The part numbers apply to the 148 GTL. Other units may have different part numbers. If you suspect that, compare schematics before proceeding.
1. Remove R44, D52, and R149.
2. Trace the wires from the clarifier control to where they enter the main board.
3. One of the wires goes to ground through R175. Cut that wire right at the board and solder it to any nearby tuning can (chassis ground). Scrape the plating off of the area of the can you intend to solder the wire to.
4. Another of the wires that arrives at the plug has a trace leading to R174.
Cut that wire at the board. Strip and tin 1/8" of it and solder it into the
empty D52 hole that is closest to L27.
5. Cut the last wire that arrives at the board. Lengthen it and solder it
to pin 1 on IC4 (the 8-pin voltage regulator IC that is fastened to chassis
rail ahead of the AM regulator and audio IC).
6. To finish the job you'll need a frequency counter and an audio signal
generator or SSB monitor radio that is known to be on frequency.
7. Center the clarifier control and transmit an unmodulated carrier on AM.
Use L23 and the frequency counter to put the radio on frequency.
8. Set up the audio signal generator to output a 50 mV, 1000 cycle signal.
Pipe that signal into the mic socket. Put the radio in the USB mode, key the
mic and set the mic gain so that the radio outputs a big enough signal to
make the frequency counter indicate. Adjust L59 to put the radio on frequency.
Remember to add the 1000 cycle offset. Example: On Channel 20 the frequency
should be 27.206000 (The carrier frequency of 27.205 plus the 1000 cycle audio signal).
9. Switch to LSB and use L22 to put the radio on frequency.
Remember to subtract the 1000 cycle offset (Channel 20 frequency = 27.204000).
10. An alternative to steps 8 and 9 is to use a sideband monitor receiver.
Set up the monitor receiver so that it can hear the radio that you are working on.
Make sure the monitor is on center frequency and the modes (LSB or USB) match.
Use L59 to make the USB signal sound natural, and L22 to make LSB sound natural
when listening to yourself on the monitor receiver.
Note: when done correctly this mod should result in roughly 11kHz of downslide (enough to shift to the next lower channel with a little to spare), 6 kHz of upslide (enough to go in between channels with a little to spare), and a centered control when on-frequency operation is desired. The control will be touchy and will take some getting used to.
If you have any questions, feel free to e-mail me.
Good luck and have fun.
Bill Eitner (1-1-02 and 4-16-03)