by Peter W. Wed Jul 24, 2019 3:18 pm
Mpffffff.... Opinion and Speculation follows at no particular level or relative mix:
I keep a very good, properly calibrated tube tester (Hickok 539B) that with additional tools (VOMs) may be used to match tubes. I also have the various updates and charts to support it, as well as some graded calibration tubes. Having this tool allows me to make some fairly accurate tests, including power tubes.
Were I to purchase new tubes, I would test them and record the results. I would leave them in the tester for a minimum of 30 minutes, each (yes, the tester will sustain that) so a to get accurate results. Whereupon I could re-test in the future against those results and observe any changes shown. Which I could then correlate to what I am hearing, or what I think I am hearing. Put another way, I would have an independently verifiable source of data.
Now, 1,000 hours of use on a tube, even an output tube driven fairly hard *should* be negligible. I have put about 1,200 hours on my office system that started with very well-used tubes in the first place. But, 1,000 hours is a long time between cleaning sockets and re-making connections.
You understand that what you hear is a function in five variables, only three of which are under your control, being: Source/Amplification/Speakers/Health/State-of-Ears. You have control over the first three, and experience, but do not fully control the last two. Your health controls your attitude. The state of your ears will be affected by the weather, what you have been doing the last 12 hours or so, even whether you have ridden in a high-speed elevator in the last 12 hours as a single example. And listener-fatigue is very, very real.
Now, rectifiers make DC current from AC current, which is then filtered and otherwise massaged by your amplifier's power supply. Under the presumption that you are getting the correct B+ levels, and there is no remaining significant AC component in it, that power-supply is rather catholic when it comes to the source of DC current, and will use it 'all the same'. For those who would challenge this contention - let's endeavor to set up a proper double-blind test and see what develops. Short of that, opinions rule, either way.
Source: If you use vinyl, the wear factor is both real and significant. Keep in mind that the typical stylus puts pressure on records at something approaching eight ( 8 ) pounds per square inch, and moving something like nine (9) miles per hour all the while being slammed from side-to-side at up to 20,000 times per second. A lot of energy is being transmitted into the grooves. And, vinyl being an imperfect plastic, it cannot take this sort of abuse more than about once per 24 hours without extensive damage, and will show real (and audible) wear, probably around the 10th playing anyway.
Similarly with various forms of tape, but with an absolute life, but more playback resilience.
So, if nothing has changed in your system and your sources are not suspect in any way, then it would not hurt for you to purchase replacement tubes to the proper configuration you desire. But before doing any of that, clean your tube sockets and pins (carefully, of course), re-make all your connections (speakers and sources), and clean everything along the signal path. No Joy? Try some tubes. But!! Replace them in categories - better yet, have someone else change them (or not) and see if you perceive a difference.
Tubes do certainly wear. And post-blight tubes much more so. But they are not cheap, and you need to be as sure as practical that you are not mis-identifying your perceptions or their sources.
Good luck with it!