"Ian Bell" wrote

It also has some serious drawbacks.

1. Some god awful current spikes going up and down a longish cable
radiating crap all over the place.

There shouldn't be "god awful current spikes" unless the conduction angle is
excessively short, which isn't good for the transformer, the rectifiers or
the capacitors. Since both the a.c. conductors are, presumably, co-routed,
the magnetic fields will very largely cancel anyway.

2. AC inside a box where I am trying to keep it out by having an external
PSU

Are you using a.c. for the heaters? that has to go right up and into to the
valves, whilst the a.c. for the HT need go nowhere near them or any audio
wiring.

The reasons for keeping the transformer separate are to lose it's
weight/bulk and to remove leakage magnetic fields from the amp.

David.