New Tube Burn in

Dan Beller-McKenna · From: Durham, New Hampshire, USA

Hi all,

I just put some new 6l6gcs in my Peavey Heritage. Do these need to be broken (burned) in before I start playing? They were sold as a matched quad, so I assume they got some breaking in for that process. I have the amp on standby; no smell, all glowing nicely.

Any advice appreciated.

Dan

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Dan Beller-McKenna
Durham, NH

Jack Stoner · From: Kansas City, MO

No, there is no "burn in" with tubes. Install them and go at it.

Some amps have a power amp Bias adjustment (e.g. the Fender's) and that really should be done, but even that is not an absolute.

Stephen Gambrell · From: Over there

I bought a new Fender Blues Deluxe, and it sounded eal distorted right out of the box. I turned the amp on full blast (no guitar plugged in, though---gotta think of the neighbors) and took my wife to dinner. We got home and I tried the amp again, and it had cleaned up nicely. I'm not sure if the tube burn-in was what fixed the problem, but the amp sure sounded a lot better afterwards.

Dan Beller-McKenna · From: Durham, New Hampshire, USA

Okay,
thanks guys. As soon as my sister-in-law and nephew leave and my wife goes out to the opera I'm gonna let 'er rip!!

Dan

Keith Cordell · From: San Diego

Power tubes do require a little burn in time sometimes. I usually do what was suggested above, just leave it on for a couple hours. It helps.

Jack Stoner · From: Kansas City, MO

Where do all these theories come from? I come from the era where all there were was tubes. I've been in electronics since 1955. There was never a "burn in" period, and that wasn't even thought about back then. Everything worked fine, as it was designed to do. If a tube went bad you replaced it or in the case of push pull amp, the pair (or pairs) were (sometimes) replaced.

I've had formal electronics training (again in the "tube era") and that was never brought up. My ARRL handbook does not have anything about it. I don't recall anything about tube burn in, in the RCA Tube manuals, etc.

Stephen Gambrell · From: Over there

Jack, I'm an old tube man myself, and the only tubes I recall ever actually "burning-in" were klystrons and magnetrons, back in the old microwave/HF days. As far as audio tubes, Iwas never formally told to let ANY tubes "burn in." I may have re-heated a cold solder joint, or something like that---But I swear, the amp sounded better after a couple of hours with the high voltage on.

Donny Hinson · From: Glen Burnie, Md. U.S.A.

No, tubes don't require any "burn in". A tube's performance starts to go down from the moment you start using it, due to degradation of the coating that's put on the cathode to aid in electron emission. With each use, the coating's thickness and effectivity declines, resulting in a loss of gain. When a tube fails an "emission test" (the most basic test of a tube's performance), it's because a large portion of that coating is gone.

However, that said, some amps might sound better (but not louder) in certain applications because of "weak tubes". It all depends on the sound you're looking for.

[This message was edited by Donny Hinson on 08 April 2006 at 06:20 PM.]

Brad Sarno · From: St. Louis, MO USA

I've found that although tubes are rearing and ready to go right out of the box, they do what I call "settle in" over the first couple week of use. A brand new tube has a kind of crisp and clean quality that sounds a bit bright compared to what the tube sounds like a few weeks later. But then after that period they seem to hold that smoother, broken-in sound for a very long time before they start to "go" which can also be a long and gradual process. I've never been able to fairly evaluate the sound of a tube when it's brand new, whether it's in a guitar amp, preamp, audiophile system, tube compressor, EQ, microphone, etc.

I've found in the instructions of numerous high end tube devices the strong recommendation to let the unit run for at least a week before real evaluation. I've observed the very same thing with the Black Boxes and the Rev Preamp. So I guess the thread here was asking if you need to "burn in" tubes. So no, you don't really need to do anything to make the tubes ready for use, but do know that the sound will improve significantly after a short period of time.

Also, although a tube is up and running usually within about 15 seconds of powering up, the inner structure of the tube's workings doesn't fully heat up and stabilize till after about 10-20 minutes. You can hear it if you listen.

Brad

[This message was edited by Brad Sarno on 09 April 2006 at 02:47 PM.]

Bobby Lee · From: Cloverdale, California, USA

When I was at Mesa/Boogie (over 20 years ago

) we always did an overnight burn before the final bench test.

Dave Mudgett · From: Central Pennsylvania and Gallatin, Tennessee

Back in the old days, people didn't push tube amps to the edge like players (especially lead guitar players) do nowadays. The sound of pushing them is one of the big differences between the older and more modern sounds - especially on guitar, of course. Here is where I notice the biggest differences between tubes, and also the effects of allowing the tube to warm up and burn in for a while. I agree that in the low-volume linear range of the tubes, this stuff doesn't make as much difference. But the way the tubes react to hard vs. soft picking attack, for example, may change, IMO.

Part of the effect of warmup is simply the tube heating up to full temperature. After a minute or so, it comes on, but it doesn't really reach full temperature. I believe that the full transient to equilibrium warmup is longer than people think. Then there's also the effect of everything in the amp warming up while playing due to tube heat, heat generated by the transformers, power resistors, and so on. All these heat variances affect the component values a little bit. If you're playing loud, those transformers can get hot - just reach in after a loud gig and feel them.

I concur exactly with Brad's comments. Try this - bias a set of tubes when you first put them in, and then run them for a while. Now check the bias again after they're fully warmed up and maybe a week or two later. I usually need to make a small adjustment - for a given tube type, there's a small range of quiescent plate current that I prefer to bias to, and that changes a bit for a while, in my experience. My Fenders have a bias meter built into a replacement back panel (the originals are tucked away), so checking bias is simply turning the meter on. I use a voltage regulator to stabilize the AC voltage so I get consistent readings. The bias definitely does drift while the amp fully warms up, and also for a few days or a week while the tube burns in.

What causes this? I'm not sure exactly, but my theory is 1) during warmup, the bias circuit may change, and 2) over several days, the bit of oxygen in the tube not removed when the tube bottle is evacuated is gobbled up while the tube burns in. According to this theory, after this happens, the tube is good to go until the mechanical structure and oxygen "getters" start to break down.

[This message was edited by Dave Mudgett on 09 April 2006 at 07:31 PM.]

Michael Holland · From: Nashville, Tennessee, USA

I've bought tubes from Triode Electronics and this is from their website.

quote:

Power tubes are tested and matched at typical operating voltages and dissipation, many also are burned in for 24 hours (where indicated) in some cases power tubes are burned in matched at the factory (eg: most JJ/Tesla product).

Jack Stoner · From: Kansas City, MO

"Burning in" at a factory production facility is a good QC function. It will help to find marginal components or ones that fail prematurely. When you purchase a new "whatever" you expect it to have been gone through QC testing for reliability.

As far as consumer "burn in", I still consider it a Myth. As with the QC burn in mentioned, I suspect all tubes are tested (burned in) at the factory as part of the QC process if the tube manufacturer wants any reliability. When I worked for a Jukebox and Background music company, the amps that they used (Bogen) had all the tubes go thorugh a QC process (24 hour acceptance test "burn in") to ensure the tubes met their technical requirements, reliability and to minimize failures before they were released to production - not so the tube would "sound better".

David Mason · From: Cambridge, MD, USA

It certainly sounds like people have gotten used to the sound of tubes being "right" when they're a little, tiny bit worn down or somewhat less than brand new - I feel the same way about strings and guitar picks, so why not?

Jim Sliff · From: Lawndale California, USA

i agree with Dave Mudgett - new production tubes DO need a burn-in followed by a bias check. Almost all European and Asian tubes will drift - matched sets rarely stay that way.

Less of a problem with NOS tubes, where quiality conrol during manufacturing was far superior.

Dave Mudgett · From: Central Pennsylvania and Gallatin, Tennessee

Certainly, burning in as a QC process on the whole amp is important. But I find that tubes do usually drift a lot more when new than after they burn in, and especially the bias often needs to be adjusted. To me, it's not a question of "the tube sounds intrinsically better", but that it's properly set up in the circuit. As I said above, I think this is more of an issue if the tube is being pushed hard.

I agree with Jim that this is much more of a problem with newly manufactured tubes than the good ole' NOS American-made tubes. This is not just me talking - look at this report that Ken Fox linked in a recent post:
http://www.vacuumtube.com/FAQ1.htm

They argue that modern production tubes are not pumped for vacuum very long, and don't pull a good hard vacuum. This is a serious problem, IMO. I believe this is one of the reasons modern tubes tend to drift more, and I have certainly noticed that.

Donny Hinson · From: Glen Burnie, Md. U.S.A.

"Burn-in" and "warm-up" are not the same thing!

Electronic devices are designed to operate at a specified temperature, and they will not exhibit maximum stability or performance until they reach that temperature. This is referred to as the "warm-up" time, and it occurs every time a device is powered up.

"Burning-in" a component or device is more of a quality control technique, and it uses an extended operating time (much longer than a "warm-up" period) to ensure a device will operate within it's design parameters over an extended term. It is generally not a method used to improve the operating specifications of any component, but rather a stress test that helps identify weak components or inferior designs.

However, for those of you who feel that "burned in" tubes sound better, I will gladly trade you some "burned-in" (AKA "used") American made tubes for some NOS American made tubes!

Any takers?

Brad Sarno · From: St. Louis, MO USA

Yes to all. Jack, I agree that they aren't doing a burn-in for sonic reasons, they're doing it for quality control reasons to see if the tube is gonna work or fail. I think there are a few things we're talking about here.

Burn-in at the factory is likely a QC thing to make sure the thing works and specs out ok.

Burn-in at an amp maker is a bit more of the same QC.

Break-in time has more to do with the time it takes for a tube to mellow out a bit after maybe a few weeks of useage where it settles in to the sound it'll have for a long while. This is just something the consumer gets to observe and experience. It's not any official process that manufacturers typically do. In my mastering business, I use both a Manley tube EQ and a Manley tube compressor. In this element, the audio is very much under the microscope and you can clearly hear these processes at work. When I retube these things, I'll leave them on 24/7 for about 4 or 5 days before I'll use them for mastering. If I do a session in that early period, there's no way I can go back and reproduce that sound because the tubes only sound that way for a few dozen hours. But once they've chilled out a bit, they seem to stay that way for at least a couple of years before I hear them going out. By the way, I still wonder if a Telefunken tube will go bad. They're a freak of nature. I've heard stories from studios who've had them on 24/7 for about 20 years and they're still going strong. My RCA's and GE's dont' quite hold up like that. And the new stuff can't even come close. Some of the new tubes do sound great, but they still don't make them like they used to.

And finally warm-up time is something that happens every time you turn the thing on. It may be on and running in 15 seconds, but it's really warmed up and stabilized after 10 or 20 minutes. I let my pro gear warm up for about a half hour before I use it. For guitar amps, it's really not a big issue unless it's for an important session.

I think we're all saying just about the same thing.

Brad

Michael Holland · From: Nashville, Tennessee, USA

Great thread, and since we're talking tube health I'd just like to mention the importance of the 'standby'. ALWAYS power up with the standby on. This allows the power tubes to warm up before they see current from the pre-amp and they will last alot, lot longer.

Dave Mudgett · From: Central Pennsylvania and Gallatin, Tennessee

So we now have three technical terms:

1. Warm-up

2. Burn-in

3. Break-in

OK, I'll buy that. Many tube people refer to 2. and 3. synonymously, but one can make a semantic distinction.

Yes, the standby switch is very important, especially when the amp has a solid-state rectifier. It often takes time for the bias voltage to build up. If the rectifier instantly puts 400-500 volts on the plates, the tube runs way hot, with huge plate current, until that negative bias voltage builds up to control the quiescent plate current. The standby switch allows you to wait to put plate voltage on the tubes until after the amp warms up and the bias voltage is steady.

BTW, Donny - yes, I would rather have two nice NOS power tubes matched after 20 hours burn-in than two of those same tubes matched with no burn-in period. In fact, the vendors I use do precisely that, and I believe it makes a significant difference.

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