noob toob question

Hello Ratsol,

You will need to be more specific as to the brand and model of amp/preamp for others to be of help to you. This way you can get an accurate answer and know what to expect from your equipment or the equipment you are interested in.

I own BAT tubed equipment, the beauty of them besides sounding "freakin' great" is that when a output tube goes on their amps you will blow the corresponding fuse for that tube. You flip over the amp replace the fuse and if you blow the fuse again you can be pretty sure the corresponding tube is bad and needs to be replaced. It has auto bias for each tube so no need to futz around with that.

In general when smaller signal tubes start to go in amps or preamps the sound usually starts to sound dull, rolled off highs, bass is not as well defined, less dynamic, the sound becomes slow and boring. Hope this helps a little.

Good luck,
Tom

Old tubes will just fade away many times until they flare a little on turn on and ___. The amp will sound weak/thin/lame before this happens usually.
When tubes "blow", many times it may be the amp's fault. If I blow a power tube that I know tested good, I would usually want a tech to check it out before I waste a new set of tubes. You don't want to replace just one.
However, tubes are like light bulbs and just blow sometimes. I've seen them not do any harm and I've seen them damage and amp in the process also. I've never experienced a tube hurting any other gear than the amp it's in.

How do they leave thee? Let me count the ways: (1) The estimated life of some tubes is based on the heater element(just like a bulb filament). They burn out the same way. (2) Then there is the gettering- The shiny stuff either on the top or bottom(on older tubes). It gets thin and see-throughish as the tube ages. That will weaken it's output. (3) Repeated turn-on voltages applied before the heater has created an electron cloud around the cathode will cause it to "strip", also weakening the tube. That's usually only a problem if the operating voltage for the power tubes is brought up too fast(for instance by replacing the tube rectifier with a solid state unit). (4) I've had tubes that made snap-crackle and pop noises during play, which(to me)indicated a bad internal weld(connection). Popping them with my finger would bring them back to normal for a while, while I secured replacements(most of those were small signal tubes like 7199s, 6DJ8s, etc). (5) I brought an amp into the house once from the cold of a winter night, and couldn't wait for everything to reach room temp before turning it on. YEP- The glass cracked on a NOS EL-34. (6) Sometimes the tube envelope will leak of it's own accord though, and the tube will get gassy and burn out(hopefully you'll notice the color change in it's glow, and get it out of there first). (7) Then there are the miscellaneous internal shorts that may take out a resistor or cap, if the tubes are not individually fused. Sometimes you'll hear a pop, sometimes not. (8) If the bias is user adjustable- Some run it high and shorten the output tubes' lives that way. I've never had a really dramatic tube failure in the past 28 years, but- I'm certain they do happen. Capacitors exploding occasionally is about as exciting as it's ever gotten for me. I've probably missed some of the potential failure modes, but these will give you something to look forward to.