Valves that glow orange are working?
Sorry to burst your bubble. In 95% of cases valves always glow orange even if they’re faulty!
So the orange glow you see is the heater. Yes a heater being a coil of wire, it has about 6.3V flowing through it causing it to glow like a vintage retro light bulb you see in a boutique coffee shop in Soho….
The heater excites electrons that flow through the vacuum inside. Even if you lose the vacuum inside the heater will probably glow…. if the plates and grids have shorted, yeah you guessed it the heater will probably glow…
It is hard to actually know if a valve is working or not by looking or feeling it, having said that power valves, the two or 4 big ones you see in the middle of the amp you may glimpse a blue wisp of plasma licking around the inside of the glass.. Yes ladies and gentlemen this is electric seen travelling through a vacuum, no wires or string or magical sorcery, simple electric current travelling it’s short lived life.
One way you can see if a valve has a damaged vacuum is when the top instead of being a mirror silver finish is like a white snowglobe or the glass looks dirty. This is bad news, it’s either developed a crack where it (the amp) has been dropped, or if it’s been stored in freezing conditions and then turned on without warming up creating thermal shock.