Tube Life: power vs. preamp

I know this is a highly subjective question, but here goes.... I have a Fender Custom Vibrolux which I love. I play it at low volumes (3 to 4 1/2) approximately 6 hours per week. It is approximatley a year old, with the factory tubes. I believe Fender sets the voltage gojng to the preamp tubes fairly high to increase the gain and make this amp break up more easily. At this rate, approximately how long should the preamp tubes last before there is a noticeable degradation in performance? (yes, I have a pretty good ear for tone). How about the 6L6's ? (assuming the tubes don't go microphonic)

Pre-amp tubes can last a Loooooong time. 10 years sometimes....maybe more

Depending on the amp, power tubes can last anywhere from 6 months to a couple of years. My TE Velocette munches EL84s but then again, I only play with it on 10. My '65 BFDR goes a few years without new tubes.

I have a pair of Mullard (Vox Label) 12AX7s that still sound good after 38 years. :D

My Dad used to say don't go opening a can of worms unless you intend to go fishing for trouble, but here goes. The 'old stuff' was biased to what many modern 'gurus' consider cold, and today we tend to like the tone of 6L6's biased hotter. I'm sure many of us have seen an old Fender or two along our journeys with the original tubes. When I found my Blonde Bassman head a while back, it had the original tubes. The amplifier still sounded killer, and the tubes tested very strong. There is no adjustable bias in this 6G6B, and when I checked the bias it was sitting at a chilly 25mA per tube. Today, you have a hard time getting tubes to last that long because it is a habit to bias hotter.
Well, there's the can of worms. I would check your tubes, and write doen any test results. Check 'em again in six months. If the numbers drop dramatically, change the tubes. Check the bias, and make a note. If it came from the factory 'cold', the tubes should last a while yet. I know the old reissue Bassman combos came out of the gate 'cold', but that is a horse of a different color. The bias wasn't why that amp didn't sound too good 'stock'. If you like your tone now, make notes of what is going on inside. That makes it easier to replicate that tone when you do change tubes.

I got some tubes 40 year old. Still test new, sound great. Both power and preamp. Some tubes like 12AT7s in preamps go quickly.

Others can last literally forever. I'd never throw old functioning ones out, unless known microphonic, or test as having a gas leak.

Good info. Thank you.

Most of the tubes in my 1965 Deluxe Reverb are the original ones from the 1960s and still work great. New power tubes and rectifier though.

The current production preamp tubes don't usually last as long as the old stuff, but still a few years.