[Diabolical Artificer]

Thanks mate, didn't think about using 2 core shielded. Anyhoo, took the coupling cap off, did as suggested, quiet as the grave, whereas before it sounded like mad Uncle Jack drilling holes with a hammer drill.

I've had this before, grounded a stage 4" away along a ground bus from previous point = oscillation, return to previous ground = all good.

Going to do a few experiments, think that coupling cap wasn't helping things. The subleties of amp building eh? Especially grounding.

Andy.