Having found the fault causing a 20V DC Offset on one channel of the 306 I bought broken, I've started to tweak and refresh/upgrade some components.
I've started by changing the main reservoir capacitors from 4,700uF to 6,800uF Nichicon Gold Tune, and the other 2 electrolytics to Nichicon too. Replaced the four marginal rated 560 ohm 4 Watt resistors to 5 Watt ultra low inductance wire wound, and the two 10 ohm 1 Watt resistors in the Zobel Network to 2 Watt 1% precision metal film (both tips very gratefully received from Light Dependent Resistor!).
More to follow!!!

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