Preamp Eats tubes..

Unlike wine, I don't thing age improves tube performance or longevity.

Do you have a tube tester? Are you sure about how new your supply of 'NOS' tubes are? If you don't own a tube tester, maybe your NOS tubes are not as new as you think they are.

I haven't heard of the Sonic Frontiers Line 3 being a 'tube eater', but if you're sure your NOS tubes read good before you burn them up, maybe there is something wrong with your Line 3. Possibly bias or something is out of whack. Contact Chris Johnson of the Parts Connexion.

It could be that your preamp does stress the tubes, so that only truly rugged tubes, like the Sovteks, can handle it. It may be that your preamp, is similar to the Audible Illusions preamp that is mentioned by Joe, of Joe's tube lore fame.

The following is a portion of Joe's Tube Lore, which is on Audio Asylum.
(I hope it is okay to post this hear, as it is only a portion of an article, and I gave proper credit, I think.)

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Special warning to Audible Illusions preamp users:

The one you can say for the Sovtek is that you can run it hard and it can take it - and apparently that’s exactly what AI does. Unfortunately the classic NOS tubes in this family just cant take this kind of treatment and will rapidly fail when used in these units (and some of you guys have the fried tubes to prove it!). So you AI users are probably best off limiting yourselves to the Sovtek, the Russian 6H23N & 6N1P, the 7DJ8 and the E288CC. There may be others the range of tube types and variations is quite literally bewildering but these are the ones I’m aware of that should be able to handle the higher stresses of this brand of preamps. I review the Edicron, Siemens E288CC and 6H23N here but there are other brands for some of these. I’ve seen Phillips E288CCs & Amperex 7DJ8s advertised on some web sites in the past and there are probably others. It might be worth your while chasing them down & evaluating them for yourself to increase the number of alternatives for use in your AI.
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(I don't know for a fact that your preamp is over stressing the tubes, but it sounds like from what you write. Good luck in your search for the magic tube for your use!!)

it's possible that the NOS have slightly different specs and aren't a good match for the SF circuit. my CAT pre is picky that way - it also likes the Sovteks better than some NOS I've tried.

Sounds to my like you need to get another tube supplier....

i know there are big changes nfrom my SFL1 and your unit, but I leave mine on 24/7 and have atleast 8 months on a used tube a fellow Agoner gave me.

Not all wines improve with age my friend....Some should not be laid down at all.

I would contact Chris Johnson at parts connection regarding your pre (he built it) I have used Amprex bugle boys and orange globe with no problem and long life with a line 3 before.

you should inspect this preamp for proper steady voltages and currents.
you can get this information or detailed schematics from partsconnexion.com as well as great technical help from chris. or you have to have it done by a qualified technician.

Assuming the preamp is not malfunctionning, you almost certainly won't have a problem if you keep your preamp powered up 24/7. It is dead wrong that running small signal tubes 24/7 shortens life -- the studies done in the 1950's proved the exact opposite. With few exceptions, such tubes last basically forever if they get past the infant mortality stage (+/- 250 hours) and are left on constantly. Counter-intuitive, yes, but true -- just like transistors, it is thermal cycles (i.e., turning things on and off) that kills electronic components. Many tube preamps also do not ramp up power to the filaments at turn-on, the tubes getting kicked in the groin when the power hits them.

Output tubes have to be turned off when not in use because they pass a lot of current and thus wear out relatively quickly.

Raquel,

on quite a few preamps the preamp tube are peak-driven like a power tubes and so the life of them will shorten significantly when left on 24/7.

in power amplifiers the bypass electrolytic caps can wear out faster than tubes turned on 24/7 thus resulting very often overbias and dead tube thereafter.

Marakanetz:

The preamps to which you refer are relatively rare. I would qualify what I wrote by pointing out that preamps using tube-regulated power supplies cannot be left on 24/7, as the tubes in the power supply are relatively stressed.

Tube amps are not the issue -- they can't be left on.