You simply can not light up a tube with 9 volts, can't be done. The tube is working and coloring the tone but it just won't light up. There are actually three ways you can use a tube in a pedal and I personally don't like the tone of any of them. The LEDs are purely cosmetic.
Some preamp tubes don't light up even in amps... mine don't. They're lit but the filament is encased so you can't see the light

Thank god for Engl and their LEDs.