Waking up an old Tektronix

[MIPS]

I recently came into ownership of a Tektronix 535 oscilloscope and a few neat plugins however that I can tell it has not seen use for a number of decades.

I have it somewhat dismantled right now as I do some repairs and inspect the stacked capacitors but I'm trying to figure out how to wake the chassis up. Under normal circumstances there is a delay relay that lets the tubes light and voltages stabilize before bringing the rest of the chassis up. I am not sure if I can safely variac the system in this state. Does anyone have suggestions?