Good news! Only one of the tubes does not light.
This means that at least some of the other stuff is working.
You say 19J6, so I'm guessing that you have built this schematic:-
It sounds like you have already tried most sensible possibilities, now we have to look for less likely possibilities.
Check that you actually have ~19V on pin 3 of the tube that doesn't light. Not 'at pin 3 of the tube socket', but actually on the pin. Most sockets will still let you access the pin from the bottom, or you'll have to try to get by pulling the tube partway out of the socket. On occasion corrosion can prevent a good contact.
Check for continuity between pin 4 (of the tube) and ground.
Check for continuity between pins 3 and 4 of the affected tube. 19V/150mA, you should have a resistance of ~123 ohms.
If you have these things, the tube will light.
Now - you can have ~19V showing at pin 3, and there still be a fault, if there is no continuity to ground (the tube is open circuit or pin 4 is not making good contact to ground), if there is a poor joint somewhere further up towards the PSU. This will result in there being ~19V measured (through a high impedance), but it will collapse when a good ground is made, so you need to be sure that the 19V is there when the tube is not O/C and pin 4 is securely grounded.