Icom IC-736

Settable CW sidetone

This looks as another "feature" that should discourage real CW OPs from purchasing IC-736 (in order they purchase more expensive IC-775). The level of the CW sidetone can only be set by a trimmer on the MAIN board. To make it perfect the board is mounted in the up side down way. This means you must remove both covers and turn the whole TCVR up side down to reach the trimmer.

Modification part 1

As there was some little space left on the rear panel I decided to place a small potentiometer there.

I purchased a tiny potentiometer 1K (linear) and made a small interfacing PCB.
I drilled a hole in the rear panel for the potentiometer.
To make it clear for the next generations I made a label for it (self-adhesive lamino).
I located R264 on the MAIN board and mapped its pins to the schematics.
I removed R264 from the MAIN board and replaced with two tiny shielded wires. These are terminated with a connector. The connector is pushed on the interfacing board (see the top right corner).
Finally, I found a suitable knob for the potentiometer in the junk box.

Modification part 2

Having done the Part 1 it is possible to set the level of the CW sidetone. It is however still dependent on the AF volume knob. This is not much convenient as it is usual that you manipulate AF volume rather often. For example you increase volume when digging an extremely thin station from a noise. Having done the difficult QSO you again turn AF volume back to normal to save your precious ears. It is better when level of the CW sidetone doesn't change with AF volume.

Locate condenser C294 and remove it. This will discontinue the path to Q112. Q112 is the an emitter follower right in front of the AF volume potentiometer. You won't here any sidetone from now.
The new path will lead from the middle pin of the new CW sidetone level potentiometer to the pin 1 of the final AF stage uPC1241H. To separate potentials and reduce level use a condenser 100N in series with 100K rezistor.

Having done the Part 2 it is possible to adjust CW sidetone level with the potentiometer on the rear panel independently on any other control.


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