Question about valves running hours


I'm new to the tubes world and when I bought my amplifier the seller told me not to run it for more than 8 hours, letting it for rest a couple hours before the next listening session. I wasn't told why, but now I got curious and I want to know more about it. 
What's the reason for this limitation? What can we damage and why?
Convert?fit=crop&h=128&rotate=exif&w=128migueca
What amps are you referring too? I have not heard this recommendation before with any tube amp. Maybe he was referring to a break in period?

jb
On/off cycles are much harder on any electronics, than hours.   Outside of heat, a tube's biggest enemy.   
For tube electronics, I completely agree. Tubes must rest. On/off cycle of tubes is relatively easy and lasts 5...10min. 
The advice of seller is RIGHT ON and should be followed.
Tubes run hot and dry out capacitors. 
Turn off tube electronics if you don't plan to listen to it for more than couple of hours
Turn off tube electronics before you go to bed and before living dwelling!!
This will assure longer life of your equipment.
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On/off cycling during listening sessions is ridiculous.   Absolutely turn off tubed gear, when not enjoying your music.   I didn't mean to imply otherwise, in that first post.
" On/off cycling during listening sessions is ridiculous".
It in fact is unless the listening session is way too long as mentioned 8 or more hours. Give yourself AND amp rest for at least few hours.

I don't believe the OP was talking about on/off cycling during a particular listening session.  But resting the equipment between listening sessions. People are different and have different schedules.

I am not retired and work during the day.  When I get home and feel the need to sit and listen and enjoy music, I turn my system on about an hour or so before listening and when done (because I have to go to bed and sleep to get ready for work the next day), I turn the system off.  I think this is mostly true for most people.

Retirees on the other hand, may listen for a few hours, leave to run some errands or some such and come back home and want to start listening again.

No big deal.  I would still turn my equipment off anyway.  Modern equipment should not have any on/off cycling and current inrush issues because they have inrush limiters or slow start circuits that limit inrush.  Also, some electronics don't have circuits that drain capacitors when off, so many times the capacitors still have a charge on them anyway after a few hours, so again, there is limited inrush current.

The only cycling issue would be the switch itself and maybe the bridge diodes.  But, I wouldn't count on that either.

If you are going to leave for a few hours, I would turn the equipment off.  If it is solid state, (with exception of class A amps), there shouldn't be a problem leaving them on.  Like I said, personally, I would turn it off anyway when I leave.  I don't like having electronics on when I'm not home.  Refrigerator notwithstanding.

But, leaving tubed equipment on that don't have standby circuitry is simply asking to replace the tubes much earlier than necessary.

enjoy

Thank you all for your comments. 
My amplifier is a push-pull from Cayin. 
When I bought it, the lady in the shop told me to run it for periods no longer than 7 to 8 hours due to the heat. And to wait some time before turning it on again (I understood waiting around one hour or too, but maybe some minutes are enough).
I couldn't ask for more details because her English was poor and I don't speak Chinese! I'm living in China...
So now I'm just trying to get your thoughts about this matter to better understand my amp. 
That makes no sence at sll. I recently bought the Excellent Jolida 
Fusion 3602  integraded amp.with a bunch of of upgraded parts including the Excellent 
Rike Audio paper oil capacitors that take 300 hours to break in.Check out their Amplifiers  $300,000+.
I have used Vacuum tube gear for years as of today I have been running this Integrated amplifier one week straight 24-7 with 
Vintage  output and phase splitter tubes, the second week changed out the EL-34 tubes  input tubes after 175 hours ,and installed KT- 150 Vacuum tubes just flipped a switch on back. Factory stock tubes are guaranteed for a minimum of 1,000 hours of play time.Vintage tubes many times that .
If your amp is built correctly it should have a stand by circuit, as well as a slow start so a surge  of voltage doesn't shock the tubes on start up.
Also manual bias of the larger input tubes is much more accurate 
Way of biasing the individual tubes ,auto biasing has a bunch of resistors to average the circuit which in turn takes away a bit from the accuracy a bit overall.this several engineers Have said as a purist approach. 
My work system is driven by a 55 year old Masterwork amp (by pilot).  I use it for 8 hour work days all of the time and it never fails me.  It does get hot but I make sure it's well ventilated.  If this amp can take the abuse without ever burning up tubes or caps, why can't a new one? 
To further clarify. Like myself I wanted to completely runin the circuit
And left on for 300 hours non stop. My amplifier sits on top of rack 
And heat is not a issue tubes are made to dissipate heat mainly from the Larger input power tubes with no issues,or danger.any quality 
Amplifier has safety circuitry between the digital circuitry,as well as fuse. Good power tubes you should get at least 3,000 hours . My smaller   preamplifier tubes all are Vintage  1950s
Vintage tubes on average at least 10,000 hours possibly much more.
Onot any amplifier brought into the U.S check for U.L approval  . If not it has not been  verified and Electrically approved.if bought on Ebay 
Verify before buying. In Europe EU  approved.in the U.S you cannot Legally sell  without it ,or face $$ liability if something happened !!
Migueca, I do not want to alarm you, but it looks like the Cayin is of Chinese origin?

Several years ago I purchased a Raysonic sp120.
Designed in Toronto, built in China and CSA approved.

Turns out the power transformer was not really rated for 120v

This elevated the heater voltage and caused the tubes to fail early due to overheating. My expensive Gold Lion Tubes failed after 3 months

I did talk to Raysonic, but they refused to acknowledge there was an issue.

I had it fixed for $300 by an excellent tube technician and it sounded so much better and the tubes lasted almost a year after that - played 8 hours daily

I would have the amp checked by a good tube guy - could save you a lot of money in tubes alone.

Now I know some will say a lot of gear is made in China and works fine.
- mine is just one of a miriad of tales about kit made in china that was less than perfect.

The SP120 was my first a last tube amp, so I was pretty green - in more ways than one.

As for the 8 hour limit, I’m with most others opinion, turn off when not in use - you’ll save on hydro

Regards
Williewonka, sorry for your bad experience with that Chinese brand, but Cayin is a well known reputable name. Their products are top notch with lots of good reviews all over the world. Doesn't mean that a product coming out of their shelves couldn't be defective, but lets assume my amplifier is all good.
I guess all of us agree that the major issue when running valves for a long long time (more than 8 hours) it's the excessive heat. And heat is what shortens the life of a valve.
As for having to wait some minutes prior to turn it On again, yesterday someone told me that it is important because of the capacitors (?). It seems they have to "discharge" or dissipate their energy before we connect the amplifier again.
Anyone with a good simple explanation about this? 
Migueca, Glad to hear Cayin are top notch.

Re usage: Tubes have been used in broadcasting 24/7, so using for more than 8 hours should not be an issue in quality built amps.

But to extend tube life a d reduce hydro bill, power down between listening sessions.

And..... enjoy ☺


Doesn't  anyone remember?Vacuum tubes powered WWII.
Doubtful equipment was on a timer and shut off after 8 hours.

That being said, it doesn't mean keep it always on, just turn it off when you're finished listening. It is a good idea to at least have the amp in an open rack  or top shelf for ventilation.



Agreed-

Heat will kill a tube.
Another pertinent question: If valves were the power support to all communications in a recent past (from tv and radio broadcast to military coms), for how long would they live? Would a valve survive more than a few hundred hours? Were they replaced many times a year? Or did the equipments have different banks of valves to switch between them? I'm curious about how people used to operate the tubes 50 years ago.
migueca- I don't know about military/industrial practice, but back in the '60s, it was pretty common for tubes (and free standing tube testing machines that looked like ATMs in size) to be everywhere- drug stores, hardware stores, electronic specialty stores (like Radio Shack and Lafayette) and other places. It wasn't uncommon for a civilian appliance owner to take a set of tubes to such a shop, 'test' them, and buy replacements.  (Sometimes, the new tubes were on shelves behind a door at the front of the testing machine).
If it was a big TV/console and the owner was not equipped to do this, there was a business-- the TV/radio repairman, for lack of a better term- who would show up at your house and do the work. People generally weren't fawning over Telefunkens with specific markings; GE was a pretty common brand at least in the NE States and for these purposes, a tube was a tube, there were 'equivalents' that you could look up (still available as pages on the 'Net) and it all seemed pretty matter of fact. By the mid-'60s, I guess, transistor stuff became more commonplace, but the tube regime hung on well into the '70s or later as a fairly common artifact. (I'm not talking about audiophile or specialty applications, just garden variety tube usage, availability and replacement). 
Whart -  thank you for that "History class" :) It's really interesting to learn how people dealt with gear in the past - this case, valves.
It seems a valve was something simple and common, like a light bulb.
My pleasure. Obviously, that was the States. Other countries, practices varied, I would assume. (Hey, in London they still have a store for barrister wigs and a store devoted to umbrellas if I recall). I'm also pretty confident that the big tube Vlad Lamm uses in his SET amps was long used by the Soviet Union as part of the guidance system for their ICBM (nuclear missiles). It's a pretty robust tube! 
The heat is develop when the power tube plate dissipates,the more watts the more heat and the more heat the  shorter the tube life.A well designed amp should have about 60-70% of total plate dissipation
If the amp is biased correctly it can play long periods of time without issue.  I listen to my amps for hours , I do turn them off when I go out though, but cycling the power for short periods actually shortens tube life
Tubes are like incandescent lamp bulbs. They wear out in time, and switching them off between auditions helps lengthen their lifespan. One set of tubes will last for let's say, two to three years (daily use) without losing the sparkle in the treble range, and I'm talking about audiophile-quality use here. Their turning on and off causes temperature changes to the internal elements and this is what shortens their life. It's advisable to turn them some time before listening and letting them warm up to music. An ageing tube loses the top end, then the mids and then the bass, in this order.
The owner's manual for my tube amplifier advises that to increase tube life that it not be left running for more than an hour if it is not being used. Along the same line, a comment made in the owner's manual for my (tube-based) media player is that unlike solid state players tube output stage players should be shut down when not being used.  This will greatly prolong tube life.
Migueca,If the input voltage is not the  same as in the US,It affect the filament voltage and it's not 6.3 volts anymore and that's why tubes have shorter life if they are not rated.