Problem with AR Ref 300 Mk II - any experience?

One of my Audio Research Ref 300 Mk II Power Amps has no output. Power ist ok, Switch on process is as usual, but the 8 power valves show practically no voltage when checked. The meter moves only some 3mm from the "parking position" on the left side.
Does anyone have any similar experience?
Are there any switches, additional fuses or the like, which I am not aware of?
Best regards!
Otto