Tube Burn-In - Phono Preamp

Looking for some guidance on proper way to burn-in tubes. I'll be trying a few different brands of matched pairs of 12AX7 tubes in a Project Tubebox S2 Phono Preamp. Will leaving the preamp on without music playing for 5 days or so do the trick? Or must audio be playing during the tube burn-in process? The pre-amp itself has been in use for a long time, so I'm certain it's circuits, caps, etc are all set..

Thanks

 

Prior thread about this: How to properly break in 12AX7 tubes without taking a lifetime.

If it was me, I'd give each set one long side of a disc (30 minutes or so) and call them broken in after that. I certainly wouldn't wait a week.

 

I believe in tube burnin. If they are true NOS straight out of the box, they will need some time to open up. You should be able to tell in short order if you'll like the timbre of a tube.

IME, having the component powered up is enough to break-in tubes. Playing music is even better.

 

First of all, I'd personally never leave any tube gear on and running unattended for days or even hours. Sure, unlikely to be a problem with preamp tubes, and I've done it accidentally without incident sometimes, but I've seen too many catastrophic and spectacular tube failures over the years to think that that's a safe practice.

Second, mine might be a minority opinion here, but I say all you're really doing is wasting tube life. Tubes reach thermal stability in 5, 10, 15 minute after turn on, and, after an initial period where you might burn them in at voltage to check for early failures and noise -- a QC practice that really should be done at the factory but isn't anymore, but is often done by a good retailer -- all that's going on from that point forward is the tube performance is slowly but inexorably declining in terms of transconductance, noise, heat stress, and in those twin triodes in triode matching. Tubes only get worse with use, not better. And if you're exposing caps and resistors to tube heat unnecessarily, because you're not listening to music, you're probably not doing them any favors in terms of operating life either. Third, just heating 'em up is pretty different from passing signal through 'em. If you're going to run 'em, might as well do it listening to music, especially while they're fresh and at their best.

 

Long-time tube user. Tube burn-in is a myth. Turn them on and they'll sound their best in about 30 min. No need to waste dozens or even hundreds of hours of their life cycle with that BS.

Think I'm wrong? Order two pairs. Use one for a month, swap it for the new one, but let it warm up for 1/2h before playing anything and tell me with a straight face the old ones sound convincingly better.

 

I know this won't convince you that burnin is real and this is not my intent.
I recently purchased two pairs of near NOS tested Ken Rad JAN VT-231 black glass since they are becoming scarce. Played one pair in my amp through burnin and beyond (3 weeks), then realised I should check the other pair for defects while they're under warranty. Installed them and there was a very different sound from the amp, lacking dynamics and soundstage. There was no deep bass that KR's are known for. Played them for a few hours, no defects, so put the originals back in the next day. Sounded wonderful.

 

Lots of possible reasons for that. I'd have to see the internals of those tubes to see if they differ from the good ones, I'd have to test them myself on a calibrated tube tester, etc. My guess is they were either not from the same production year, different tubes, or the bad ones were far from being NOS. I'd be curious to know the source you bought the bad ones from.

 

I didn't receive any bad tubes, I don't know what you mean.

Both pairs were matched for Gm, emissions, & structure by the dealer and came from a bulk tube box.
Pair #1... matching date codes of "T4", late 1944.
Pair #2..."P4" and "N4", 6 weeks apart in mid 1944.

That is all, I'm not going to debate this.

 

To spell it out, the tubes could have been aged a whole lot more than what was advertised, the tube tester could have been defective or not well calibrated either. The dealer is also not being revealed. If you want to be utterly sure about this, perform the test with current production tubes so you can be 100% sure of them being perfectly new and factory-matched.

The way you closed your last reply tells me all I need to know. It's a religion and you're putting faith into one anecdote when I have a decades of experience with tubes, especially 12AX7s which are being discussed here. Good luck with that.

 

Let me clarify this statement. Pair #2 upon installation had the same timbre and tonal qualities as Pair #1. It did not present a 3D soundstage yet and bass and highs were soft. Bass became more extended over the course of a 6 to 8 hour listening session.
I know how to listen, having worked at a mixing console for many years.

 

Don't be so offended, I'm only adding some anecdotal evidence of burnin to the thread. I'm not going to put the dealers name out here. None of my go to dealers had these Ken Rads in stock and haven't for months. I purchased from a large volume vender on Ebay. I did a test purchase from him a few months ago, when these rare tubes came up for sale, I was comfortable buying from him. And I asked him questions offline about his testing, uses a calibrated tester, I forget which one.

 

The wrong word is being used. "Puzzled" is more like it. "Offended" is a word I'd use to describe someone who puts an end to a valid sincere follow-up question with "That is all, I'm not going to debate this".

 

Your tone seemed more like anger than being puzzled. I'm not going to debate whether burnin is real is what I should have written. Sorry about that. You and I have different views on this subject and that's ok with me.

 

You got anger instead of an inquisitive tone from this???

"Lots of possible reasons for that. I'd have to see the internals of those tubes to see if they differ from the good ones, I'd have to test them myself on a calibrated tube tester, etc. My guess is they were either not from the same production year, different tubes, or the bad ones were far from being NOS. I'd be curious to know the source you bought the bad ones from."

That is even more puzzling.

Yes, we have different opinions which is OK but if you're unwilling to perform the aforementioned test with current production tube, you'll never confirm my verified conclusion is correct. Regardless, it's all good.

 

From this comment I was anticipating an audiophile feud which happens all too often. Nobody here is mean-spirited but a thread can sometimes become very heated. I've been attacked on the other large forum for stating my opinion. Again, I'm sorry for my miscue about debating the concept of burnin. I feel that's where this discussion went sideways.

 

It's all good. IMHO, we should all express our opinions without risking being insulted for it. You did nothing wrong by stating what you believe regardless of the fact we disagree on the topic.

 

two points-
1 burn in depends on tube. some tubes are close to their best sound after 25 hrs or so e.g. new tung sol, some take a few hundred e.g. new jj. regardless just sit back and listen.
2 my experience with the tube box DS. stock tung sol sounded the best overall and i tried nearly every new and NOS tube. for your reference in case you wind up in a big tube rabbit hole.