N3FRQ Adapter Transmitter Project

The concept is an adapter that plugs into a broadcast receiver in place of the audio output tube, which plugs into the adapter.  The resulting low-power CW transmitter draws it's power from the receiver.  The adapter is reasonably small, and can be easily concealed and transported.

The best historical information I found was in Wireless for  the Warrior - Vol 4.
I elected to design an adapter using a umbilical cord, as a one-piece unit might not fit a particular radio, or have the controls on the wrong side.

The circuits floating around (as above) are extremely rudimentary.  I don't understand how you know they are tuned and producing RF.  I also question how well they would work with an improvised antenna of arbitrary length.

An agent is playing for keeps.  He needs a better radio that this.


  • Designed for radios using octal power pentodes or beam-power tubes using the 7S or 7AC base connections, 6F6, 6V6, 50L6, etc.
  • Pi-network output, switchable for 80 and 40 meters, will match a wide range of antennas.
  • Meter indicates plate current, or RF output current.
  • 1 Watt with 120V B+ (in AC/DC set)
  • 5 Watts 300V B+ (in AC set)




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