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I do not possess either of these two amplifiers. Therefore there are many questions I cannot answer. All I have are the documents listed below - which are part of the documentation held by the service department at Sinclair Radionics. If you have any of the models and can supply photos, please contact me.
The System 2000 was released in the late 1960s. It underwent several changes before being renamed as the System 3000. I was involved with the design, manufacture and testing of the early System 2000 - but it was a long time ago so I have little memory of it. Other than the fact that it was built into an extruded aluminium 'box; which had end-plates glued on. The end plates rarely fitted the extrusion and there was a lot of selective assembly!
The output transistors (mounted on the rear of the amplifier) were germanium and Clive Sinclair in those days used to buy reject devices: in the early days there was a lot of trouble using these, until I built a dynamic tester which plotted the gain at high currents, showing the graph on an oscilloscope.
I do not appear to have the circuit of the very early System 2000: it had resistance wire emitter resistances joining the output transistors to the circuit board. These are not shown on the circuit diagrams I have, so I seem to be remembering a Mark Zero System 2000! Or else they simply are not shown.
Around 1970, the amplifier was totally redesigned. The redesign was available as the System 2000 Mark 2 and as the System 3000. Circuits of these were very similar! These used silicon NPN power transistors mounted on the circuit board with an internal heatsink.
I have some spare parts for these amplifiers, and can help with repairs and advise, so please contact me.