Some idea of the development history of treble-and-bass form of tone control may be gleaned from the attached exchange between P.J. Walker and D.T.N. Williamson in the letters pages of WW 1949 December:
The Williamson circuit to which the comments referred was this one:
One has the impression that PJW had put some work into what presumably was the tone control for the QA12/P in an effort to get the right curve shapes and not just single-knob control for each of the treble and bass. An interesting comment he made was:
‘Tone control should be applied with the greatest discretion, but a small amount of “compensation” correctly shaped can on occasions prove beneficial”.’ I’d say that the tilt control on the Quad 44 et al is a model of discretion.
Cheers,