The conversion amp between the JTM 45s and the fully lead specs amps which started in 1968. These amps still had a bass tone stack just like the 45s but mostly came equipped with EL34's (more grit) instead of the KT66 like the JTM 45 had. You can have your choice of a tube rectifier if you still want some of the classic sag of the 45s or solid state rectifier if you want a bit tighter of a sound.
When ordering solid state option
$ 2250 CAD - Hammond transformer
$ 2500 CAD - Heyboer
$ 2650 CAD - Mercury Magnetics