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How long do tubes last?

post #1 of 14
Thread Starter 
How long do rectifier, input, and output tubes generally last? In particular I use 12AX7/5751 , 5AR4, EL34, and EL84s types. I'm thinking I should stockpile some. Not in the quantity as Hirsch though. I just like to keep mine on for like 12+ hours a day.
post #2 of 14
Of course the answer is, it depends. Smaller signal tubes, such as the 6DJ8 are rated to last about 5,000 hours and the more durable versions will last incrementally longer. An output tube is typically thought to last 2,000 hours, but then you are talking about using them to drive speakers. When used in a headphone amp, such as the EL-34 in the ASL MG Head, the demands will not be so great, as when driving speakers, so they should last longer. But running them 12 hours a day will still put a good bit of demand on them. I am sure that there is someone with long term use of these tubes in a headphone amp that may be able to provide real life experience on the life they have gotten out of their tubes. If they have kept their amp that long that is!
post #3 of 14
The tube types you listed are all common types that are currently still in production somewhere on the planet, so I doubt that there will come a time during your lifetime when it will be impossible to get EL34 tubes for example. If you find that one type of 12AX7 or 5751 tube is a favorite, better pick up some spares now, because while these small triode tubes are still in production, the new production ones may not sound as good in your system.

It is generally accepted that while they can sound as good as some of the vintage tubes, current production tubes do not last as long as their aging counterparts. This is due to changes in manufacturing techniques, specifically how long each tube is placed on a vacuum pump to have the air evacuated. To keep costs down, tubes are evacuated for a much shorter time than in days of old.

If you want your tubes to last as long as possible, running your amplifier all of the time is one way, although it wastes electricity and generates heat into your home, even when you are not listening. Like a light bulb, most of the wear and tear on a tube occurs during power on. High quality tube radio gear, ham radio and commercial broadcast equipment. includes a standby mode that keeps power applied to the heater element of the tubes and all of the other tube elements, except the B+ voltage normally applied to the plate. So minimal power is being used when the gear is in standby mode.

If you are using a tube amplifier, integrated amplifier, or receiver, adding a small fan to direct air through the chassis will greatly increase the volume of air circulating through the unit, thus lowering the operating temperature of the tubes and other components. This will extend, by two times or more, the life of the typical power tube. Given the cost of replacing a set of NOS tubes such as Mullard EL34 type tubes, this can be a real money saver.

If it is a vintage tube unit, use a variac and keep the operating voltage to 110 volts. This reduces stress on all of the circuit components, especially the high voltage components, and also lowers the operating temperature.
post #4 of 14
Quote:
Originally posted by mkmelt
If you find that one type of 12AX7 or 5751 tube is a favorite, better pick up some spares now, because while these small triode tubes are still in production, the new production ones may not sound as good in your system.
There are two very good new production 12AX7's right now. The Elite Gold 12AX7EG is a very nice sounding tube, that is better than many NOS variants. I pulled the Telefunken smooth plates out of my Fisher 400 in favor of the new Sovtek 12AX7LPS. It's that good. My Fisher is sounding the best I've heard it.
post #5 of 14
HIRSCH

How about NOS 12AX7 RCA Blackplates. I just bought a pair for my jolida jd100. I have not heard them yet but wanted to know your opinion on those and maybe others.
post #6 of 14
Quote:
Originally posted by SENOR4Q
HIRSCH

How about NOS 12AX7 RCA Blackplates. I just bought a pair for my jolida jd100. I have not heard them yet but wanted to know your opinion on those and maybe others.
I'll have to see if I've got those. I've tried a related tube, RCA 7025 black plate, in my Cary LPP-1 phono amp, but it wasn't a happy pairing. That was a gain issue with my cartridge though, and probably not reflective of the tube.

There are people here who have a lot more experience with 12AX7's than I do.
post #7 of 14
Thread Starter 
Thanks for the answers fellows. I forgot to ask a related question though. When is it that tubes die? Do they go out like a light bulb? I've had one EL34 which got dim and then just ceased to work over the coarse of a few days or so. Is this typical? Or is there some gradual performance decrease?
post #8 of 14
Maybe this is a stupid question, but how do we know the tube is not working anymore? Is it like light bulb?
post #9 of 14
The life of a human being best reflects the life a tube, as Mikial of singlepower said. Like a human, the tubes undergoes a steady progression in quality of performance until a plateau is reached, where the tube satays at for most of its life. In its later days it undergoes a steady decline in quality of performane until it finaly dies out or you get rid of it due to the noticable decline in performance.
post #10 of 14
Quote:
Originally posted by mkmelt

If you want your tubes to last as long as possible, running your amplifier all of the time is one way, although it wastes electricity and generates heat into your home, even when you are not listening.
This is an interesting comment. Based on the rest of the post, it is obvious mkmelt has knowledge and experience with tubes. In the years I have used and read about tubes, all the comments I have ever seen are to the contrary. That is you do not leave them on as it shortens the life of the tube, and it was always my impression from everything I have ever read that leaving them on all the time was a sure way to use them up much more quickly. Is there anything to back up the idea of leaving them on all the time when many experts (primarily on Audio Asylum, dealers I have trusted and bought from and Leonard at Audio Research) say not to do that?
post #11 of 14
The biggest stress on a tube is the power up/power off cycle. So, the more that the unit is turned on and off, the more repetitive stress the tube is under and the shorter its life will be. OTOH, tubes do have a finite life span, so leaving them on when not in use will also shorten the usable life. There is no right answer here. Nobody can say what the "right" way is. My own compromise is to turn tube gear on when I get home from work, if I'm going to use it that evening. It stays on all evening, and gets turned off when I go to bed. Only one power cycle per day, but only 1/3 the tube use if left on 24/7 (less for amps that won't get used daily). That doesn't mean that this is the best way. I don't think anybody knows that definitively.
post #12 of 14
That pretty much reflects my practice as well. Turn them on when I get home and turn on music and off when I finish and/or go to bed. My SS stuff (CDP and phono preamp) stay on 24/7 however. I have just never heard of leaving tubes on 24/7 to prolong their life.
post #13 of 14
I never meant to imply that leaving a tube component running 24x7 will extend the life of the components or the tubes. Assuming a properly operating tube amplifier or receiver, if you leave the component powered on all of the time, the tubes should reach or exceed their rated life. If you power the unit on and off several times a day, the life of the tubes and other components that are stressed during the voltage surge during startup will be shortened, by how much no one can say.

So if a given power tube, such as an EL34, is rated at 2500 hours life, after this many hours of operation most people would consider the tube's output to be reduced to the point of diminishing its function in an audio circuit. Unless the tube fails internally, where one of the grids can collapse and short out the cathode or the plate structure (rare but it does happen), or the vacuum seal is lost, the tube will continue to limp along in a weakened state for anywhere from several hundred to several thousand more hours. Many times, a tube that tests very weak and is many hundreds of hours past its expected life will still play and will sound every bit as musical as a stronger testing example. Although testing weak, such a tube can becapable of being used for audio applications, due to the transient nature of the music audio signals.

Heat is the one factor that shortens the life of all electronic components, including tubes. Anything you can do to keep get rid of the excess heat generated by the tubes, and other components, and keep the operating temperature down will extend the life of the tubes and the equipment.

If you set the bias of your output tubes higher than recommended, for those amplifiers that have adjustable bias, then they will draw more current when idling and will run hotter. This will shorten the life of the output tubes. If the maximum recommended bias is 50 milliamps per output tube, then don't set the bias current (or in the case of the Dynaco ST-70 amplifier, the 1.5 volt test point voltage equivalent used to indirectly measure and adjust the bias level) any higher than this if you want your tubes to last. Reducing the bias, by 10-15%, will lower the idling current of the tubes and the temperature, while maintaining the desired musical sound quality of the tubes during operation.

If you are using a vintage amplifier or receiver, and take care to see that the line voltage seen by the power supply is no higher than 110 volts, the entire amplifier will run cooler. 108-115Volts AC was the norm when these components were designed. Today. the AC line voltage frequenltly exceeds 123 volts, at least at my house.

Use a small 3 or 4 inch fan to blow air across the power tubes, and through the chassis. The operating temperature of the amplifier will be greatly lowered, and the tubes and all of the components will last much longer. For power tubes, figure on more than doubling the expected life of the tube if you provide additional ventilation cooling via a fan.
post #14 of 14
Thread Starter 
Who knows how many times I've turned on and off in 1 day when I was comparing power cords. But it's a necessary sacrifice I think because I hear power cord differences. I guess I'll stock some tubes since mine are on like 12-18 hours a day.
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