Simple Speech Amp Mod

Although I have labeled this the KG2IC mod, I am by no means the originator, rather it is a collection of information that I have collated from various sources.

The following simple mod will produce quite good audio from the stock T-368. This mod retains the use of the stock speech amp, and easily reversible if needed. All that you need is a soldering iron, solder, and some jumper wire.

Get your soldering iron ready!

  • Power down the T-368, remove the line cord from the wall.
  • Remove the modulator deck from the chassis.
  • We will be working only with the speech amp for this mod. Remove the speech amp, located in the left rear area of the modulator deck.
  • Remove the tube shield from the 5726 clipper tube. It is located near the center of the speech amp chassis.
  • Remove the 5726 tube from it’s socket.
  • Jumper pins 1 & 5 of the 5726 tube socket, this bypasses the clipper circuit. The easy way to do this is by pushing a heavy paperclip into the tube socket pins. Leave the 5726 tube out, but reinstall the tube shield.
  • Now locate filters FL1 and FL2 on the speech amp chassis. They are located near the ends of the unit.
  • Bypass FL1 and FL2. Simply tie the green and yellow wires together (your colors may vary). Some of the later speech amp filter terminals are labeled “in” and “out”, the wires going to these terminals are the ones to connect together. Be certain to remove the ground wire from the filters.
  • To avoid the possibility of hum pickup, install a terminated BNC connector on the unused speech amp audio input.
  • Reinstall the speech amp onto the modulator deck.
  • Reinstall the modulator deck in the main chassis.
  • For future reference, document the mod somewhere in your notebook.
  • Power up the unit and enjoy!

Results

Transmit audio response will now be almost flat from 200-20,000 cycles per second. The Astatic D-104 sounds quite good with this mod. If you wish to modify the audio response, an external audio processing unit or equalizer may be used.

If you really have to have near broadcast quality audio a better, abet more complicated, mod is the N9FOY detailed on the main T-368 page.