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Sinclair Radionics - System 2000 and System 3000 amplifiers

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 redesigned as the System 2000 Mk2 and an up-market version released - 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. In the early days the end plates rarely fitted the extrusion and there was a lot of selective assembly! And a lot of rejects!

The early System 2000 Amplifier

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! However the circuit of the Mk1a is available. There was also a Mk1b - which had R34 L and R added to pre-charge the input capacitors to remove switching noise when an input was changed.

The later System 2000 and 3000 Amplifiers

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.

• Circuit diagram, 2000 Mark 1 is not available.
• Circuit diagram, 2000 Mark 1A
• Front panel of Mk1 2000, showing push button input combinations
• Circuit diagram, 2000 Mark 1B These both show phono socket inputs, but they used DIN sockets. There are photos of the early Mark 1 at Retrokit
  The only difference between Mk1 1A and Mk1B is R34. This was across the treble control. It was removed in 1B. A resistor was added in 1B at the input to charge C1. The appellation R34 was re-used. Some values had been changed during the life of the Mk1A - these are shown on the Mk1A circuit diagram, the later values being in blue.
• Photo of inside of a late Mk1B
• Photo of front of a late Mk1B
• The above two photos are part of a gallery of photos of a late Mk1B Sinclair 2000 amplifier and a Sinclair 3000 amplifier.
• Circuit diagram, 2000 Mark 2
  This circuit was re-drawn from an original data sheet I possess. The main visible differences between the Mark 1 and Mark 2 was that the Mk2 has PCB mounted 3 or 5 pin DIN sockets, The Mk 1 used chassis-mounted DIN sockets on the rear of the amplifier. The Mk1 also had the power transistors (TO3 devices) mounted on the back of the chassis whereas the Mk 2 had these internally, mounted on the PCB. There were of course significant difference in the internal circuitry.
• Circuit diagram, 3000 Amplifier The 3000 and later 2000 amplifiers were essentially the same circuit but with additions in the 300. So this is the 2000 circuit above updated with the extras present in the 3000 with help from an owner of a System 3000 amplifier.
• Differences between 2000 Mark 2 and 3000
• Scans of original Sinclair data sheets of copper PCB and component layouts of 2000 and 3000 amplifiers
• Scans of various Sinclair Technical Information sheets, giving transistor types, service information etc.

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