[DonaldStott]

Ah, well spotted Lawrence - it was a typo and my picture in Post 42 above clearly shows the connection to Pin 8 of the CY31, the Cathode.

Any idea why someone would install a tubular capacitor from the IEC sockets mains earth tag?

There is also still the mystery of the –ve ends of C27 and C29 which are connected to the enclosure (is that the right word) of the on/off switch/volume control – this connection is not shown on the circuit diagram??