Welcome to MEF -
Please post a diagram or schematic so we can see what you are working on.
What do you have connected to pin 9 of the 12AX7 tubes?
What voltage are you measuring at the 100 ohm resistors when the tubes are lit?
So when the tubes go out, what is the voltage at each of the 100 ohm resistors?
And the tubes go out, do you still have your B+ voltage (to make sure you have not lost that power too) and the pilot light is on?