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Tube life questions (LD MKIII)

post #1 of 6
7/5/09 at 2:53pm
Thread Starter 
Hey there,

A few questions about tube life & my LD MK III amp:

- any idea on the length of the power tubes' life? (The previous owner said they'd put about 200-250hrs on them, I've probably put about another 120hrs, at least)

- what about driver tube life? I'm using a pair of Mullard M8161s and have put about 60 or so hours on them

- also, if the amp is left on, but with no music being played ('phones still connected), does that wear out the tubes equal to when there's music being pumped through?

-what type of power tubes can I use to replace the stock ones?

- the reason I'm asking these questions is the sound of my Little Dot MK III seems to have thinned out and become a little harsh, less warm & cozy and less deep bass - is this due to the tubes wearing out, if so, which ones (ie power or driver?)

Any help or info anyone can offer would be greatly appreciated.

Thank you!
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post #2 of 6
7/5/09 at 3:25pm
I've had a 12ax7a in my dac since 1995.

Military rated tubes will last longer and have tighter tolerances. Average tube life for gain tubes will be 5000-10,000 hrs. Some are higher.

Power tubes will maybe not have the life of the gain tubes but still get 2-5000 hrs depending on how hard they are driven.

Consider tubes are still being sold on ebay that have been taken out of gear made in the 40-50s.
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post #3 of 6
7/5/09 at 5:05pm
You really have to look at how a tube is driven to determine its life. Some of the small signal tubes I have in my old radios have been going for 40-50 years. Power output tubes don't last that long, but it all depends on where the designer biased the tubes and how hard you run them.
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post #4 of 6
7/5/09 at 9:18pm
Those Mullard driver tubes will probably live longer than you will. (I would guess between 75,000 and 250,000 hours, depending mostly on heater voltage, external ambient temperature, and plate dissipation).

The 6N6 could last a very, very long time, or maybe only a couple thousand hours. This really depends on how hard the output stage is running them. Based on the size of the power transformer that is under the cover, I would guess they are not run hard. If you have the misfortune of getting your amp with Chinese 6N6's, I would probably throw them out the next time you see them. Expect less than 1000 hours out of them to be sure.
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post #5 of 6
7/7/09 at 1:27am
Thread Starter 
So it looks like my measly few hundred hours of use is nothing! That's great to know, I was always a bit paranoid about wearing 'em out too fast, warming up too long, etc.

The sound issues have disappeared - I think it was sinus-related.

Thanks for info, much appreciated.
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post #6 of 6
7/7/09 at 1:28am
Thread Starter 
Quote:
Originally Posted by TubeStack View Post

- also, if the amp is left on, but with no music being played ('phones still connected), does that wear out the tubes equal to when there's music being pumped through?
Any info regarding this question?
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