Question about tubes in the old days

Many tube amps did not have adjustable bias voltage. The tubes were "self biased". This means less power amd/or more distortion, but it did mean a lot less fussy work.
Tubes seemed to last forever. I once had a Heathkit amp where the output tubes pulsated with a blue glow in time with the music, but I didn't replace the tubes. It was cool.

When I was in high school (70's) I had a Dynaco SCA-35 integrated amp...about 17 watts/side using EL-84 tubes. I listened to that thing for hours on end. I never replaced a tube. When I went to college I moved to a Pioneer solid state receiver. Fast forward many years....I figure that tubes are pretty cool again. I go home and find that old integrated amp stashed away. I plug it in. Wonderful sound from all the original tubes. My experience would suggest that old gear and old European tubes lasted a long time.