chiming in late and maybe not seeing everything........ if using fast PSU, independent ones for main and biasing
one of solutions is - biasing PSU directly powered by mains switch, also powering adequate relay (with or without simple RC delay cell) and that relay powering main switching PSU
that way biasing mech. made strictly safe for SIT, and arrangement ensuring that main rail is powered only if biasing voltage is present
one of solutions is - biasing PSU directly powered by mains switch, also powering adequate relay (with or without simple RC delay cell) and that relay powering main switching PSU
that way biasing mech. made strictly safe for SIT, and arrangement ensuring that main rail is powered only if biasing voltage is present