Lifespan of NOS telefunken 12AX7?

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.