My brother dropped this 36+-year-old british hi-fi amp in for service because it was mainly outputting hum. I changed the capacitors in the power supply and power amplifier to get it back up and running, and checked to see if the factory spec was a marketing department fabrication.

Props to Jim Lesurf for providing lots of useful information about these amps: http://www.audiomisc.co.uk/Armstrong/armstrong.html

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Edit: list of the part numbers I used for replacements:

Reservoir cap (486?) was 7500uF 90V (schematic says 3300uF?!) now 8200uF 100V

DC blocking caps (481, one per channel) was 4000uF now 4700uF 100V

On the A17 amplifier board (all in pairs, one per channel):

479 was 50uF now 47uF 63V Farnell 1165612

478 was 100uF now 100uF 63V Farnell 1165613

473 was 10uF now 10uF 100V Farnell 2342136

474 was 200uF now 220uF 100V Farnell 1165480

472 was 47uF now 47uF 100V Farnell 1165565