Average life of an OT?

Is there any consensus regarding how much life one should expect for a set of new output tubes? As I posted in my other thread, one of my KT88s red plated last night. These were purchase from Jim McShane 3.5 years ago and up until last night have worked flawlessly. I ran them on average a couple of hours per day (some days 8 hours, some days 2 hours, some times not for several days even a couple of weeks at all).

I generally not mucked with them besides once or twice removing them to clean the contacts and sockets, so I'm assuming that the tube simply failed on its own accord.

Thanks

jsl1234 wrote:Is there any consensus regarding how much life one should expect for a set of new output tubes? As I posted in my other thread, one of my KT88s red plated last night. These were purchase from Jim McShane 3.5 years ago and up until last night have worked flawlessly. I ran them on average a couple of hours per day (some days 8 hours, some days 2 hours, some times not for several days even a couple of weeks at all).

I generally not mucked with them besides once or twice removing them to clean the contacts and sockets, so I'm assuming that the tube simply failed on its own accord.

Thanks

As for my limited experience i know that a quad of JJ 6550 lasted 3400h and was still usable when i decided to try some other tubes.
3000 - 5000h is the expected lifetime for power tubes.
The above hours was measure as i installed a hour meter in my amp to save some hard data.

Well this seemed like an appropriate place for a reply.  I bought my first VTA-120 kit from Bob around about the end of 2010 I think. It had/has SOVTEK KT88s.  This morning I was checking the bias (which I hardly ever do) and noticed one was zero.  Swapped OTs from back to front on the left side, and the zero followed the tube.  So there you go.  I got 11 years out of that tube (and the other 3 still going).  It was the filament.  Since the AMP is in a cage I didn't notice that tube was dark.  I guess it's time . Why hadn't I replaced before?  Well the AMP has simply been flawless for all those years and I didn't give it any thought.  And last year I had the AMP on my trusty HP-339A distortion analyzer, and it was performing like new. (I was actually testing the analyzer, not that amp).  I have 4 AMPs from Bob, and they are simply marvelous!!  Iv'e communicated with Bob on and off over the years, and about 9 years ago he suggested it might be time to change the tubes.  Now I have a reason even though class AB seems to be limping along.   Long live Dynaco!!!

jsl1234 wrote:Is there any consensus regarding how much life one should expect for a set of new output tubes? As I posted in my other thread, one of my KT88s red plated last night. These were purchase from Jim McShane 3.5 years ago and up until last night have worked flawlessly. I ran them on average a couple of hours per day (some days 8 hours, some days 2 hours, some times not for several days even a couple of weeks at all).

I generally not mucked with them besides once or twice removing them to clean the contacts and sockets, so I'm assuming that the tube simply failed on its own accord.

Thanks

It sounds like you used the tubes about 1000 hours per year or so. If that's the case then the tube lasted about 3500 hours. That's about right for a tube that isn't either babied or pushed real hard.

I don't know what amp these were in, but I hope that it had either some kind of autobias installed or was cathode biased. If the amp has adjustable bias it needs to be checked and adjusted if needed from time to time to get the best performance from the tube.

Jim McShane wrote:

jsl1234 wrote:Is there any consensus regarding how much life one should expect for a set of new output tubes? As I posted in my other thread, one of my KT88s red plated last night. These were purchase from Jim McShane 3.5 years ago and up until last night have worked flawlessly. I ran them on average a couple of hours per day (some days 8 hours, some days 2 hours, some times not for several days even a couple of weeks at all).

I generally not mucked with them besides once or twice removing them to clean the contacts and sockets, so I'm assuming that the tube simply failed on its own accord.

Thanks

It sounds like you used the tubes about 1000 hours per year or so. If that's the case then the tube lasted about 3500 hours. That's about right for a tube that isn't either babied or pushed real hard.

I don't know what amp these were in, but I hope that it had either some kind of autobias installed or was cathode biased. If the amp has adjustable bias it needs to be checked and adjusted if needed from time to time to get the best performance from the tube.

Hi, it was in my VTA 120 that Audio Bill wired. An auto bias board was added about the same time I installed the KT88s. BTW I also installed a set of driver tubes you sold me and they are still going strong. after the red plate of the KT88 I reinstalled the original 6550s and the unit has been running fine. Once the 6550s wear out I’ll be back for another set of KT88s.

jsl1234 wrote:Hi, it was in my VTA 120 that Audio Bill wired. An auto bias board was added about the same time I installed the KT88s. BTW I also installed a set of driver tubes you sold me and they are still going strong. after the red plate of the KT88 I reinstalled the original 6550s and the unit has been running fine. Once the 6550s wear out I’ll be back for another set of KT88s.

I'm glad to hear, thanks for the heads up! With the bias adjustment under control and the amp being a solid, stable performer - your tubes should live a normal life in the VAST majority of cases.