In article , N_Cook wrote:
Of course the owner wants it to be as original as possible or at least
retrievable. I've convinced him that a fully bonded earth point to the
chassis is absolutely necessary for use in the UK, no getting away from
that.
Hopefully the US mains cable rubber insulation will be perished and will
need replacing anyway so would then be 3 core.
He definitely does not want the step down transformer mounted in the cab,
but external .
But if original US mains cable and US plug retained.
I'm thinking earthing coloured multistrand flexible third cable run
alongside the US cable with black heatshrink over the near-enough whole
length. The problem is what connector to use for reliable earth continuity
to the step down Tx and UK mains cable and how to make a mechanical
interlock, in effect, so the amp cannot be run without the third wire
connected.
Then what to do with the original "ground" switch ? presumably disconnect
but leave in place internally .
Do US three pin variant outlet, purpose made, step down transformers exist
in the UK, I only ever see 2 pin outlet ones. Assuming he can tolerate
swapping, but retaining with the amp, the ancient 2 pin plug.

Don't you Brits use a 110 Volt (center tapped) system for construction
site power tools? On a lot of '60s vintage transformer powered tube
gear, the only connection between either side of the power cord to chassis
ground* was a small filter cap. So the amp may be perfectly happy running
that way as neither side of the power line was expected to be ground.
And, if something goes wrong, at 60 volts or so, it should keep your
customer from killing himself.

*Ground came from somewhere else, as the gear was floating at 1/2 the
power voltage at high impedance. (Made working on transistor circuits
with an old tube 'scope a learning experience. First lesson: always
hook up the ground lead first).

Mark Zenier
Googleproofaddress(account:mzenier provider:eskimo domain:com)