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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 4th Dec 2019, 12:48 pm   #21
Radio Wrangler
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Default Re: "Burning - in" Double Triodes

In the high end audio world, there are several principles which are not allowed to be challenged:

There is no limit to the discrimination of the hearing of a true audiophile.
No factor is so small that it can be dismissed from consideration.

Valves degrade progressively with time, emission falls, Gm falls, gas enters. The degradation over the first 100 hours is going to be very small indeed (for valves without manufacturing flaws) but audiophiles aren't allowed to think it doesn't matter.

So they haven't just dumped 100 Hours of their valve's life expectancy, they've dumped THE BEST 100 hours of its life

Unless they were there listening through the whole of the burn-in period, the best hours were wasted ....Using their own logic for a bit of fun.

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Old 4th Dec 2019, 1:55 pm   #22
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Default Re: "Burning - in" Double Triodes

'Burning In'

* To remove the mortal infants (weed out the early failures badly made).

* To stabilise characteristics. I have seen Mullard data which gives design ratings for characteristics for maximum cathode current, with a footnote that for a new valve a higher rating might apply. (TV timebase output valves). So a designer making a trial circuit would use a valve well 'burned-in' not a new one from Stores.

* Other components - electrolytic capacitors are well-known to deteriorate in storage. A period of time to re-form can be necessary before full performance is regained. We wouldn't call it burn-in, but as it is the same process of putting power on and waiting, then yes it can and does make a difference!
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Old 4th Dec 2019, 2:52 pm   #23
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Default Re: "Burning - in" Double Triodes

Regarding 'audiophoolery' - the burning in or running in process certainly does have an affect with speakers.
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Old 4th Dec 2019, 3:17 pm   #24
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Default Re: "Burning - in" Double Triodes

Quote:
Originally Posted by RF Burn View Post
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?
To me it certainly is general knowledge, but that can also be because I know that freshly mounted (picture tube) cathodes even need to go through an activation procedure including some "overvolting" to work properly at all. It makes very much sense that the first tens of hours of normal use will still see some change, especially after having been stocked for some time.

Anything with chemical or mechanical action as its main working principle that has been stocked will exhibit some changes in characteristics when first used.
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Old 4th Dec 2019, 7:00 pm   #25
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Default Re: "Burning - in" Double Triodes

I have heard of burnt out resistors, back on topic (ish), if you twiddle a tone control of (say a mates) HiFi a bit by another bit over an hour or so I bet they won't notice until it has gone 20 degrees or so!
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Old 4th Dec 2019, 8:53 pm   #26
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Default Re: "Burning - in" Double Triodes

It's all very well this talk about how valves change from the day are they made through the period in which they are used/listened to. I, and thousands of others get that, we know that! The point is, can it be HEARD?!

Like David (aka Radio Wrangler) says:

In the high end audio world, there are several principles which are not allowed to be challenged:

There is no limit to the discrimination of the hearing of a true audiophile.
No factor is so small that it can be dismissed from consideration.

Quite simply, we're participating in another audiophoolery thread. ABX testing, that'll provide REAL answers!
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Old 4th Dec 2019, 9:12 pm   #27
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Default Re: "Burning - in" Double Triodes

Quote:
Originally Posted by stevehertz View Post
It's all very well this talk about how valves change from the day are they made through the period in which they are used/listened to. I, and thousands of others get that, we know that! The point is, can it be HEARD?!
Indeed.

I would say that a well-designed amplifier should be able to tolerate - without significant malfunction - small variations in the characteristics of valves during their lifetime.
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Old 4th Dec 2019, 9:25 pm   #28
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Default Re: "Burning - in" Double Triodes

Amplifiers, yes. Electronics in general - harder question.

I do recall Smithy explaining to Dick that failure of a TV frame-hold or line-hold to be adjustable to the correct frequency could be just due to the unlucky insertion of a valve with a grid cut-off voltage a bit more extreme than general. He explained that cut-off is subject to fairly wide variations between samples, and in a multivibrator it does affect frequency.
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Old 4th Dec 2019, 9:27 pm   #29
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Default Re: "Burning - in" Double Triodes

Quote:
I would say that a well-designed amplifier should be able to tolerate - without significant malfunction - small variations in the characteristics of valves during their lifetime.
I would go further, it should cope with at least +/- 30% changes in characteristics without any real change in measured specs. and not malfunction at all. Semiconductor amps. cope with huge variations (as made!) in transistor characteristics.
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Old 4th Dec 2019, 9:29 pm   #30
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Default Re: "Burning - in" Double Triodes

when I was in the telly game doing repairs at the bench all TV's that had new valves fitted as part of the servicing were soak tested for at least a day or two, quite often after that period the picture height and the picture width would need a re-tweek, so yes a kind of burn in so to speak, same for new mains droppers, anyone in the TV trade back then will tell you how new ones used to stink, send that back to a customer and you'd get a bouncer call, so again a soak job on the soak bench, burning in the dropper resistors if you like....So "burning in" as a term isn't really total bunkum, not to me at any rate....

Lawrence.

Last edited by ms660; 4th Dec 2019 at 9:35 pm. Reason: spelling addition
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Old 5th Dec 2019, 12:19 am   #31
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Default Re: "Burning - in" Double Triodes

Quote:
Originally Posted by stevehertz View Post
It's all very well this talk about how valves change from the day are they made through the period in which they are used/listened to. I, and thousands of others get that, we know that! The point is, can it be HEARD?!
This would probably depend on the circuit. I think the most important change in tube parameters is in the emission, so I think the mutual conductance would be affected as well. In a good design this is compensated with a feedback loop, but especially audiophile designs might depend a bit more on the open loop performance.

Also possibly the bias could be affected. Again, depending on the circuit. A low idle current may result in more distorsion.

P.S. I don't think we're participating in an audiophoolery thread since the thread title is more general; even if the difference can't be heard in a good audio design, it can be seen in television sets and measuring equipment. And probably heard in bad designs.
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Old 5th Dec 2019, 10:52 am   #32
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Default Re: "Burning - in" Double Triodes

Quote:
Originally Posted by Maarten View Post
Quote:
Originally Posted by stevehertz View Post
It's all very well this talk about how valves change from the day are they made through the period in which they are used/listened to. I, and thousands of others get that, we know that! The point is, can it be HEARD?!
This would probably depend on the circuit. I think the most important change in tube parameters is in the emission, so I think the mutual conductance would be affected as well. In a good design this is compensated with a feedback loop, but especially audiophile designs might depend a bit more on the open loop performance.

Also possibly the bias could be affected. Again, depending on the circuit. A low idle current may result in more distorsion.

P.S. I don't think we're participating in an audiophoolery thread since the thread title is more general; even if the difference can't be heard in a good audio design, it can be seen in television sets and measuring equipment. And probably heard in bad designs.
I suppose I erroneously broadened the scope by talking about how valves change from the day are they made through the period in which they are used/listened to. The original issue was, do they need to be burned in? That being the case, then the subject of emission will not (should not!) be an issue in during an upfront period termed as burn in.
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Old 5th Dec 2019, 1:51 pm   #33
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Default Re: "Burning - in" Double Triodes

So the question here seems to be;

“During the initial period of use, do valves change their characteristics such that either;

i) the change is measurable using a either a simple DC test set or a VCM
ii) The change has a demonstrable effect on the performance of the equipment the valve is being used in”.

And the follow-on question is whether data exists that proves anything one way or the other?

I’ve spent quite a lot of time measuring the DC characteristics of valves in pursuit of having a good reference or “standard” valve(s) for use to check readings from my VCM163. The first valves I used for this were ECL80’s, then EF91’s and then I finally settled on ECC81’s (the reasons for this progression are significant but off-topic). In each case, I’d laboriously characterise the valve by hand on a DC test setup, paying due regard to accuracy and reproducibility (during the course of which, I verified Tanuki’s assertion that every amplifier wants to be an oscillator). What I will say is that the data I gained convinces me that that burn in does occur.

As David Simpson (OP) will recall when he initiated a comparison of valve tester measurements on this forum, the readings I got from my 163 on a valve which he had standardised were extremely close, so my “doings” have some kind of validation wrt the outside world.

But by way of other data, the attached PDF shows a plot of change in emission, taken from a paper called “Electron Emission for the Oxide Cathode” by C.H.Meltzer and E.G.Widell. This is from either an American book or conference proceedings in the early 1950’s, but the full reference was not supplied to me. I didn’t fake it and I’m sure that numerous other papers can be found showing the same thing – this was just the first paper I found in my files.

As for whether or not burn-in affects the performance of equipment, I have only my own thoughts on that and no data whatsoever on that, so I stay silent on the matter!

I'm sure that others have more data?

B
Attached Files
File Type: pdf emission w.pdf (281.9 KB, 32 views)
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Old 5th Dec 2019, 5:27 pm   #34
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Default Re: "Burning - in" Double Triodes

Right enough, Bazz, like myself, likes to keenly delve into the pure DC characteristics of many valves. His 163, like my DC tester, came jolly close to Martin's super duper RoeTest . Trouble is, we, like most folk in the vintage radio fraternity, power our test eq. with domestic mains. Also, much of Forum folk's T/Eq. is 2nd hand, and maybe clocking-on in years. Hence it would be difficult to determine the extent of any burning-in efforts.
Such advanced accuracy might be attained at the NPL, or at Agilent's HQ, etc. But, I doubt that in these digital electronics 21 century days that any professional electronics experts give a toss about analogue valve technology.
As I said earlier, it was '66 when I first became involved with RAF T/Eq. repair. I don't remember being told at the time, but maybe the replacement new CV valves we used had been initially been "burnt-in" by Mullard or whoever. Or were burnt-in at RAF Henlow which was the premier T/Eq. MU. There is a perception that CV valves are of a better quality anyway than shop-bought civilian ones. Who knows.
I just worry that "burning-in" becomes an audiophoolery fad, or a ploy by internet valve mercenary wheeler-dealers to enhance their sales pitch.

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Old 5th Dec 2019, 7:04 pm   #35
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Default Re: "Burning - in" Double Triodes

The only valves (if I can call them that) which needed burn in were when replacing the Magnetron in the ships radar transmitter. You had to run the Magnetron on heaters only for a good length of time, then bring up the HT slowly from zero to 28kV in step changes. It was called hardening of the Magnetron, fitting one straight from stores and running at full power would result in its early demise.
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Old 5th Dec 2019, 7:48 pm   #36
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Default Re: "Burning - in" Double Triodes

True. And mercury vapour rectifiers need to be burned-in with heater only for half an hour after installation or any movement of the bottle involving inverting it, before applying power.
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