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How do you know when to replace a tube?

I'm new to tubes. I have a Baby Sophia powering a pair of Klipsch Quartets from an AR ES-1 turntable. The sound is often warm and lovely but sometimes thin and metallic to the point of making me want to stop listening. Sometimes the first couple of songs on an album sound soft and sunny but the last songs sound flat and brassy. The tubes on this amp were the original tubes used by a previous owner; I've used them maybe an additional 50 hours total. Does the sound quality of a tubed amp gradually degrade or do the tubes simply stop working? Will certain types of music reveal a degraded tube or will it be pretty obvious with all kinds of music? Thanks for your responses. I want to get back to all warm and sunny sounds!
sumphull
herman
2,254 posts
 
.

They do gradually degrade but can also just quit working.

That would not be the problem with the sound changing from beginning to the end of the album. That can be caused by improper cartridge alignment.

I'm with the others; buy a new set of tubes and see if the sound improves.
sumphull OP
2 posts
 
Thank you all for your responses and helpful suggestions. I'll go ahead and replace the tubes. The cartridge alignment idea is really helpful and will give me another project to explore.
elevick
2,636 posts
 
I disagree with tube replacement. As said by Philjolet old tubes will get "boring", not bright. New tubes may actually make your system sound even worse, depending on what you buy.

2 things I can think of:
First-Klipsch can be fatiguing after a while. They may sound great at first but after 15-20 minutes your ears grow tired. These are really accurate and sometimes overly-revealing speakers.
Secondly-It could be your cartridge alignment. If the first half of every album sounds great but once the need approaches the halfway point or so on an album it may be tracking funny. THIS IS MY GUESS. Make sure your cartridge is properly set up by a pro.
bifwynne
2,206 posts
 
Elevick makes a fair comment. I agree with the adage "if it ain't broke, don't fix it." Sure, check the cartridge alignment.

However, I do caution that if the power tubes are old, they are susceptible to failure, which in some cases could take out bias resisters. I would still ask the prior owner the age of the tubes. If the hours exceed factory recommendations, I suggest replacement.

BTW, is the amp old?? There's a couple of threads running about cap failure, particularly electrolytics. Just a thought.

FWIW
rrog
1,958 posts
 
See if you get the same results with a different source like a CD player. If the same thing happens with CD's then it may be tubes. Tubes can change with temperature and not always for the better. However, when you own tube equipment it is always a good idea to have spare tubes on hand.
The other thing that comes to mind is your AC power. If everything else checks out ok you may want to try a power conditioner.
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