Should an audio system be left on at all times?

Almarg - I'm not clear on reliability and you can probably tell me where I'm making mistake but if we take device like transistor that eventually fails (everything fails) - let say in 100 years then using 1 milion of them would cause earlier failure, and in case of 1 billion of them one would fail every hour - am I right so far?

Now I have pencil on the desk in front of me. It doesn't last forever and will eventually rot - let say in 100 years (used or not). So if I take 1 milion of similar pencils one would rot in an hour after it was manufactured?

Doesn't reilability engineering assume that there might be some (very rare) faulty components (or connections)?

People believe in proportionality and therefore everything has to fail some time but for instance life of steel under stress is infinity of cycles (no fatigue) as long as strees is below certain level (not true for stainless steel and other metals).

Imagine basketball with a rope around it. Add 1m (3 feet) to it and rope will be loose by about foot everywhere (radius increases by 1 foot). Now do the same with our earth around equador, add 1 meter and you'l get axactly same result - gap of 1 foot everywhere around the earth.
r2-r1=(L+1)/2pi - L/2pi = 1/2pi L disappeared. It is very strange and counter intuitive but has certain practical implications. For instance clothing sizes for children cannot be in the same numbering scheme/scale as for adults.

Kijanki -- Good questions.

I don't want to get into non-electronic things, because I'm not particularly knowledgeable about them.

But consider a transistor or integrated circuit. Envision a plot of failure rate vs. component age, based on the assumption that it is being operated within its specifications (not always the case). A plot of failure rate vs. age will start out at some relatively high value (infant mortality), which in turn will depend on the degree of screening, burn-in, quality control, etc. (which is better for military gear than for consumer gear -- one reason consumer gear is so much cheaper). The curve will then go down to a lower level following the infancy period, and remain relatively constant until old age, when it will rise considerably.

What is most relevant to the questions we have been discussing is the middle period, where the failure rate is lowest, and is fairly constant over a considerable number of years (as you have pointed out). If we consider only that period, where the failure rate is essentially constant, then yes, if that failure rate at that point on the age curve is, say one failure per 100 years, and we have 100 components of that type, then we can expect one of those components to fail each year, on average. One set of 100 components may do better than average, and last 5 years without a single failure. Another set of 100 components may do worse than average, and have a failure within a month. But averaged across a large number of sets of 100 components, there will be 1 failure per year per set, based on the assumptions of constant linear failure rate, mtbf of 100 years, and 100 components.

If the failure rate vs. age curve is not linear and constant, such as during infancy and old age, the analysis is more complex. And as I indicated earlier, calculation of system mtbf has to take into account and properly weight the mtbf's of the different types of components, as well as their relative quantities in the system.

Hope that clarifies things more than it confuses them!

Regards,
-- Al

Aw shucks--where is Sean when we need him....?

My system consists of a solid state cdp, solid state amps, and a tube preamp. I usually end up listening to music almost every night when I get home. Is the general consensus that I should keep everything except the tube preamp on at all times due to the high frequency of usage? My tube preamp is actually from Odyssey and the guy from Odyssey said that his co-worker's tube in the same preamp has lasted a year and a half so far and that it has yet to be turned off.

The original questions was: "Should an audio system be left on at all times?" I think a more appropriate question would have been "Should an audio system be left on at all times to enhance performance during each listening event", or "Should an audio system be left on at all times to increase longevity"? Frankly, I don't really care about the latter.

For me, it is all about whether my system sounds good when I sit down to listen in the brief windows of time my current life affords. If leaving my source and amp on all the time in order to shorten warm-up period for listening is a valid concept, then I will do that. If not, then I am just wasting electricity. I did not buy this gear to have it sound less than optimal for a period of 30 minutes to several days each time I sit down to listen over many many years. If it breaks, I will replace it with something better.