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I've only recently become an avid listener to a tube headphone amplifier set-up, some days powered-on for many hours at a time, so I really don't know what to expect in terms of tube lifespan. The notion of a frog placed in a pot brought slowly to a boil, and death by a thousand cuts come to mind when I think of, "How will I know when to replace my tubes when the time comes". Should I buy a replacement set in advance in order to hear if there is a notable improvement now and then, or just hope that audible indicators such as noise, or unusual warm-up time might be signs. Otherwise, I don't like the idea that I'll find myself feeling as though my tube set-up is sounding sub par someday, and realize I had been listening to a tube amplifier that would have brought more enjoyment if I understood the warning signs a bit earlier. TIA
Follow Ups:
I find it strange that some spend big-bucks on an amp, only to operate it without any form of maintenance until it sounds suspect.I guess the example is a pricey vintage car - drive it till you hear strange noises from the engine or brakes, and then get it repaired, or change the oil and filter. At least cars have an odo, and a maintenance log-book, and try to get the owner to keep the car safe and operating efficiently.
There are relatively cheap maintenance processes for checking the health of an amp. With the car example, not everybody has the mechanical/technical nous or equipment to change the oil, check fluid levels, run automated tests, etc. Some amp maintenance processes require electrical competency (eg. to measure idle voltages and currents around the circuit), and some require technical nous (eg. to measure distortions and frequency response).
Edits: 12/29/20 12/29/20
First off, your input tubes are probably the most critical to the sound. Get then right, first.
Second, often there are more than one output tubes and you will buy in matched sets so that you always replace those tubes together.
Mistake!
I think it is better to replace only the bad tube and do not throw away any good tubes. Save them if you must swap them out.
Eventually, you will find that the good tubes last far longer on average than any new replacement.
That's just tubes for you. There's a lot of variation in longevity (and I'm not even going into sound for the same manufacture of tube).
That's been my experience.
What you are wondering about and others are describing is the exact reason that after years of fighting the good fight I ultimately gave up on tube gear. I have been the frog in the slowly heating to boiling water too many times. I had mostly EL34 based amplifiers and often used KT-77 tubes with them. I had a set in my amp from new for about a year of moderate listening and when I replaced them with another set of KT-77s I could not believe what I was hearing. I was like "holy crap! my speakers have tweeters again". I had forgotten how good the amp actually sounded".
On a KT-88 amplifier I ran the tubes for about 6 months of fairly heavy listening and tried another identical set of KT-88s and while the used tubes still sounded perfectly acceptable the fresh tubes were a very obvious upgrade in terms of SQ. Highs were airier and there was just more information in the music.
If a tube has "lost it" at 2000 hours has it half lost it at 1000 hours? Quarter lost it at 500 hours? In my experience the answer was "yes". Even 2000 hours is less than a year averaging 6 hours a day. 500 hours is less than 3 months of that much listening. Best case scenario you are only averaging 3 hours a day and you ride the tubes out until they are obviously worn out. That's going to cost you $200-$600 in maintenance every two years depending on what you are running. That's a pretty high cost of ownership and that's assuming you ride the tubes out until the bitter end and are okay with lower SQ during year two. This also assumes that a tube doesn't fail prematurely which does happen more often than tube users are willing to admit.
The final nail in the tube audio coffin for me was hearing newer SS amps. SS amps, especially headphone amps have come a long way in recent years. What they lack in midrange bloom and pleasantly rolled off highs, they make up for in overall fidelity, accuracy, and longevity without replacing parts. In the past SS amps have been known to cause listening fatigue but based on what I am hearing now I really think that's a thing of the past.
Another thing that helped smooth the transition was the discovery of what R2R based DACs could do. IMHO I have found that they offer much of what I like about tubes without any of the pitfalls of actually using tubes.
...I always tell them that tubes are like people. There is the average life expectancy, but there are many parameters that affect the actual life.
On top of that, just like people, they, and their sound, start changing from the getgo.
Unfortunately, in many cases the only way of knowing when to replace them is by trying a new set.
You can also just enjoy you life. :)
Life is too short not to enjoy listening to tubes after a solid state mentality over many decades.
As much as I still do enjoy the somewhat analytical perspective of solid state gear, the undeniably natural feeling of tubes is ergonomic.
My body feels better when listening to, and evaluating various audiophile listening cues via tubes. Better "Boogie Factor", too.
Cheers, Duster
BTW, send a message to me via the Audio Asylum email system if you'd like to chat, Victor.
My experience is 5000 hours for small signal, and 2000 hours for power amp tubes.
Some PQ small signal can go 10000 hours.
Some will fail much sooner, it's a mater of luck and amp design IMO.
Depends on the tubes and the amp.
I design circuits that take are of the tubes and I expect over a decade of life. No sudden failure; no premature aging. I do have back-ups ready to go and don't think about the aging thing.
But I don't know what tubes or amp you are running - could be different situation for you.
"Confusion of goals and perfection of means seems to characterise our age." Albert Einstein
Yes, always have spares on hand - always.
You may not need any for 10,000 hours... or you may need one in the next 5 minutes. (I did get over 7,000 hours out of a quad of KT-90's once.)
WW
"They were running on fumes, dazed and confused, in a high-powered automobile."
Tube life is dependent on more than just the hours used-
though that is a great place to start-
Input tubes - 12A_7, 6DJ8, and the variants should be good for 10,000 hours of run time
Power tubes are less - but here we really get into the circuit-
If the tube is biased hot, then start the subtraction machine...
The Old Quicksilver amp based on 8417 output tubes might last 6 months per pair -
At the other end, McIntosh and early Marantz could easily deliver years of enjoyment from a set of output tubes.
Happy Listening
"If the tube is biased hot, then start the subtraction machine..."
What would constitute a hot bias?
February 26, 2020: "You have fifteen people, and the fifteen within a couple of days is going to be down to close to zero,"
It really depends upon the tube -
and in truth it is not just the bias - but the power you are pushing into the tube to get the amplified music out-
Tubes have design specs - and generally they should be adhered to
There are designers who have pushed the ratings and get long life, there are others who push the envelope and get short tube life-
The Tube specs are not always easy to decipher-
From the RCA RC-30 Tube Manual- for the 6CA7 - Class A, Plate voltage, 800v, bias current 150mA
but in the next section, Class AB1 - Plate voltage 450, with a 'zero-signal plate current' of 120mA - which is the bias current w/o signal- or idle current...
So in a PP Amp using this tube - running a bias current above the 120mA would be 'hot' at a plate voltage of 450
But class AB1 is a bit of a sliding scale - and the place on the scale is determined by the bias current....
As with a sailboat, the design is a compromise.
For a sail boat, the line goes: Speed, Comfort, Sea-worthyness - pick two!
Happy Listening
I'd be lying to you if I said that I understood that . . . .
But I do like the way that they sound.
7-5-2019 "Our army manned the air, it rammed the ramparts, it took over the airports, it did everything it had to do, and at Fort McHenry, under the rockets' red glare, it had nothing but victory."
I would also add to my previous perceptions (of output tubes getting tired) that turning up the volume makes things worse.
February 26, 2020: "You have fifteen people, and the fifteen within a couple of days is going to be down to close to zero,"
What tube are you using? And the amp?
Depending on the what and how of it, there's a chance the tube may outlast you.
But, it's always wise to keep known good spares.
I don't know what the tubing is like in a headphone amp, but in my main amp & my back up amp for my room system, when the outputs have started going/have gone south (this recently happened) I first note female vocals getting hard, edgy, grainy. I also note that the sound stage begins to compress. When it really gets bad, like it had degraded to recently, bass gets really loose (that's the best descriptor I can think of) & the highs get fluttery sounding, or maybe reedy (as in the reed that inserts in the mouthpiece of a woodwind instrument). My bias readings also do some goofy things.Those are my perceptions.
I have considered keeping a spare set on hand (for the amp that now serves as my backup, I actually have accumulated, via tube rolling, 3 serviceable sets of outputs--but it only takes 4 outputs). I don't know why I haven't for my main amp. Cost I guess, my main amp uses twelve EL34s. I actually do have a few different inputs to roll (someone, who remains nameless because I don't know if he would want me to thank him publicly, recently gifted me several more) & I have four pairs of power source tubes, and I know for sure that two of those pairs are serviceable. The extra inputs & power source tubes have came in handy, & due to using those, I recently concluded that it had to be my outputs that were getting grungy, & sure enough, that was the right conclusion.
This statement in your OP rings true for me:
" Otherwise, I don't like the idea that I'll find myself feeling as though my tube set-up is sounding sub par someday, and realize I had been listening to a tube amplifier that would have brought more enjoyment if I understood the warning signs a bit earlier."
It does, in fact, bug me that my listening sessions were degraded because my outputs had lost their sheen. I felt something was wrong, but I wasn't sure if it was just me having some bad days. Finally, I couldn't listen in denial any longer so I took the plunge, & tonight I realize how better served I would have been doing that earlier. But I wasn't sure. A spare set would have let me verify those feelings or refute them.
7-5-2019 "Our army manned the air, it rammed the ramparts, it took over the airports, it did everything it had to do, and at Fort McHenry, under the rockets' red glare, it had nothing but victory."
Edits: 12/10/20 12/10/20
Recently I just heard the exact same symptoms as you described for bad tubes, when listening to my Transcendent Sound OTL tube amp.
Sure enough, I bought a quad of tested and matched EL 509s from the bay (a tube seller with almost 2000, 100% feedbacks) and installed them today.
After settling in and rebiasing a couple times, the amp is sounding great again.
The symptoms you described match perfectly with the issues I was hearing...
If art interprets our dreams, the computer executes them in the guise of programs!
Yes, for all the stupid stuff I will spend money on without batting an eye, I don't know why I stay in denial with output tubes for so long. I would find a spare set truly handy, for the exact reasons that the OP suggested.My system was sounding so horrendous that after the last time I listened to it (about two weeks ago), I hadn't turned it on since. The USPS has been running like the pony express lately & also without any kind of decent tracking, so I was just about ready to haul my other amp down & set it up. That was more work than I was up to though (those tubes should be here today, I kept thinking) . . . .
Oh well, abstinence makes the heart grow fonder.
February 26, 2020: "You have fifteen people, and the fifteen within a couple of days is going to be down to close to zero,"
Edits: 12/10/20
I'm lucky I have two dern good backup amps. A Musical Fideltiy Class A A1 (2008 version) and a QUAD 909.
Really everyone who runs a tube amp should probably have a decent backup.
I am keeping the QUAD and waiting for the Magnepan LRS to be available. I want to try out planars and the QUAD should drive them acceptably.
If art interprets our dreams, the computer executes them in the guise of programs!
I still have my first tube amp. (Your first tube amp is like your first [fill in blank], right?)Anyway, it is a Cary SLA70 Signature with two 6550s per-side that I bought in '94.
Being as it was my first, I truly didn't have a clue, & when the first set of outputs started losing their bloom, I felt it was just me, & I stayed in denial way too long. Back then I was in a life period where I was really mesmerized by the sound of Margo Timmin's voice (female vocalist for the Cowboy Junkies) & when it got to the point that I just could not bare to crank "Sweet Jane" up to bigger than life levels, I called Kirk Owens, from Cary Audio, & asked, "What's up? Do I need new output tubes? Don't they last forever?"Probably, & no they don't, he replied. The amp came with Svetlanta 6550Bs & it must have been about at that time that the Svetlanta 6550c came out, as that is what Kirk sold me.
Anyhow, the new tubes came & I put in The Cowboy Junkies & things just didn't sound like I wanted them to. So I called Kirk back up & told him what I was hearing (or not hearing). He sounded a bit perplexed but The amp was still under warranty so he said, "send it to us." He called me after he had had the amp for a bit & told me that he had it on the scope & had been playing it all day & it sounded good & read good . . . . I asked, "Do tubes maybe need to break in?"
Haha.
But, you see, this was my first tube amp & when I fired it up the first time I had nothing to compare it to, & as it gradually got better by degrees, I didn't even realize what was happening.
So, as long as Kirk had the amp anyway, I had him put the oil filled caps that Cary & Cary dealers were always raving about.
So all was not lost.
Cary used to have great customer service back then.
7-5-2019 "Our army manned the air, it rammed the ramparts, it took over the airports, it did everything it had to do, and at Fort McHenry, under the rockets' red glare, it had nothing but victory."
Edits: 12/11/20
Most common tube testers can't even test for noise. Having a backup set is the best idea if the cost is within scope. But, of course, tube ownership is the gateway to tube rolling, so I would not be surprised if you purchased alternate brand tubes to add a little flavor.
I also think that the longer you own tube gear, the more likely it is that those thoughts will recede into the background as you focus on the positive virtues of tube ownership. Enjoy the voyage.
In terms of tube rolling, I found the keepers for my set-up, and fortunately a set of the Russian tubes are not too expensive as a back-up plan for a low-power headphone amplifier. I have enough orphaned tubes to check the status of my keepers, or troubleshoot in case of any 'questionable behavior', but I might get fixated on the different presentations and forget what I was trying to do in the first place...
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