Power Tube Failure

It’s a tube. I’d not be concerned. 

A tube tester can’t predict failure.

Also signal tubes if they blow should not damage your amplifier because they don’t carry a lot of current. A power s different and I guess is more likely to damage amplifier if it has a catastrophic failure. But if it’s a well built amp there should be some protection built into the amplifier to prevent damage.

I’m waiting to hear for bad sounds on my amplifier. I’ve got 28 tubes and I’m not going around and testing them all the time.

Maybe a tube tester is a good idea. I have some NOS tubes which I’m finding are unpredictable and when I change out my tubes I’m probably going to live with recently made tubes. I purchased some small NOS tubes made by Telefunken and had to replace many of them after 1 year of service, They seem unpredictable. The power tubes I’m using are stock tubes and when they go I’ll replace with probably golden lions because that sounds like a good cool thing to do because of positive sentiment and because the name of the tubes is really neat.

So fancy old NOS tubes are too risky for my amplifier and despite the source of where the nos tubes came from which is very credible I’ll probably never buy another NOS tube. 

I find that going back to solid state amplifiers is difficult because they really don't sound very good and the distortion is different and crude. Although some of the well-made solid state amplifiers which are very very expensive might be worthwhile but generally I don't like solid state at all. I have McIntosh 611 solid state and they're very nice but listening to mid range and vocals is not as good. Overall they are just not comfortable to listen to. But I need them for back up in case one of my tube amplifiers goes bad.

NOS authentic Telefunken quitting after one year ? Something is wrong here, it shouldn't happen.

Mullards 12AX7 long plates from 1950s in my VAC have about 2500 hours after two an half years and keep going. I expect 2500-5000 hours more out of them.

I own a Raven Audio Nighthawk (upgraded) which has been my daily joy for several years now. Several pre amp tubes and power tubes have failed. They will tell you immediately when they are about to "give up the ghost." The most 'exciting' event is when a power tube "red plates". It will begin to glow red in a major way throughout the main body of the tube. But more 'exciting' is the distinct and undeniable howl it begins to make as it expires. One must hasten to shut off power immediately or else severe damage will be done to your amp. (And left to proceed with power left on, maybe a fire will break out). Pre amp tubes will simply sound hummy and crackling/popping etc  These events most frequently happen upon start up. Its never happened (to me) after the amp has been running quietly for a few minutes. However, unlike solid state units, one may want to keep an ear tuned to the music just in case. In any event, if you want background music you may want to use the radio instead. Why bother with this? BECAUSE....Tubes sound like real life. Solid state, doesn't (until you spend above $5 -7 grand on nice separates). At least that's what I've experienced in my days since I was a young stereo salesman in 1978. I am a certified fossilized geezer.