What Happens When Preamp Tubes Need Replacing?

When preamp tubes need replacing, how do you know? What are the tell-tale signs sonically and otherwise?

Thanks in advance.
New noise, typically hiss crackle and pops, but also hum.

The sneaky one is that gradually the tubes become rolled off and lose lusture. Pays to have an identical set about and every year or so plug them in and see if there is much, or any, difference. Good to do also because you will be cleaning the crud off the pins as the friction involved will scrape the pins.
Brilliant idea, thanks Newbee.
I begin to sweat and fret and worry... about the expense of the new set.
Ouch..., I had conveniently blanked that out, could get rough with the ol' ECC803S Telefunken
Ah, the expense of driving in the fast lane! As has been pointed out many times, if you can 'afford' a Ferrari in the first place who cares how much maintenance it takes or what mileage it gets. And in todays market a few extra tube sets are probably a better investment than in the markets or anywhere for that matter.

I'm continually amazed that such frugal folks as you two guys can actually destroy these NOS tubes by using them. :-)
old tubes make your rig sound boring and lifeless.
My wife must have old tubes...

I run two Telefunken ECC803S tubes in a phonostage. I don't have an extra pair, so I am relying heavily on their reputation for outlasting the owner. Yes, they are now shockingly expensive, but, I have not heard anything close to that tube for clarity, and dynamics.

Other than for crazy expensive tubes, I agree that having a spare set to compare the current operating set is the most sensible way to tell when tubes need to be replaced. I have a tube tester (Amplitrex) which is helpful, but it really does not necessarily identify when a tube should be replaced because it is beginning to SOUND bad. I have some really old and worn Tungsol roundplate 6sn7s that test extremely weak, but, in my particular amps, they continue to sound pretty good.
He did say " ...how do you know..."

I've not sweated in a good long while.

Never due to tube breakages or burnouts. Only from one of two things have I toiled over tube replacements. My own desires for them, or those tubes which came with the device were overstated as to their wherewithal.

Primarily it's from my desire to have fresh, or try some other flavor.... but I think that's about the same thing... isn't it? Somebody's buying some tubes for some reason.

As for the Ferrari notion.... yeah one would think so. I did.

OK buy another set of tubes right off with your new "I'm keeping this for ever item"

Then, suprisingly, forever comes along a lot sooner than you had thought it would and for whatever reason a new toy seems a better move to acquire.... and it doesn't use the same tubes.

I've got a fair number of matched pairs of Amperex and Telefunken 6DJ8 CLASS tubes presently with nothing but a box to put them in. PQ US 7308 WHITES, 7308 greens, orange, Tele cc88, ecc88, JAN Phillips 6922, and some others I don't even remember.... RCA & Amperex 12AT & 12AX, Tele’s as well, Tungsol minis, Ge minis, RCA minis, and none have more than 100 hours.... and no one will buy them.

I offered them all at well below the going rates a year ago with no activity whatsoever.... cause they were used I suppose and I had nothing other than my own feedback to account for them…. No recently tested figures maybe was it. Beats me, but all those tubes are proported to have upwards of 10K hours of life. So what’s 100 or so if priced very attractively?

It’s cause their used now. IMO

Or maybe it was the timeing.... it sure wasn't due to their pricing.

It's a nice idea to have auxilliary fresh tubes about, but then there are indeed pitfalls.... for as soon as you plug 'em in and try 'em, you can no longer sell them as NOS... and that can hurt.

What too if your gizmo has four, six or eight tubes instead of one or two>? Or several types in it’s topology?

A tester for those who can use them seems the best idea. Then there’s calibrating that too.

I went one other way to figure out if tubes were going on me or if a tube run device was causing an issue. Buy new cheap same types, or another SS likewise component, chealy.

You can merely swap a two tube devices tube about as well. Putting the left onto the right side and so forth.

When the Ferrari is gone however, What ya gonna do with the spare parts left behind?

I can dig you all here about having on hand another NOS set, but new costs way less and does the same deal.

Managing the entry fee alone is tuff enough at times. Anteing up for all the tangential expenses of operation up front is off putting, regardless the wisdom of it at the point of sale.

In any case... I'll continue to sweat and shiver when that time comes.... and it will I'm sure. ;-))
My wife almost tied her tubes around my neck when I wanted to buy new ones but she forgot for a moment she already had em tied. I survived and got a new set of EL34 Ruby's (12) 2 12AX7's 2 EL84's. Of the 14 old tubes EL34's 1 had a short 2 were in the replace zone. All others were fine but they will only be for back up. Just get new tubes that MATCH and it makes a hell of a difference. If a tube tester costs more than a new set of tubes use someone elses tester. BTW why do some people knock Ruby EL34's? They sound great to me.