Hum problem on a valve amp

Actually a Velleman K4000 kit stereo valve amp from 1994.
Not just hum but mains noise, eg dimmer spike noise.
It would seem to not have a proper grounding point.
Specially thickened ground lines on the ps board, large ground interconnects
to the preamp and main amp 0V lines and input sockets insulated isolated
from chassis which is bonded to the 3 wire mains input at the IEC socket.
The kit construction literature makes no reference to connecting the
thickened ps ground lines to the mains bond point and seemingly relying on
earthing of whatever is used as a non-integrated preamp or external source.
What is the point of reinforced ps ground tracks if they conduct current
nowhere , only via signal line braid, so a safety issue as well
Surely there should be a heavy strap between the ps ground and the mains
ground point ? I only have the amp for attention which is line level input
to speaker output so no volume or tone controls.