Pro-Set.  Since I have da no
problems with it, I told them that I was a satisfied customer.  He gave me
a handout about the common problems and solutions and asked me to post it
to the net.  I have OCR'd it, but not proof read it.  It gets a bit hairy
once you get to the hand drawn schematics (they don't come out and I am not
about to ascii draw them).  I can get a postscript version of this if
someone *really* wants it.

                             HELPFUL HINTS FOR THE PRO-SET


The HEIL PRO-SET has the headphones wired into a standard l/4" STEREO
3-conductor plug.  This allows the use of the PRO-SET with dual diversity
receivers such as the Yaseu FT-1000.  Most other monaural receivers have a 3
conductor stereo jack wired to feed the mono signal into both headphone
speakers.  Simply plugging the l/4" stereo plug all the way into the front
panel 'headphone' jack will feed audio to BOTH sides.  Should that not be
the condition, you will want to use a l/4" mono/stereo adapter. These are
easily available at Radio Shack and other electronic supply stores.  You
also have the option of cutting the stereo plug from the PRO-SET cable and
soldering a mono 2 conductor jack to the cable, thus foregoing any adapters.
You NOT be able to use the PRO-SET in a stereo mode, however.

The earpads are removable for washing or replacing.  The pads are
stretched onto a plastic 'ring' assembly that snaps onto the main body of
the PRO-SET.  Carefully pry that ring away from the headphone assembly and
remove the ear cushion.  This also exposes three small Phillips head screws
that hold the speaker plate onto the main body.  Removing those three
screws will gain easy access to the speakers and cabling should you every
have any problems.  With heavy use, there can be a condition where the
cable becomes intermittent - just as it enters the headphone speaker shell
housing.  Removing the speaker plate gains the access to pull that cable up
into the housing and cutting off the broken spot, resoldering the new


The microphone boom of the PRO-SET is shipped one of two ways.  Either with
the HC-5 full range Key Element or the HC-4 'DX Dream Machine' which rolls
off the last octave of bass response and puts a 10 dB peak at 2,000 Hz.
right in the middle of the human voice range which creates an extremely
crisp and articulate audio signal through a SSB filter network.  There is
either a blue HC-5 or red HC-4 sticker on the swivel point of the
microphone boom arm which tells you which element has been installed into
your PRO-SET.

Since 1982, the Key Element has been the choice of the top DX and Contest
operations throughout the world.  It was designed to work into the low
impedance inputs of all amateur radio transceivers.  It does not work into
the older high impedance inputs as found in tube type equipment.  A
matching transformer would be necessary to properly match the impedance.

Proper use of ANY communications microphone elements should be extremely
close talked.  Can it fit in the back of your throat?  Great!  Reason for
this is that in communications situations, very seldom is the operating
position in a perfect acoustic situation like found in a recording studio,
etc.  With reverberant walls, windows, etc. the audio reflects like crazy
thus, to set only your voice into that microphone and NOT the amplifier's
blower, the riV set or cars roaring by, the microphone gain should be
reduced to a minimum and the microphone should NEVER be more than l/2 inch
away frorn your mouth.  NEVER!

It was for this reason Bob Heil designed his fcmos Key Element 10 dB lower
in gain than most microphones.  This will force the operator to close talk
the Key, Element, adjust the microphone gain to it's correct input level and
rid the airwaves of blower and street noises.  All that is left is crisp,
clear articulate speech audio - the tradennark of a Heil microphone

As with any great theory, this works extremely well but there are a few
transceivers that have a few problems working in the perfect world.  Kenwood
and Yaesu have no problems and when matched with the Heil Key Element,
produce superb speech audio.  The Icom series of transceivers sometimes
create some problems for the user.  Icom has designed their microphone
pre-amp section about 10 dB Low in gain as they continue to supply a
microphone with a pre-amp built- in.  These microphones use a very
inexpensive .E.T. cartridge that was designed for P.A.  use and is simply
too mushy and bassy for SSB suppressed carrier operation.  When trying to
interface with the extremely articulate HEIL Key Element the operator will
have to turn the microphone gain to its maximum position.  No problem with
this.  It becc,mes a psychological problem more than electronic in that the
operator , for years has used paging and entertainment microphones which
have way too much gain and thus forced to use the microphone gain just
barely cracked open.  With all that gain, we have suffered blower and room
noise only to blame it on the compressors.  How terrible!  The problem is
that, by habit over the years, the mic gain is set at a very Low level.  NOW
you will have to increase that by a considerable amount because the HEIL
Key Element now producing the CORRECT gain structure needs the pre
amplifier to be increase a bit and when you do, your sigrlal will be VERY
clean, crisp and articulate.  No more bassy, mushy SSB siynals.

There are occasions,  however  that some of the ICOM microphone pre anplifler
sections do NOT have enough gain - even when set wide open - to produce 
transmitter output.  There is a simple fix for that condition.  Simply increase
the value of the feedback resistor by 150K ohm or so, and that ICOM will come
alive!  They make it very easy to do as most of their equipment is built use the
vertical component mounting and so you don't even have to get under the p.c.
board and most of them can be done in a few minutes by simply lifting their tops.


In addition to this -ldB gain problem with their microphone pre-amp
section, there is +8 volts D.C. srrimosed oo the audio lirle which is used
power their 'CB' type base microphones.  Tlle HEIL Key Element cartridges
are bobbin wound dynamic elements and MUST be decoupled.  en the blue ICOM
AD-l adapter or the HM-10 microphones are built, the Hell are automatically
installs a .47 mfd.  capacitor in series with the ICOM audio lead to
correct that problem.

To increase the microphone pre-cnplifer gain to the correct level, you will have
to increase the feedback resistor of the pre amp.  Here's an example of a few of
the  ICM  models.    Check  your  service  manual  to make  certain  your model
corresponds to the right resistor and its value.  You also will be able to find
the exact location .
                                  Hre are the factory values of the feedkack (FCB) resistcrs
                                  By inserting a 150K - 220K in sories with
                                  FDB fcr gain increase

                           IC781 R308 56K
                           IC735 R235 l00K
                           IC765 R305 82K
                           IC751 R264 82K

You will also discover that the audio ground and DC grounds are NOT at the
same potential.  Open the 8 pin Foster plug and jurnp pins 6 and 7 together
ana bring the end of that lead out of the connector housing. As you
reassemble the housing, connect that jumper to one of the small phillips
head screws holding the cable clamp.  You have then grounded the adio
ground, PTT ground and the chassis ground to one potential.  It solves MANY
RFI and audio feedback problenns that ICOM equiprnent are amos for.

A wonderful transceiver built back in the early 80's was the ICOM IC-740.
The big problem is that it had to be used with a pre-amplified microphone.
With a simple cut f a resistor, the gain can be restored to a normal level
to be used with the HEIL Key Element.  While at it clip R-81 to remove the
D.C. voltage that is superimposed on the audio line.

The principles involved in this modification can be applied to other ICOM
models as well.  .  F '7

        I IC Pl r     r  , .t .

         t I ! 

Should you have an older tube transmitter that requires a pre-amplifier,
here's a simple circuit that can be built by those who are adept with a
soldering iron.  Thanks to John Silva, N3AM for sharing his circuit used
with a Drake TR-7.
                              70            \r

                          J             1 1       ! J T

             '' T .s i i 

                         ,         r-


>From sellington" <sellington at  Tue May 10 15:13:03 1994
From: sellington" <sellington at (sellington)
Date: 10 May 94 14:13:03 U
Subject: low rhombic as rcv ant

I'm not sure, but I don't believe it will work any better than a single-wire
terminated Beverage.  As I recall, a wire close to the ground radiates (and
receives) vertically polarized signals off the ends, while a wire far
from the ground radiates at an angle close to the wire.

Scott  K9MA

>From sellington" <sellington at  Tue May 10 15:19:01 1994
From: sellington" <sellington at (sellington)
Date: 10 May 94 14:19:01 U
Message-ID: <9405101919.AA07366 at ns.PacBell.COM>

You can test traps (off the antenna) with a dip meter by coupling to the
short tube at each end of the trap.  You should see a nice sharp dip close
to the appropriate band.  And, of course, the traps from opposite sides 
should dip at the same frequency.  If the traps are good, and you put it
together right, the antenna should work, right?

Scott  K9MA

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