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Tube Life

I’m using a phono pre-amp with a pair of telefunken 12AX7 and one 12AT7. I purchased these tubes several years ago and they were rated at about 50% life. Are tube noise and tube rush the only reasons to change out tubes? Everything is silent and yet I can’t help but think that several years of use should indicate some sort of wear. Any experience or suggestions will be appreciated.
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ebm
9,311 posts
 
Depends on the voltage how high.DUDE!!
lewm
13,124 posts
 
Right, a tube rectifier helps to protect the downstream tubes from simultaneous application of filament and plate voltages. The plate voltages will come up slowly. Also the simple use of a thermistor in the filament transformer primaries will protect both the transformer and the tubes from rapid application of filament current. Most modern gear, even including tube gear, uses SS rectification and so does not afford the natural protection of a tube rectifier. However, it is a simple matter to employ a relay device that effects a time delay between application of filament voltage (first) and plate voltage (second).

I would not want to have to go hunting for ECC803S TFKs on an annual basis.
mapman's avatar
mapman
22,316 posts
 
Having an extra reference set to compare to is the best way to know for sure how another set is performing.

Or else you might just trust your ears enough to detect a problem that matters when it sneeks in.
dhcod
710 posts
 
I have TFK 12ax7s in a lot of places and 50% could mean 10 more years depending on the circuit. Trust your ears and the poster above who said older tubes become sleepy I think is right with regard to phono stage tubes.
wrm57
1,049 posts
 
VAC recommends leaving their Signature-type preamps on 24/7 unless you're going to be away from the system for an extended period. That's what they do. I was told to expect to change tubes every 5 years using this regimen. Clearly, they expect a lot of tube life in their circuit. YMMV.
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