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Listening for tube degradation

Hey, just wondering what specifically there is to listen for in regards to tube degradation. I don't have access to test equipment so I have to rely on my ear to determine if certain tubes are on their last legs. I've been able to notice a definite "scratching" or muddied sound whenever one or more of the tubes are in need of replacement. However, I find myself replacing ALL of the tubes since I can never pinpoint which exact tube or tubes needs replacing. Also, are there any visual cues to look for (ie.output tubes glowing brighter than others)? I have a 15W integrated tube amp that you can look at on my system page.
hitman_hifi

Showing 2 responses by aball

aball
2,016 posts
 
What I have noticed is that the sound does get a little muddy (or fuzzy) and you get less gain. This latter one is how I ended up confirming it - I had to turn the volume up higher for the same loudness. Since my preamp has a numerical volume display, this was easy to notice.

I have since bought a restored tube tester. It turns out all the tubes in my amp were worn out indeed. I am very happy being able to monitor tube performance other than with my ears because I want to keep the sound at peak performance and don't want to risk having a tube die on me and breaking something... Tubes can fail catastrophically if you use them too long. I have witnessed this first hand before.

Arthur
aball
2,016 posts
 
I bought a restored and calibrated Superior TV12. While I agree that a "bad" tube can sound good (I've had this happen several times), the part that worries me are leaks and shorts - and for that, a tube tester can test very well and reliably. But a tube with a low transconductance score means that it has spent a good part of its life and leaks won't be far behind. So the tester can be a good predictor as well. As for sound quality, I use my ears for that.

Now, do you really need a tube tester? Well, new production tubes are not as bad as some people like to say so if you have them powered up all the time, just replace them all once a year. But if you like playing with NOS and used tubes, or have many tubes in your system (I have 15 tubes in mine), then it is best to keep track of leaks so you don't end up with anything damaged.

Arthur
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