s2 & I put together some thoughts on how to tone tweak the sIII Normal channel.
The normal channel tone stack configuration is the original 18 Watt Tremolo Channel without the tremolo.
For less distortion:
The normal channel uses two capacitors in series (.0047 uF) off V1b 12AX7 plate with the junction of them going to a 470K bleeder (R29) then to ground . The bleeder resistor from the coupling cap to ground is R29. Replace it with a 100K or 56K.
Changing the cathode resistor by itself won't lower gain if it is bypassed by a capacitor (C16). If you lower the bypass capacitor you will filter out certain low frequencies, which will lower gain a tiny bit. Another option is to just remove the cathode bypass cap C16. Then maybe also increase the Cathode resistor R27 to 1k, 1.5K.
Bass Response: To tighten up the bass (e.g. for humbuckers) , drop the cathode cap C16 from 47uF to something like 2uF, 1uF, or .68uF
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