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HOMEBREW HI-FI AM DRIVER TRANSMITTER

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I always wanted to build a simple 160-10 meter AM driver transmitter.  Over the years I have built/gathered a remote variable power supply, a hi-fi modulator and an digital RF generator that made this project very easy.

Here it is, 10" long x 9" wide  x 6" high and weighs 5 pounds.  I call it a driver transmitter because I chose the linear amplifier route to high power AM, so I run this driver at 8 watts of carrier.   By increasing the power supply variac and adjusting the modulator one could run 50 watts of AM carrier with hi-fi audio.

                   

 

SCHEMATIC AND BLOCK DIAGRAM:

    

CONFIGURATION:  The IC-718 drives 10 watts into a T-connector with a dummy load on one side and the un-tuned grid of the 6146 on the other side.  (The 6146 grid wants voltage; however the 10 watt driver into the 50 ohm dummy load provides  enough voltage to do the job.  It does waste power, but it was easy and it works).

 

EXISTING POWER SUPPLY:

1.  Bread board 22" x 22" x 3/4".
2.  Variac for the high voltage plate supply and screen supply.  (Another power supply is
     on the same board, from another project).
3.  Push to Talk control relays to switch 6146 plate B+, screen and 120 VAC for the 
     external antenna relay.

    

 

EXISTING MODULATOR:

1.  Hammond 1642SE mod transformer, 75 watts, 20-20kHz between the 6146 and B+.
     (modulator capable of modulating a 110 watt carrier).
2.  8 ohm audio power amplifier to the mod transformer input.
3.  The homebrew 6146 driver is flat from 20 Hz to 5 kHz; the DEQ2496 digital processor
     is just used for a compressor-limiter function.

              

 

CONSTRUCTION:

1.  The pi-network was part of a DX-60.  It was modified to work at 160 meters and I
     eliminated the 15 meter position.
2.  The 6146 grid is un-tuned.  This freed up the wafer switch that used to switch the
     buffer tank circuit.  This wafer now  switches in pi input caps for both 160 and 80.
3.  The chassis was hack sawed down from a much larger DX-60 chassis.

 

CONCLUSION and SIZE COMPARISON:  I ran all the tests into the dummy load and the transmitter makes hi-fi audio from 1 watt to 50 watts of carrier.  The homebrew rig now replaces the Viking II.



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