 In 1963, the single tone control was replaced with individual bass and treble control knobs, and the base Princeton was joined by the Princeton Reverb.A pull-out "boost" switch was added to the volume pot in 1978.The Princeton is particularly famous as the basis for Mesa Boogie's Mark I, which is a heavily hotrodded Princeton equipped with modified preamp and a Bassman transformer, allowing it a higher gain output of 60 watts.