Lifespan of NOS telefunken 12AX7?

Had a 12ax7 in an audio research SP-14 that was on 24/7 for 10 years. Still tested good. Do not know the brand
Alan

9,326 hrs.

Of course some tubes are hardier than others, but the lifespan will be determined by the equipment and how it is used.

There has to be a range of useful hours for telefunken tubes somewhere......

I just had my hopes up that someone had seen an hour use figure stated by telefunken on an original box or maybe some manufacturers literature. I understand this varies greatly depending on how the tube is used. How many hours do you guys have on your phono stage tubes?

Alan- that is quite a surprise. I didn't think a tube could last that long. Interesting.

Andy

"Alan- that is quite a surprise. I didn't think a tube could last that long. Interesting."

Audio Research rated the tubes in their hybrid preamps to last 10,000 hours. However, I have never seen a tube manufacturer give their tubes a lifespan. It really depends on the application. That same tube that lasts 10,000 hours in the Audio Research preamp may only last 500 in another preamp.

thanks for the info Rrog and elizabeth.

I might call rogue audio on monday just to ask them some questions about the circuit design on the ares phono I am using. Maybe they can tell me about how much stress the tubes will be under.

Andy

As Rrog and Elizabeth inferred, it would depend upon the plate voltage (voltage difference between anode and cathode) and DC current being run through the tube. The product of those two parameters is "plate dissipation" in Watts. Look up a tube data sheet for a 12AX7. It will give you the max numbers for each of those 3 parameters. If the actual plate voltage, plate current, and plate dissipation (information which you would have to obtain from the manufacturer, if you don't know how to measure) are in the midrange of the recommended max values, then the life of the tube will more depend upon sample to sample variations within the tube itself.

I am surprised at the story about the SP14, because Audio Research was notorious for running their tubes very "hard". I guess that applied to the output tubes in their amplifier designs. The old Dual 50 and its variants used to blow output tubes all the time.

Hmm. The SP14 uses 6DJ8's not 12AX7's - could explain longer than normal life.

Sp-14 is a solid state line stage with hybrid phono using one 6DJ8. As I mentioned previously, Audio Research rated those tubes to last 10,000 hours and the original tubes were Chinese, however, sorted by ARC. All of those hybrid preamps were slow to warm up, but because of the long tube life you could leave it on 24/7 for the best sound and you would only have to replace the tube once a year.

Re the SP14: What I thought based on memory, but I was too lazy to look it up. The SP14 did not use 12AX7s at all, so the story if not relevant.

10,000 hours is not very long if you have to leave your phono stage on 24 hours a day but only listen for one or two.

I have used Telefunkens and Amperex Bugle Boys from Vintage Tube Services for many years in my LAMM LL2 pre amp (which uses both 12AX7's and 6DJ8's) and find that I can get 3 to 6 years at 2 hours per night before the sound deteriorates or goes microphonic to the point I want to change - depends on your ears and mine are not the best. Phono stages may require more frequent change but mine is SS.

I've had Tele 12ax7s in a Rogue Atlas for 4 years and they still test new. Rogue is very easy on small tubes.

that is good to know about the rogue atlas. I hope I can get at least 5 years of service out of my tubes as they are a bit pricey.