taken from DTB
Galaxy 33-88, Connex 3300, and similar units:
"Supertune": Change R174 and 187 from 10k units to 2.2k units. Peak L31, L33, L40, L42, L43, L44, L51, and L52 for best swing, using a loud, steady "aaaah" sound in the mic. Set carrier control pots as normal for high and low power levels. For louder, cleaner talkback, solder a .1uf capacitor in series with a resistor (5k on up) from pin 4 of the audio chip to J25 (small wire jumper in front of TR32 on parts side of board, near the mic socket). If you use a resistor higher than 10k, you can skip the capacitor, unless you desire a higher tone for the talkback. Experiment a bit for best resuslts. If desired, you can replace R238 with a rectifier diode, with its banded end pointed towards the mic-jack side of the radio. NOTE: this can increase the possibility of feedback in hot operating conditions, but adds alot of room in the modulation for lower-output mics like the Astatic 636L. If feedback occurs after warm-up, nake sure the AM regulator is securely mounted and completely FLUSH against the chassis.
AMC Mod: Change C133 (center of the board, about 2-2.5 inches from back edge, next to TR 34) from 10uf to 4.7 uf. This makes the AMC action much snappier, and gives better average loudness.