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Old 3rd Dec 2019, 12:40 pm   #1
David Simpson
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Default "Burning - in" Double Triodes

A Forum chap has a current "Wanted" thread for a 12AU7/ECC82. This seems to have created a debate on "Burning in" wee NOS double triodes. Perhaps this might even extend to valves in general.
Are not NOS ECC82's, like some other ECC valves, now becoming a bit expensive, as well as becoming more desirable by audio amp enthusiasts. Hence I'd be concerned as to how different folk attempt to burn-in such valves.
In my experience, all these wee ECC TT valves are not the most robust of valves, and need care when testing. Also, I don't recall AVO, in any of their VCM servicing manuals, demanding that CV455's/491's etc. are thoroughly burnt-in prior to being "Standardised".
Over the years, I've supplied a number of folk with S'd ECC valves, and non of them had requested or demanded that they be burnt-in. Also, for my own use & collection purposes I've kept several ECC valves, 81's, 82's, E88CC's, E288CC's, and so on, because they've given excellent Gm graph results. Occasionally, I'll re-check them, but haven't observed any Ia/Vg slope changes, despite them not having been burnt-in.
I have a Marconi TF995A/5 which contains TT valves, but there is nothing in the service manual about burning-in replacements. Likewise, many years ago used to service & repair TF801B's & CT452A's, etc., but don't remember any military spec for burning-in.
What does burning-in do - - re-align the thoriated tungsten molecules, finally get the getters to absorb the last remaining oxygen atom, what ?

Regards, David

Last edited by David Simpson; 3rd Dec 2019 at 12:41 pm. Reason: spelling
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Old 3rd Dec 2019, 1:04 pm   #2
stevehertz
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Default Re: "Burning - in" Double Triodes

I don't believe in the practise of burning in any electronic component wrt how it sounds ie supposedly better when 'burnt in'.

I'd like to see objective evidence of this if people are saying it happens. Otherwise we're into the normal round of audiophool comments such, "Well I burnt in my so and so and it sounded so much better afterwards." That kind of comment is purely subjective and unless coming from the likes of the late Angus McKenzie, generally worthless. And even if there is some evidence that the characteristics of components do change minutely following a burn in period, then personally I doubt very much if this is within audible limits.

They're not an electronic component so I'm within my statement above (!), but speakers will change (burn in) to some degree as result of their suspension becoming more compliant with use. But with modern materials even that is becoming less of an effect now.
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Old 3rd Dec 2019, 1:14 pm   #3
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Default Re: "Burning - in" Double Triodes

As Steve says, there's a strong whiff of audiophoolery about this. All sorts of audio equipment supposedly sounds much better after hours / days / weeks of use. It's not impossible, but I'd like to see some lab results or double blind comparisons.
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Old 3rd Dec 2019, 1:25 pm   #4
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Default Re: "Burning - in" Double Triodes

Possibly burn in is used to show up any premature failure.
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Old 3rd Dec 2019, 1:39 pm   #5
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Default Re: "Burning - in" Double Triodes

It would be instructive to know what was done in the days when computers might have thousands of double-triodes and other valves in and where there was a genuine need to overcome the infant mortality side of the bath-tub curve. It's understandable that the likes of Tektronix who were making expensive and complex reference-grade kit with dozens of valves in would see burn-in as a worthwhile investment in reputation safe-guarding. In the world of audiophoolery, it doesn't take long to spot the syndrome of perfectionism and loss of rational perspective, and the "I'm even more pedantic than you, therefore my dedication trumps yours" mindset. It's hardly surprising that burn-in has been taken up as another ritual on the path to true belief, quickly becoming a commandment.
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Old 3rd Dec 2019, 2:20 pm   #6
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Default Re: "Burning - in" Double Triodes

I thought that it was general knowledge that the characteristics of valves drift with age but especially in the first few hours of use, this being more pronounced the larger the amplification factor was?

Perhaps this shows up fact that (excluding audiophoolery) the requirements of amateur versus professional (especially military) users and uses of equipment using valves are somewhat less critical?

If the valve is to be used in a DC coupled circuit (say a piece of test gear such as an oscilloscope) then this drift can be tedious and annoying, requiring constant manual adjustment of 'offset controls' such as screen position or worse still in one of those old analog computers!

Also in AC circuits were two or more valves are in a balanced arrangement, say in an SSB mixer where imbalance causes carrier suppression to be degraded, unless regular balance control tweaking is acceptable to the user (definately against the rules for military kit! "hang on a minute sarge, just got to find a screwdriver to tweak the set before I can relay that message to HQ")

And once again as has already been mentioned, burning in was almost essential for professional/military kit to remove infant mortality problems.

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Old 3rd Dec 2019, 2:27 pm   #7
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Default Re: "Burning - in" Double Triodes

I think the answer to this dilemma has already been alluded to.

In AC coupled amplifiers it would frankly be a waste of time and valve life to bother doing it. You might weed out an occasional dud valve, but so what, they weed themselves out anyway at a rate that is low enough not to upset the warranty claims department.

The point of it is in circuitry with flat responses from DC to the upper bandwidth limit, whatever that is, be it a scope or precision meter. In DC coupled circuits, with valves, drift is very problematic. So its easy to see why the test instrument makers quite rightly burnt in the valves.

But if it is for some audio amp application with AC coupled stages, it would be a WOMBAT to even consider pre-aging a valve (waste of money brains & time). Unless you believe in the supernatural audio forces.
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Old 3rd Dec 2019, 2:32 pm   #8
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Default Re: "Burning - in" Double Triodes

While not having strong evidence either way I must admit that on powering up NOS small valves particularly for the first time I have noticed a marked change of emission over time. My suspicion is that there is a burn in process maybe dispelling built up gas?

At the other end of the spectrum I did come across one article by a radio ham who had had issues with 6146 transmitting valves which failed soon after being put into use unless they were 'run in' first.

Perhaps there is little issue in most cases with small valves but, when pushed to the limit, it becomes a requirement?
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Old 3rd Dec 2019, 2:45 pm   #9
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Default Re: "Burning - in" Double Triodes

The thread that sparked all this off turned out to NOT be audiophoolery at all. The poster wants the valve for a Marconi Q meter and the marconi service manual instructs a repairer to run a new ECC82, whenever one has been fitted, in the DC amplifier for 100 hours before setting the balance and offset adjustments.

The circuit is using the ECC82 balanced to an extent substantially better than the side-to side match that the valves are made and tested to. I suppose it's to weed out any bottles which are a bit iffy for the application. This level of DC balance isn't something that would be needed for audio.

The original post didn't give any explanation, so I and others assumed the reason was the usual one. We were wrong.

My apologies to the original poster.

David
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Old 3rd Dec 2019, 2:48 pm   #10
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Default Re: "Burning - in" Double Triodes

I am not advocating burning in valves for use in general equipment, but in the specific context of a valve which is to be used as a standard for a valve tester, the results I've seen prove that it is essential.

The fact that a valve, indeed a valve which is some decades old, changes its characteristics to some degree during initial use is not too surprising.

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Old 3rd Dec 2019, 3:08 pm   #11
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Default Re: "Burning - in" Double Triodes

I have a Heathkit V-7A VTVM which I have refurbished. It uses one 6AL5 double-diode and one 12AU7 double-triode. Page 20 of the assembly instructions states:

" AGING. It is recommended that the tubes be aged before final calibration. This is accomplished by keeping the instrument turned on for a period of at least 48 hours."

I can see the sense in this, as the two halves of the double-triode may drift differently during this period and the maximum accuracy achievable is desirable. This might be referred-to as "burning-in", I suppose....

Colin (Not an audiophool).
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Old 3rd Dec 2019, 3:25 pm   #12
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Default Re: "Burning - in" Double Triodes

Valves are always 'burnt in' at te factory to activate the cathodes. It wouldn't be unreasonable to expect a valve not to have full emission the first hoursof use, especially if it has been stocked for long.
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Old 3rd Dec 2019, 5:16 pm   #13
David Simpson
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Default Re: "Burning - in" Double Triodes

A wealth of interesting replies. I seem to remember a similar thread a year or two ago - about "Soak Testing" O/P valves.
I can understand that some Lab grade T/Eq might well need the most stable of valves, and that "running them in" is a wise practice. I'm just a bit worried that the terms Burning & Soaking might be taken to the extreme by the audiophoolery brigade.
For most vintage radio/electronics pursuits - perhaps folk might switch on their test equipment for several hours a day, as a normal practice. However, I wouldn't recommend to the un-initiated to leave eq. running constantly for 100 hours flat-out. Just to comply with some questionable advice about NOS ECC valves.
Perhaps a wee safe B9A DC test rig could be built, by folk who regularly replace ECC valves in high-spec equipment. Otherwise, best leave well alone, & stay away from burning or soaking. In the VRR&R world, many of us use test eq. that is 40,50,60 or 70 years old. They " Wouldn't like it up em" - burning or soaking wise.

Regards, David
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Old 3rd Dec 2019, 6:34 pm   #14
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Default Re: "Burning - in" Double Triodes

In general, I agree that burning in is a form of audiofoolery, but as above not always.
Burning in serves at least two legitimate purposes, firstly to weed out any valves with latent defects before they are used in some critical application.
Not worth the effort for domestic equipment, but for specialist equipment in which an early failure might put human life at risk, or when later replacement is hugely costly, a few dozen hours burning in is prudent.

Also for test gear when the exact valve characteristics are crucial, so as to minimise drift in use. Better for any change in characteristics to occur during a few dozen hours of burning in, rather than during the first dozen uses of some specialist instrument.

For critical applications upon which human life may depend, even electric lamps were burnt in. Lamps for lighthouses were sometimes lit from a very well regulated supply for a few hours before being sent out.
The current drawn and the light output were accurately measured, and after the burn in, the bulb examined for any blackening.
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Old 3rd Dec 2019, 9:55 pm   #15
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Default Re: "Burning - in" Double Triodes

Burning in of new valves is mentioned in Langford-Smith's book. My experience is valves that have not been used for 70 odd years do change a little with use, probably due to gas absorption by the getter. Put an unused output valve on a tester and it may show grid leakage initially that decays if the valve is left on full power for maybe ten minutes.
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Old 4th Dec 2019, 7:34 am   #16
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Default Re: "Burning - in" Double Triodes

I'll throw another spanner in the works, I've heard this burning in, in reference to resistors too.

Andy.
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Old 4th Dec 2019, 7:45 am   #17
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Default Re: "Burning - in" Double Triodes

Quote:
Originally Posted by Diabolical Artificer View Post
......... in reference to resistors too.
And cables, and speakers, and just about everything!

The common factor is belief in something taken out of context without any substantiation.

Just a thought, those granite slabs and turntables and those little packets of 'brilliant pebbles'.... the stone parts are a few million years old. Cutting granite etc is a rather traumatic process (for the granite!) So shouldn't it be left for a while to bed in and 'burn-in? At least a few hundred thousand years before it is used for any critical listening?

David
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Old 4th Dec 2019, 10:24 am   #18
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Default Re: "Burning - in" Double Triodes

'Burning in' in general can actually work. We become used to the sound of our audio systems. If we change something for something else which sounds different then our first response can be to dislike the new thing, even if it's objectively better, simply because it's unfamiliar.

The best advice is "Stick with it for a while and get used to it". But some people are, as a British diplomat once said, 'advice-resistant', particularly if it's suggested that their hearing might be misleading them. So they're more likely to do what has to be done if they're told to "Stick with it for a while and let it burn in". The end result's the same but now everyone has ended up happier*.

Cheers,

GJ

*I accept that the customer's been left believing an untruth, and occasionally people have parted with their hard-earned in return for equipment which claims to 'burn in' their new item while they're away doing something else.
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Old 4th Dec 2019, 12:10 pm   #19
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Default Re: "Burning - in" Double Triodes

Quote:
Originally Posted by GrimJosef View Post
'Burning in' in general can actually work. We become used to the sound of our audio systems. If we change something for something else which sounds different then our first response can be to dislike the new thing, even if it's objectively better, simply because it's unfamiliar.
The thing is though, lets say a valve changes its properties in the first 100 hrs of use. What changes ? The transconductance can alter, the anode current can change for any specific grid voltage. What does that equate to ? A shift along the grid voltage vs anode current curve with a small change in the slope.

Absolutely nothing of any significance changes in an AC coupled amplifier. The shift in anode voltage is completely ignored by the AC coupling (and that is only for fixed bias , cathode bias largely eliminates the changes). The voltage gain changes a tad (so you adjust the vol control a few degrees) so what ? All you do if you burn in a valve for an audio amp application is shorten its total life.

However, in a circuit with DC coupled Paraphase amplifiers that require matched pairs of valves with stable characteristics, you have done a big favor for yourself if the valves are burnt in (and you weeded out any duds with early failure). So this makes sense and it is the kind of thing that was required before stable Silicon transistor based test instruments (signal generators, meters & scopes) were invented. This is why companies like Tek did it.

However if anyone in the audio field thinks its a good idea to burn in a valve used in an AC coupled audio amplifier, I think they need a reality check, or at a bare minimum, advice from an accountant who would explain they just wasted a 100hrs of life of the valve they just spent their hard earned money on.
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Old 4th Dec 2019, 12:34 pm   #20
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Default Re: "Burning - in" Double Triodes

Quote:
Originally Posted by Diabolical Artificer View Post
I'll throw another spanner in the works, I've heard this burning in, in reference to resistors too.

Andy.
Resistors don't have a cathode that changes in chemical composition, so that would indeed be the brain burning in as mentioned above, not the resistor.
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