I am probably not the typical user. My system is on typically 12+ hours a day and more like 18 hours a day on weekends. What is the recommended tube life, in hours, for the BHK amps and preamps?
I could not find actual recommendations in the manual/online, and wonder what you guys think.
Thanks !
Joe
Small signal tubes last for thousands of hours, 10,000+, if not over driven. But we like to obsess over these things. I would replace them after three years or so if I ran them this much (eight hours/day at work with a two week vacation is 2,000 hours).
Thank you. The 10K rule, plus or minus is kind of what I was thinking. Obviously I’ll keep my ears on it and listen for problems as the hours roll up.
I have never had a small signal tube fail, nor lose its sound. I have replaced some after several years out of paranoia, but then keep them knowing they are still fine. 
The venerable 300B was used on the original trans-Atlantic cable and survived tens of thousands of continuous hours. As enthusiasts we worry too much.
The recommended swap-out time for my old AudioResearch LS-26 was 4000 hours, but that was for the 6H30 tube. YMMV. I had put in some Siemens/Tungsram PCC88 in my BHK 250, and after only 625 hours the system developed a ‘pop’ in the right channel whenever the unit was shut off. Replacing the tubes fixed that, so those didn’t last as long as I’d hoped.
I have been following this for a few days. While preamps using small tubes will run for years, depending on how they are implemented, they do wear out. Power tubes, not the real issue here, often have short life spans.
The thing is with preamp tubes, you may not notice the change, until you put in fresh tubes. And there are no general rules, some preamps run their tubes hard. There was one preamp that was notorious for tube issues, it went through 6922s very quickly. And when you get into NOS tubes, different years of production has produced different quality in tubes. Buying NOS from Upscale may be the safest place to buy true NOS. eBay may claim a tube to be NOS, but the tube may have been used. There are already reports of early failure, and additional hiss.
I have run 12AX7, 12AU7, 6CG7/6FQ7, and now 6H30. I am also much like the OP, my stereo is on 16-18 hours a day. I can put my current preamp in standby, the preamp that ran 6CG7 and my other that runs 12AU7, were/are left on 24 hours a day. No failures, but fresh tubes always sounded a little better after burnin.
I just replaced the 6H30s after 7500 hours, and will in the future aim for 5000 hours. 6H30s are considered super tubes with a history of use by the Russian military.
The only definitive answer, will be the one from BHK, as he knows how hard he is driving those tubes. Until you get that answer, be conservative, you can always keep the tubes you pulled as backups, available for troubleshooting, or to be used again, if finances are tight.
You spent $6000 on a preamp, even more for a power amp/s I would not follow the 10,000 hr with those components. Although that is just my opinion, I don’t claim to be an expert. I can tell you this, I found a little tube hiss acceptable when running a $2000 preamp, I would not in one costing $6000. My Conrad Johnson CT5, bought used, is dead silent, Audio Research preamps I have heard are dead silent. The new Reference from AR does cost twice what the BHK does, but my CT5 listed new for $6500, and I would have to hear it against the BHK, before I would be able to say which sounds better, but that silent CT5 was a huge step forward in my system.
I think you need to figure out how many hours you are putting on your tubes, and decide if replacing tubes every couple years at around 3000-5000 hours wouldn’t be prudent. And if you find a NOS tube that is superior in sound quality, buy three or four extra sets, as they may not be available in a few years, or the price will have skyrocketed. Want an example, you used to be able to buy NOS 6H30dr for around, I was told a $100 a pair, now if you can find a matched pair it’s a minimum of $250, and climbing. Fortunately they are making new ones. I just bought a cyroed matched pair from Cyroset for $94 with shipping. For currently made tubes check out Cyroset, I got great service and tubes that sound excellent.
I think it time for BHK to give his expert opinion on how many hours he recommends. That will be the only answer that is definitive.
Sorry for not answering this sooner. To be honest, I really don’t have any kind of recommended numerical number for hours elapsed before changing tubes. I have been running a pair of the Tungstram 7DJ8/PCC88 my Stereo 250 for about 6 months with perhaps a daily average of an hour/day. I am about to swap them out with a newer pair to see if the sound is any different or better. This is not a lot of hours - perhaps 180 hours. My best advice is to have a spare set of one’s favorite tubes and swap them in every so often to see if the sound improves or not. I will report back when I change mine out.
BHK said My best advice is to have a spare set of one's favorite tubes and swap them in every so often to see if the sound improves or not.Good idea.