[AMRadio] (no subject)

John Coleman ARS WA5BXO wa5bxo2005 at pctechref.com
Sun Jul 31 17:55:08 EDT 2005

I have been asked a lot about the rig so I will send this out to the




Movies and audio below provided below by W5OMR




Your Welcome Herb


            The main AM rig is spread out into two rooms.  It is mostly
home brew and a lot of modifications.  Even the scope is homebrew.  The
XMTR room that holds the 6FT rack cabinet is adjacent to the operations
console.  The 6Ft rack now holds the final amplifier which is a home
brewed class C push pull pair of 250ths with link coupling input and
output.  Just below the Final chassis is the high level modulator
chassis which is four 813s in push pull parallel class AB1.  The power
supplies for these are built in the back side and bottom of the rack
cabinet.  The modulator supply is 2500 Volts with its own plate XFMR and
filters.  The final supply is a separate supply with its own plate XFMR
and filters but the primary of the plate XFMR for it is passing through
a Variac, so that I can adjust the plate supply voltage on the final
amp.  I generally run about 1600 volts and some where between 300 to 400
milliamps of plate current. 

	In the operations console of the other room is the HQ-145 RCVR
and various other pieces of equipment.  Most of the Equipment can be
patched around in such a way that any of it can be used for carrier
excitation to the AM big rig in the other room. Each piece can be
operated in stand alone also. 

            When on AM at 3885mhz, this is this is the general setup.

            The carrier generation begins with a modified TS820 putting
out a carrier at about 10-20 watts.  This goes into a Heath kit modified
SB200 amplifier that brings this up to a 75 watt carrier.  This then
drives the big rig (PP 250ths) which puts out about 350 watts of

            The audio chain begins with a home brewed microphone built
into and old Shure dynamic microphone housing.  You may notice the 4 red
LEDs inside the microphone.  The output of the microphone feeds a Shure
mixer with auto output leveling.  The mixer feeds the main speech
amplifier which is a much modified Bogen PA amplifier.  The Bogen PA amp
feeds the grids of the big modulator in the other room.  The big
modulator with the four 813s is capable of 1200 watts of audio but now
days we only need about 200 watt from it so it sort of loafs along.  The
out put of the big modulator is feed to a 40 HENRY choke which K4KYV and
I sort of built from 2 chokes, in series with the plate supply to final
Class C carrier amplifier so that the audio can be imposed on the 1600
volt DC that is feeding the plate circuit of the 250th's.  There is
enough audio reserve to over modulate by 300 percent so you see the need
for the Shure auto output leveling mixer.   

            The out put of the big rig is feed into a home brewed
balanced tuner that is mounted on the wall above the operations console.
The 600 ohm balanced feed line from the antenna comes through a small
Plexiglas window in the wall behind the tuner.  The antenna and balanced
feed line is made from number 12 wire.  There is about 120 feet of the
balanced feed line going up to the center of the dipole antenna which is
just less than 100 ft high.  There is about 125 ft of wire making up
each leg of the antenna for a total antenna length of 250 ft. The ends
of the ant are about 70 ft high.

            This type of setup is not your every day rig but is an
accumulation of stuff over many years and my good friend BJ and I make
it continue to evolve. 

Good Luck



-----Original Message-----
From: Herb Raemsch [mailto:hwr79 at chilitech.net] 
Sent: Sunday, July 31, 2005 2:34 PM
To: wa5bxo at qsl.net
Subject: Speaker Suggestions

    Hello John

   Thank You very much for the suggestions on the speaker. Appreciate it
very much. Boy that is anice looking transmitter pictured on QRZ
web-site. Was wandering what make and model.

   Anyways I appreciate your input very much. I have been on SSB to long
and have forgotten a lot. At 64 am going back to CW and AM so its guys
like you I lean toward for a little help.

                                                            Thank You

                                                          Herb WA3HGT

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