Digital tone controls
Not much yet, just the idea: each tone control (bass and treble) consists of two tubes operating in antiparallel, that is: 180° out of phase. Their outputs are added:
(0° bass) + (180° bass) + (0° treble) + (180° treble) + (original signal) = output
Because tubes distort terribly near cutoff, each operates in a region inbetween cutoff and fully on (near grid current). For 0% bass/treble, the out-of-phase signals cancel out. This will yield acceptable distortion.
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