Quadspot GR (Quad Hi fidelity, tech pages and FAQ), not official. - Schematic, Quad 520f. A dive of Quad to Pro Audio. Excellent power amp, and a step of evolution between 405mkII
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Original Quad 22 Control Unit And Quad II Power Amplifier Instruction – Mullard Antiques and Collectibles
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QUAD 22 CONTROL UNIT 1959 SM Service Manual download, schematics, eeprom, repair info for electronics experts
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