[DMcMahon]

Mk. 5 Update.

Checked out the modified mains wiring more. Yesterday thought that the extra on/off switch on the tone control may have been in series with the mains on/off switch on the back of the power supply, but the switches are in parallel across the switched side of the power supply switch. So either switch could switch the unit on, but both would have to be off for the unit not to be powered.

Did anybody notice the 2 yellow twisted together wires in the first photo in Post #109.

These are a ground connection, one end connecting to a ground busbar and the other end connecting to the added 6 way terminal strip connecting the screen of the 3 core mains cable and the screen of the co-ax/screened cable (inner core carrying the switched live back to the power supply), this ground/screen connection connecting back to the power supply ground/earth connection.

Because the 3 core mains cable and co-ax cable carrying the switched live are screened presumably screened cables are being used to reduce any noise/hum etc pickup at the amplifier. I have seen twisted wire connections before for ground connections, is this for common mode noise/hum reduction ? although I thought that was more for twin signal twisted pairs like differential signals.

Found that the unit was not connected to mains earth as it had a 2 round pin mains plug with the earth wire hiding inside. I will fit a new 3 core cable/3 pin plug and connect earth to the ground connection.