Koestner,
I want to say upfront that I have no formal training in electronics and my comments are based solely from my personal experience with one tubed preamp, a VTL 2.5 that I bought new in the Spring of 2006. I had an Aragon 4004 amp at the time, paired with an Adcom GFP-565 solid state preamp, and I was looking for a more dimensional and 'in the room' type of presentation. I had borrowed a local dealer's demo unit for a few months, with the stock Russian or Chinese tubes, verifying that this preamp gave me the presentation I wanted before ordering a new unit along with a pair each of 12au7 and 12at7 NOS Mullard tubes from Upscale Audio.
I received the new unit in mid May 2006 and immediately replaced the stock tubes with the Mullards. I was completely new to tubed preamps at the time and had read many forums debating whether to leave tube preamps on 24/7 or to turn them off after each use. At the time I wanted my $160 worth of tubes to last as long as possible, so I mistakenly reasoned that less total 'on' time would allow the tubes to last longer. Therefore, I initially turned the preamp off after each listening.
However, I quickly and clearly noticed that the tubes sounded significantly better after they had been on for awhile; the longer they played (both during each listening session and in total hours played) the better they performed. I also was weary of waiting for the tubes to warm up and sound their best from a cold startup. About this time, I read several forum posts from tube preamp users claiming that switching vacuum tubes on/off was more detrimental to tube life than leaving them on 24/7 and avoiding the repeated surges of electricity caused by powering on. This theory struck me as being counterintuitive but, at the same time, very intriguing and worthy of testing.
So, about the end of May, I began leaving my preamp on 24/7. This was very convenient and my music sounded great from the first track through the last. The only possible downside was the anticipated shortening of tube life. But my system was sounding so good I just chalked this up to the cost of having a very good sounding system.
To make a long story a bit shorter, I'll fast forward 6 1/2 years to January, 2013: my system still sounded good except I noticed a bit of thinness, lack of dimension and that 'in the room' quality to the sound that I enjoyed so much earlier. There was also an odd sameness to the acoustic perspective no matter what track was played; the sonic illusion being centered on the stage and about 20-30 feet back. So, I replaced the 4 NOS Mullards with a fresh set ($200 total cost, just $40 more than my originals that were $160 total almost 7 years earlier) and everything lacking was restored and the sonic illusion presented was unique again on each recording.
I related my experience because I thought it's relevant to your stated concern and demonstrates why I would suggest that 12au7 tubes lose less life at idle than when playing music and would recommend leaving the tubes on 24/7. I think 6 1/2 year tube life would be considered more than acceptable by most owners.
However, I think it's important to realize this is just one person's experience with one preamp and one brand of tubes. It is likely a bit risky to generalize from such a limited sample size. Results may vary not only by preamp and tube brand, but by more specific variables such as tube type and between manufacturing dates and sites and even between same date batches of the same brand and tube type produced at the same sites/plants.
No matter which method you choose, tubes do have a finite life and will eventually require replacement. If you don't have an expensive tube tester or access to one, small preamp tubes degrade so gradually that you'll need to either remain acutely aware of subtle sound degradation and changes as the tubes age or just wait until you notice them eventually to determine when the tubes need to be replaced.
I now realize that a thinning of the sound, lessening of 3d imaging and a similar sonic perspective on various tracks can all be considered signs of tube aging and result in a degradation in performance. I would suggest it may be simpler to just change tubes after a given amount of time or hours of usage rather than trying to discern the point in time that you notice these somewhat subtle sonic changes. This method also allows you the freedom to relax and just enjoy your music.
Hope this helped,
Tim
I want to say upfront that I have no formal training in electronics and my comments are based solely from my personal experience with one tubed preamp, a VTL 2.5 that I bought new in the Spring of 2006. I had an Aragon 4004 amp at the time, paired with an Adcom GFP-565 solid state preamp, and I was looking for a more dimensional and 'in the room' type of presentation. I had borrowed a local dealer's demo unit for a few months, with the stock Russian or Chinese tubes, verifying that this preamp gave me the presentation I wanted before ordering a new unit along with a pair each of 12au7 and 12at7 NOS Mullard tubes from Upscale Audio.
I received the new unit in mid May 2006 and immediately replaced the stock tubes with the Mullards. I was completely new to tubed preamps at the time and had read many forums debating whether to leave tube preamps on 24/7 or to turn them off after each use. At the time I wanted my $160 worth of tubes to last as long as possible, so I mistakenly reasoned that less total 'on' time would allow the tubes to last longer. Therefore, I initially turned the preamp off after each listening.
However, I quickly and clearly noticed that the tubes sounded significantly better after they had been on for awhile; the longer they played (both during each listening session and in total hours played) the better they performed. I also was weary of waiting for the tubes to warm up and sound their best from a cold startup. About this time, I read several forum posts from tube preamp users claiming that switching vacuum tubes on/off was more detrimental to tube life than leaving them on 24/7 and avoiding the repeated surges of electricity caused by powering on. This theory struck me as being counterintuitive but, at the same time, very intriguing and worthy of testing.
So, about the end of May, I began leaving my preamp on 24/7. This was very convenient and my music sounded great from the first track through the last. The only possible downside was the anticipated shortening of tube life. But my system was sounding so good I just chalked this up to the cost of having a very good sounding system.
To make a long story a bit shorter, I'll fast forward 6 1/2 years to January, 2013: my system still sounded good except I noticed a bit of thinness, lack of dimension and that 'in the room' quality to the sound that I enjoyed so much earlier. There was also an odd sameness to the acoustic perspective no matter what track was played; the sonic illusion being centered on the stage and about 20-30 feet back. So, I replaced the 4 NOS Mullards with a fresh set ($200 total cost, just $40 more than my originals that were $160 total almost 7 years earlier) and everything lacking was restored and the sonic illusion presented was unique again on each recording.
I related my experience because I thought it's relevant to your stated concern and demonstrates why I would suggest that 12au7 tubes lose less life at idle than when playing music and would recommend leaving the tubes on 24/7. I think 6 1/2 year tube life would be considered more than acceptable by most owners.
However, I think it's important to realize this is just one person's experience with one preamp and one brand of tubes. It is likely a bit risky to generalize from such a limited sample size. Results may vary not only by preamp and tube brand, but by more specific variables such as tube type and between manufacturing dates and sites and even between same date batches of the same brand and tube type produced at the same sites/plants.
No matter which method you choose, tubes do have a finite life and will eventually require replacement. If you don't have an expensive tube tester or access to one, small preamp tubes degrade so gradually that you'll need to either remain acutely aware of subtle sound degradation and changes as the tubes age or just wait until you notice them eventually to determine when the tubes need to be replaced.
I now realize that a thinning of the sound, lessening of 3d imaging and a similar sonic perspective on various tracks can all be considered signs of tube aging and result in a degradation in performance. I would suggest it may be simpler to just change tubes after a given amount of time or hours of usage rather than trying to discern the point in time that you notice these somewhat subtle sonic changes. This method also allows you the freedom to relax and just enjoy your music.
Hope this helped,
Tim