Tube Life Question: 12AX7 Drivers

Usual answer is 10,000 hours.

Hi Joe, 10,000 hours is the number i have heard.

I own a vintage Realistic (yes RAT SCHACK) Stereoline/40 tube integrated from the fifties and the 12AX7 drivers are original Realistic tubes. They still test «good» in my Hickok tube tester. How's that for longevity.

Trelja, 10,000 hours for NOS tubes. I have heard that family of Chinese 12AX7's, 12AU7's, and 12AT7's have a considerably shorter lifespan. The good news is that they are cheap, and have low noise, which makes them a good candidate in the phono section

Thanks for the responses!

Yes, the usual number is 2000 hours for output tubes, and 10000 hours for drivers and preamp tubes. But, I have often found conventional wisdom has little relevance in how things actually work. As Goldorak's experience shows, 10000 hours might be just some measuring stick that who knows came up with. I have heard others say this as well.

Personally, I've been lucky when it comes to tubes. I recently sold a pair of monos that had an appreciable number of hours on them, with the original output tubes. As the builder is a friend, he has made the point to me numerous times that he really is easy on the output tubes. When I tested the tubes, I realized just how easy he was talking about - they tested virtually new.

The reason I'm asking is that I recently came into an amplifier that is a lifetime purchase for me. And, I seem to have found the ideal 12AX7 driver tube. It's not new production or inexpensive, and I want to ensure that I have sufficient stock to last many, many years.

Hi Joe- 12AX7s can't make a lot of current, which usually means they get voltage amplifier service in a power amplifier. Using them as a driver tube is quite unusual. I take it the amp is Class A? That would be about the only type of service that a 12AX7 would work for.

Delayed B+ voltage on warmup will also help prolong the life of the tube. You might look into adding this feature if it is not already on the amp.

Depends on the tubes - I know the NOS RCA black plate tubes last about 5000 hours (input tubes) while others are supposed to last 2000 hours.

I'm honored by you checking in on this thread, Ralph! Been meaning to call you as it's been a while for us, but I wanted you to have a chance to reenergize after CES first...

The three Jadis amps I have owned all use 12AX7; the Orchestra Reference, DA30, and DA60. The JOR was Class A/B, the other two are Class A. I never rolled the 12AX7 in the JOR, but my experience with the DA60 has proven it has quite an effect on the sonics. The DA30 was not so pronounced.

As usual, you are most perceptive. The amp in question, the DA60, does have the Standby/Operate feature, as does my M60 monos. And, from the experience with my Atmas, I generally power up, wait 1 - 3 minutes, then switch to operate. Not sure if it makes a difference on shutdown, but I also find myself doing the reverse for what it's worth - which may be nada.

12AX7 driver tubes in my amp (SEP Class A circuit)5-6 mounths last (3-4 hours listening a day)they are EH 12AX7s
preamp tubes are 12AU7 and power tubes are KT88 and they last
atleast a year but driver tubes getting dull,dry and lifeless
in 6th mounth. I do not know why?

Ben, not to be a wiseguy, but you might want to check either the guy you're buying tubes from, the bias settings on that amp, or what the voltage coming out of the wall actually is. Honestly, you are seeing probably the worst tube life I've ever encountered.

Trelja,thanks for your help, my amp is auto bias, though voltage is not bad I use power regulator,the only logic reason
left is the tubes I have bought EH12AX7 s were bulk version and they might be terrible short life,I will try to buy original box version.

Ben what you describe as dull.dry and lifeless others might perceive as burn in. Try the Sovtek LPS it might be right up your alley and are supposed to be quite rugged.