Sometimes certain ones don't light up as much as others. But that one picture in the dark, it doesn't look like they are lit at all. You could feel them to confirm. (just the preamp tubes, power tubes or rectifier tube will burn you)
The red and purple wires at the sockets are the heater wires. Looks like they are all connected. You can swap some preamp tubes around to find out if maybe the tubes themselves are bad. Make note of where the 12AT7 belongs, but it can be swapped around for test purposes.
Once you have read up on safety for working in tube amps, you can measure those heater voltages at the tube sockets. Should be about 6VAC with one probe to red and other probe to purple.
The red and purple wires at the sockets are the heater wires. Looks like they are all connected. You can swap some preamp tubes around to find out if maybe the tubes themselves are bad. Make note of where the 12AT7 belongs, but it can be swapped around for test purposes.
Once you have read up on safety for working in tube amps, you can measure those heater voltages at the tube sockets. Should be about 6VAC with one probe to red and other probe to purple.