Okay,
I was going to wait for one of the more knowledgeable folks on this site to answer your question, but if no one else is goint to tackle it, I think I can help you out.
The Sceptre and the Solarus are from the same generation of Sunn Amps. Originally based on a Dynaco stereo circuit, these amps are generally fairly clean sounding. All of the amps in this series have an S in their model name (Solarus, Sceptre, Sentura, 200s, 1200s, etc.) The first of this generation had only volume, treble and bass controls. Both the Sceptre and the Solarus have the later seven-knob layout, adding contour (mid), reverb and tremolo to the circuit. The early Solarus amps had a pair of EL-34s and put out around 40-watts. The Solarus was originally a 2x12 combo, but was later offerred in a head versiuon. The Sceptre and later Solarus had beefier transformers and were 60-watt heads with a pair of either 6550 tubes or KT-88s. There were also Sunn heads like the 1200s which featured four power tubes, a pair of rectifier tubes and 120-watts of output. All of these "s" series heads were electronicall similar and in some cases, like the Sceptre and the Sentura II, identical. Sunn sold these two heads with different cabinets, however, and thus the two different names.
The Model-T is a different beast. While its power section is similar to the earlier Sunn heads, its preamp section is more complex, supposedly borrowing from the Marshalls of the same period. It may be that Sunn's experience providing amplifiers to Pete Townsend and Jimi Hendrix pushed toward a more Marshall-like sound.
I hope this helps. You will find schematics for all of these amps on this site.
-Blownaparte
