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Old 4th Apr 2015, 10:10 am   #1
bobmeades
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Default Valve Manufacture film

https://www.youtube.com/watch?v=dErsA6wFmlM

Sorry if this has been posted before - but as someone who has swapped & changed a few valves over the years, I have often wondered how these delicate gizmos could ever be made in quantity - well this fascinating video from Mullard shows how.
Bob
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Old 6th May 2015, 5:41 pm   #2
Colin Ames
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Default Re: Valve Manufacture film

Very interesting. Thanks for posting the link.

Colin
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Old 9th May 2015, 7:14 pm   #3
SurreyNick
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Default Re: Valve Manufacture film

That really is a most informative film Bob. It makes one appreciate why valves were relatively expensive items.

I would love to know what the defect rate was. A lot higher than today's standards I expect. Motorola set a goal of "six sigma" for all of its manufacturing operations, which is a defect rate of just 0.00034%! Seeing the number of valves being rejected at one stage of the process in the film I doubt they even got to sigma 3 (6.7% defective). For the complexity and fragility of the manufacturing process and given the technological limitations of the time I reckon even sigma 3 would be one heck of an achievement.

Nick.
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Old 9th May 2015, 9:33 pm   #4
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Default Re: Valve Manufacture film

The 'Six Sigma' business is more understandable if it's viewed the other way around:

The pass/fail limits of parameters come first. They are set by what works and doesn't work in the target application. The manufacturer then has to get his processes sufficiently well controlled that the standard deviation (sigma) of the scatter of the parameters is less than one sixth of the fail limit. This is a remarkable achievement.

The theory then says that if the distribution is Gaussian, then 0.00034% will be failures.

Measuring the standard deviation of the process is not difficult, but measuring such low failure rates is going to take a very long time to get a trustworthy result.

There is a flaw in the theory, of course. There is now a whole 'Six Sigma' industry with firms selling training and consultancy. What few of them teach is that the foundations are a little bit shaky. The assumption that distributions are Gaussion comes out of the central limit theorem which says that if the scatter of a parameter is the sum of a great many small contributions AND that those contributions are independent of each other then it doesn't matter what the shape of the distribution of each contribution is, the way they add will make the overall parameter tend to a Gaussian shape.

Taking the ideal Gaussian shape, one can measure the width of the bell near the centre where there is a large population, and from this, one can extrapolate the probabilities of values happening much further out, where events become very infrequent.

The problem is that if there are any small systematic linkages due to the process, they may make only relatively tiny errors in the Gaussian bell shape near the centre, but they can make relatively massive differences in failure rates out where the curve is very close to zero.

Getting a process so that sigma is a sixth of the acceptance limit is still a great achievement. But don't rely solely on the extrapolation, keep an eye on the long-term smoothed failure rate. It can sometimes have a surprise factor of an order of magnitude or two.

I worked in the precision measuring instrument business and we employed a professional statistician to monitor things and train people in statistical process control and design of experiments. the concepts were subtle, but the results translated into quite spendable money.

The Mullard film shows hand assembly for the purpose of illustrating what is in a valve. It doesn't show the machine-based processes which are needed to get extreme conformity. good machines, good jigs and skilled human supervision of the machines is needed for closely controlled parameters.

Here we are, many years later and far, far, out on the bathtub curve. We know from experience that the repeatability and life expectancy of the valves made at Blackburn was excellent. If we ignore the auto-suggestive stuff about pace and rhythm and the colour of the labelling, the reliability is absolutely real and proven.

I'm afraid that several manufacturing industries have shown that mechanisation and huge turnover are the routes to tightly controlled parameters and reliability. The highly expensive cars with a lot of hand assembly are the most unreliable which money can buy. I don't think there was really a matching luxury/ mass market in radio or TV because the posh sets were really the same chassis fitted in a fancy cabinet.

Mullard was part of Philips, and evolved into a semiconductor manufacturer, and then got renamed and floated off as "NXP". They must still be doing something right, because they've just bought Freescale which was formerly the high performance semiconductor side of Motorola.

I'm glad they made those films. It would be a shame if such a wonderful achievement was forgotten.

When the Beatles sang of 'Four thousand holes in Blackburn, Lancashire" I thought they were underestimating (poetic licence) the number of holes in a shadowmask.

David
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Old 10th May 2015, 12:37 am   #5
AC/HL
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Default Re: Valve Manufacture film

If you type "Mullard film" into the search box above, you will find more similar threads including this one: https://www.vintage-radio.net/forum/...d.php?t=106283
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