old Sessionette 75 Mk 2 - no output

[Mike Watterson]

.......and as a matter of interest(?) I have taken some passive tests (if any good) of the mosfets. The green mosfet values appear as 2 diodes by looks of it, does this suggest its faulty??

Almost always.

There is no need to pre-discharge gate with those testers. All capacitors should be discharged, not just Electrolytics. Very high voltage ceramic have a piezo effect so a sudden momentary short stores mechanical energy (if it was charged to 1000+ volts) and there can be a few hundred volts a little while later, so they should be left shorted longer if the discharge is a spark.