Advance monitor 15 new black indeed different from the previous series. Monitor this series using the heater voltage (tube lights) is always on even if the monitor off but still connected to PLN's power cable.
So you've Although powernya and monitor key punch die, keep the flame heater. It gives the tube to work on, like a lighted lamp kept Bolam certainly will be short lived. Eventually the tube will look dark even though the brightness and contras was 100%.
If you encounter problems like this then you should do is:
off the heater voltage of 6.3 volt power supply.
replace with 2 coil clockwise on Flyback, which one can be foot Ground and the other connects to the heater directly.
With built like this then the heater will automatically turn off if you press the power button offnya although PLN power cable still connected, so the age of the tube will be longer.
download schematic here