The schematics below come from the service manual pictured above, issued by Thomas Organ in September 1967. Besides the AC100, the other British-made amps encompassed are: the AC4, AC10, AC15, AC30 (two versions), T60, and AC50 (three versions). All the American amps are represented. There are wonderful exploded views of connectors and so on, on some of the fold-out pages.
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Cathode and fixed bias circuits
Cathode Bias - "80-100 Watt Amplifier Circuit" - dated 26th September 1963
Around 200 amplifiers were built precisely to this circuit by Westrex, serial numbers 101-300: those with the green Woden transformers. Another 130 followed built by Burndept, but with a slightly down-rated mains transformer, and a less complex output transformer: the Wodens with unpainted shrouds.
"100 Watt Amplifier" - dated 30th May 1965
Serial numbers c. 431-724. At present around fifteen amplifiers built according to this schematic are known to survive - see the 100W amplifier page for details. Others may of course come to light.
"AC 100/2 Amplifier" - dated 17th-28th June 1965 (with addition)
Note the dates: 17th June "redrawn" 28th June "Brimistor and voltages added". The addition registered on 3rd September relates to the mains transformer "T1 Voltages were 210V. Heater amps added". Perhaps this was a result of more accurate measuring. All AC100 control panels give 205V as a voltage setting. Around 1500 amplifiers were built to this schematic.
"AC 100 Amplifier" - last dated addition December 1966
Still OS/036. Supplied to Thomas Organ at some point in early 1967 and issued with the "Service Manual". There are eight notes: no. 5 records the decision to include a "Brilliant Switch", as in AC50 schematics, but as in AC50s this was never incorporated (which note 8 here states). The changes envisaged in notes 6 and 7 relate to the uprating of the power handling of a dropper resistor in the preamp (not changed in production amps), and to the layout of bias string (underchassis components in a slightly different order).
AC100 PARTS LIST - issued by Thomas Organ
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