If none of the valve heaters are working it's going to be an issue with the power transformer. If it were only one or two of the valves then it might just be dead valves. I'd say book it in for service.
Agree with Crusty here. If you dont see any filament glow, or there is no B+ to the anodes then its a power supply issue and needs to be sent in for service.
I might add that the voltages (and current) involved on the B+ and B++ sides of the PS are indeed deadly, and may kill you if touched... fyi...