2. amps-preamps
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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
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
lwerner
58 posts
 
I also never had the equipment (or the knowledge) but learned a way after I made Heath and Dynakits, take cover off the amp and let it warm up,do not touch any part of the amp (be sure the selector switch is set to Lp or extra/cd whatever you are using, volume up a bit) and tap the tubes with a pencil. This may not tell you how much life is left in a tube as a Tester would, but if any tube makes any noise comming from the speaker when you tap it, static, spitting, burping, harmonics etc, it is done for and should be replaced.
Len W
swampwalker's avatar
swampwalker
5,138 posts
 
Len W- not to be contrary, but what you are hearing is microphonics. Some tubes are microphonic when new, some are not. I don't know if this can also occur due to aging. It may be sign that the tube needs to be replaced, but it is NOT a reliable indication of aging. BTW, some microphonic tubes can benefit greatly from a tube damper.
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