I've used JJs (not 88s however, mostly El84s and 6V6s) in guitar amps for years and they're great.
Jedinite24...my 502 bias LEDs vary mightily depending on what time of day it is and what is going on in my house (laundry, dishwasher). None of my tubes drift much but those LEDs have become something of an "available juice" sensor, even though none of my tubes are dying yet. I check things with a meter just to be sure and it's never changed more than a tiny fraction and always well within the Jolida recomended range, regardless of tube type.
Jedinite24...my 502 bias LEDs vary mightily depending on what time of day it is and what is going on in my house (laundry, dishwasher). None of my tubes drift much but those LEDs have become something of an "available juice" sensor, even though none of my tubes are dying yet. I check things with a meter just to be sure and it's never changed more than a tiny fraction and always well within the Jolida recomended range, regardless of tube type.