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Yes, I'd like someone with a book (what a scary thought...) or better yet with professional experience to give his opinions on the topic.
I'm not sure you will find people more knowledgeable about such things than Hirsch and Jamato, but if you want to ask your question to another group of tube-heads, you can try Tubes Asylum
I suggest that if you do decide to post over there that you be extremely polite if you actually want people to reply
Unfortunately none of those mentioned by you actually had a clear and on topic reply, that's why I asked for more opinions.
Thanks for the link, I'll probably post there eventually.
Originally Posted by nick20
However, most everything from Google, came from a book, eventually. How do you think it got there?
Don't get me wrong, that's still extremely hilarious, but it's great you didn't say everything in books eventually came from Google
For my benefit at least, could you please re-state exactly what your question is?
See, now that's already a bit unpolite, making me ask for the third or fourth time
However, I would like to know manufacturer declared (and/or actual, if there are none of the first) hours of functioning for 40s-50s 6SN7 tubes, esp. military versions (VT-231, etc.). Assuming normal operating conditions as stated by the producer.
I was also interested in less than obvious factors that can influence the life-span of those tubes - and general audio performance, actually - such as operating points, regimes, type of powering etc. I would welcome a good resource on this, online or not, as it is a wide and complex subject.
I certainly wasn't trying to be impolite - in fact, I was trying to help.
The RCA Datasheet for the 6SN7 does not spec any life expectancy, although it certainly does spec standard operating conditions: http://www.tubezone.net/pdf/6sn7.pdf
And if the makers do not provide a spec for lifespan, I'm not sure that you will ever get a definitive answer to your question - all you will get is anecdotal evidence. I searched tubes asylum, and there was nothing definitive there except the suggestion to check the RCA tube manual, which I was able to find online, but which says nothing about lifespan. Even if they did, all the could provide was a Mean Time Before Failure (MTBF), which is, of course, a MEAN
5000-7000 hours does sound a bit optimistic, from what I've heard it could be perhaps half of that; however it all depends on what the figure means: is it the degradation of it's response below certain values or total lifetime until failure.
Even though the manufacturers may not have usually provided life expectancies for the tubes, they could have done so for the military versions - in which case they may lay somewhere in an army manual or spec.
However, the best advice would indeed come from a professional who has worked with this tube and knows it's limitations.
But you see, whenever we get into serious territory and someone brings a significant issue to the table - one which may involve hard gained knowledge or even trade secrets - all the 'gurus' suddenly have something else to do and you're left with Google
Last edited by Von Soundcard; 07-09-2008 at 07:05 AM..
5000-7000 hours does sound a bit optimistic, from what I've heard it could be perhaps half of that; however it all depends on what the figure means: is it the degradation of it's response below certain values or total lifetime until failure.
Even though the manufacturers may not have usually provided life expectancies for the tubes, they could have done so for the military versions - in which case they may lay somewhere in an army manual or spec.
However, the best advice would indeed come from a professional who has worked with this tube and knows it's limitations.
But you see, whenever we get into serious territory and someone brings a significant issue to the table - one which may involve hard gained knowledge or even trade secrets - all the 'gurus' suddenly have something else to do and you're left with Google
I understand the importance of answering your question, but you will get mixed results.
You have to remember these tubes are up to 60 years old, and may have never been used. It could die on you the next day you have it. And because of the nature of tubes, we kind of average what the well respected have to say, and get from 1,000-8,000 hours. Since they are so old, there is no concrete evidence saying one tube WILL last "X" amount of hours. My advise to you, buy multiple replacements, that way you will always have one hand.
You could have 10 of the same tubes, with 4 failing under 1,000 hours,4 failing between 2,000 and 6,000, and you may find the rest of your tubes average 7,000+ hours.
It is too dependent on the source, and the tube. I don't know how much more you want. Dare I say to use Google, but I bet I can help you out with specifics, but it would be with the use of Google, which it seems your not to fond of.
And ask away. Some of those guys are true tube nuts; if you can't pull the answer you're looking for, you may not ever know. These are some of the most knowledgeable people in the Tubes department, I know.
The other real issue is this: let's say you were to discover that RCA spec'd the 6SN7 at 3,000 hours MTBF. What good does that information actually do you? That spec would be for a certain usage, which is almost certainly not going to match the actual usage you get in an amp anyway! So to me, the information you are seeking, while it may indeed be interesting academically, has almost no practical value.
And also, specs for tubes provided when they were made would not apply anyway to tubes that have been sitting on shelves for 50 years or so. These tubes clearly have aged, even if not used.
Bottom line: I don't think there is any information out there that will provide any real value. 6SN7's in audio amps could last for 30,000 hours potentially. But what is likely to happen to NOS tubes is that they will fail on power up at some point. Not the end of the world - just time to upgrade
That is a hollow consumerist and atechnical viewpoint
You should know how long your gear lasts - along with how you can make it last longer and perform better. If an amp is made to obey all limitations layed by the producer there is no reason the tube will die sooner. I'm not at all sure age plays such a large role in top quality tubes, and if it does is should be easily quantifiable by an expert.
The other thing is you can sometimes find very hard some tubes you like. Change is not always the best thing - if it's not broke why would you mess with it ? So you need to know well in advance how large a stock of your favorite tubes to make.
The best estimate of the actual life-span should come from a professional electronics engineer who has worked with these exact tubes - old NOS 6SN7 - and therefore knows exactly how they behave over time (which is what I've asked for all along). A general life expectancy figure from the manufacturer helps too.
