the auto bias protection fuse circuit works great; sure, the red led lights up for the bad tube; pretty easy to see when a kt120 archs and the system shuts down...the quick blow fuses saved the auto bias board from any damage; simply replaced the two fuses and i was back in business...well, except for a new kt120 tube...but in any case, Prima Luna has an old school look, no bells and whistles...all the good stuff is under the hood but shows up nicely in one's ears....they have went up about $1500 or so since 2020 when i bought my first evo400 tube amp; just got a 2nd evo400 tube amp so i can go dual mono; running all kt120s and sound is different than stock/oem tubes...and better BUT ONLY because it's a slightly different sound..the origial tubes EL34's are perfect as is...but tube rolling, while it can get expensive ($125 a tube x 8) is ok...but i'm not that much of a gear head...i think i just liked the look of a bigger tube, and more orange glow....however, I am not going to the KT150s as there plates sort of hide the tube glow......all that being said; the value of primaluna gear is superb....sure, it's not pretty as McIntosh or high-end like ARC and D'Agostino ...but you'll have several tens of thousands of dollars in savings...and your ears will never know the difference.....peace of mind/piece of mind...