Quote:
Originally Posted by Synchrodyne
Middle tone controls generally seemed to have been seldom used. Perhaps the most notable user was Tripletone, which company name (changed from the original Servio) was derived from the fact that its first amplifier, the Mk I of 1954, had three tone controls, treble, middle and bass. This feature was retained, as far as I know, on all subsequent Tripletone amplifiers, both valve and solid-state. Whether Tripletone used passive or active tone control circuitry is unknown; schematics for its equipment appear to be unobtanium. Active circuits were gaining ground by 1954, so that approach was certainly possible. On the other hand, valve count constraints in simple amplifiers may have pointed to the passive type.
Cheers,
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A friend of mine owned a Tripletone 10W amplifier in the late 1950s. The main unusual feature that I remember was that turning bass, middle and treble to minimum had much the same effect as turning down the volume to zero. That suggested three separate filters whose outputs were mixed together. They were probably passive filters because the valve complement was pretty standard.
Unfortunately I never had the opportunity to investigate the circuit.
Martin