Foregoing warranty rights

It's common knowledge in the electronics industry that if the "soiled" item is thoroughly flushed in/with distilled water, then allowed to dry (or forcibly dried), it will often recover. If the manufacturer advises the consumer to do this, and the device remains dead, the manufacturer could find itself liable for a free replacement. * In many cases, a customer could visit the nearest cell phone store and get a replacement in less time.

Nikon once ran an ad about a photographer in India who'd accidentally dunked his F. He carried it some distance in a bucket of fresh water (which was then standard for photo equipment -- you kept the camera wet until you got it to a service tech), periodically removing it to snap a shot! (It's not clear how the film survived this treatment.)

Almost 30 years ago, while on a canoe trip, my Olympus XA got completely immersed. I immediately bought another one, but I discovered -- several years later -- that it still worked! And it still is working! It didn't rust or corrode. Amazing. Structural plastics -- ya gotta love 'em.

• About 15 years ago, I took my HP 4M into work, because we were doing so much printing there weren't enough printers to go around. (The company later bought me a replacement toner cartridge.) As I was carrying it out of my apartment, the paper tray came loose and crashed on the concrete steps, breaking. This was around the time of a major California earthquake, and HP had run an ad telling how another model of laser printer had fallen to the floor without damage. I pointed out that HP couldn't very well use this fact as an inducement to buy their products, then object when I asked for a replacement tray that had been subjected to similar abuse. After some haggling, I was sent a slightly used tray at no charge.

Actually, modern microwaves are more tolerant. You can put a metal tray in a microwave, and nothing bad will happen.

The issue isn't metal, per se -- a metal plate reflects microwaves as the cavity walls do -- but sharp spots at which the field intensity is so high that you get corona discharge or arcing.

I once put a jar of Adam's peanut butter in the microwave to warm it -- and you should have seen the arcing at the tiny -- really tiny -- bits of aluminum that were left on the lip from the seal.

Yep. Some come with metal racks:

As long as there is something inside the oven cavity that will ABSORB the RF power, it's safe. Take away the absorber, such as with an empty microwave oven, and the resultant standing waves will build up a sufficiently large field to initiate arcing.

Of course, put anything, except food, in a microwave oven, and your warranty is torched.

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Jeff Liebermann     jeffl@cruzio.com
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Even with something to absorb the energy, you can still get arcing from sharp metal edges.

You'd certainly get arcing from the pins. It's not obvious (to me) how the tube's elements would react.

On 4/3/2011 5:29 AM Geoffrey S. Mendelson spake thus:

So--and this is completely out of left field, I know--what would happen if a guy put a vacuum tube--say a biggish octal one, like a 5Y3 or a

6V6--into a microwave and nuked it?

I've nuked CDs and derived many seconds of amusement from that ...

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Unfortunately, there's no gas in a "vacuum" tube to glow.

On 4/3/2011 3:42 PM William Sommerwerck spake thus:

Ah, I forgot about the pins. OK, let's say we really have too much time on our hands and want to continue the experiment, so we get something to plug the tube into, say a pin straightener, with no exposed metal. What then?

(What I'm hoping for, of course, is some kewl effect, like that purplish glow you sometimes see emanating from the plates of overdriven tubes ...)

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"David Nebenzahl"

** The blue/ purple glow is emanating from " impurities" in the glass - it is generated by electrons hitting the glass at high speed.

Most audio power tubes (ie 6L6GCs, EL34s, EL84s and 6550s ) have cut outs in the plate structures that allow this to happen.

The blue glow will be there when the tube is new ( if it's there at all ) and is not a sign of a problem.

It may be fairly steady or respond to high drive levels - ie when the plate voltage nearly doubles in magnitude with signal peaks.

.... Phil

Impurities in the glass envelope or gas in the tube.

If gas, take an anti-acid tablet and you should be fine in a few minutes.

Scroll down to: C. Blue Glow -- what causes it? for more details.

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Jeff Liebermann     jeffl@cruzio.com
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On 4/3/2011 5:05 PM William Sommerwerck spake thus:

So where does that purplish glow come from? I've seen it.

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So even after a getter flash there is still a certain amount of impurities? I've never seen a 6L6 that didn't have some blue inside when in operation. It looks as though the blue only occurs where the electron beams hit the inside of the glass. At least in new tubes.

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You mean, 'nuked it AGAIN', don't you? The usual manufacturing of vacuum tubes is finished off with pumpdown, sealing, and then running an induction coil to heat the little loop-thing that evaporates a bit of metal (like sodium). It's called 'flashing', and the silvery deposit ('getter') on the inside of the tube is intended to be an oxygen scavenger for the long lifetime of the device.

In the case of photomultipliers, it is also done to create the photocathode layer, often of some alloy that cannot be usefully blended until there's a vacuum.

They use getters in metallurgy to absorb impurities. The getter is actually the "little loop-thing" and not the deposit that is a byproduct of the flashing. Some getters are made of a special material and don't need flashing. Don't ask me for a tube number. Tubes with graphite plates don't need a getter as the graphite absorbs impurities.

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Yep. As I vaguely recall (which means I didn't Google for a reference) glass has the irritating habit of collecting impurities and volatiles during manufacture. Irving Langmuir figured this out in the

1920's working on light bulbs. He would draw the best vacuum possible and in a few days, find the bulb full of water vapor and other gasses. The hot filament would break down the water into hydrogen and oxygen. The oxygen would then oxidize the electrodes, and blacken the inside of the bulb.

So, he invented a method of baking the glass to remove the volatiles prior to evacuation and an acid bath to remove some of the impurities. It also works nicely for vacuum tubes, but like all such processes, is far from perfect. There's always some impurities left behind.

When we talk about a "gassy" vacuum tube, it's not a leaky glass envelope or seal. The getter does best with reactive gases and does nothing for eliminating noble gases, which will not react with metals (or most anything else). It's those noble gases that remain (helium, neon, argon, krypton, xenon, and radon) that you're seeing glow. Most likely helium and argon mix. The small helium molecule will also diffuse through the glass from the outside air. See photos at:

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"Jeff Liebermann"

** The term covers that eventuality too.

Any tube that has even a tiny air leak will glow a pinkish purple inside like a bastard.

** Maybe - but how would any significant amount of Argon get inside the tube UNLESS there was air leaking in ?

Remember, Argon makes up less than 1% of air and does not react with metal parts.

The vacuum inside a tube is less than one millionth of atmospheric pressure.

BTW:

Nitrogen mixed with a little CO2 makes a nice, white glow under low pressure - its called a "Moore Tube"

His untimely death was a bit shocking.

.... Phil

Ok. My bad grammar. I meant that if the tube is deemed "gassy", it's probably not an air leak in the envelope or seal. It's more likely gaseous diffusion of helium or neon through the envelope.

Yep. I've seen the pink glow. The only way I could tell the difference between the nitrogen glow of an air leak:

and that of a helium diffusion through the glass leak:

was that the nitrogen glow would not last very long as the filament would burn out due to oxidation.

Oops. Y'er correct. Only helium and neon will diffuse through glass. Argon and larger gas molecules won't diffuse through glass.

Yeah, but the pressure differential is 14.7 lbs/sq-in. Over the surface of the 6L6, that's about (assuming a cylinder): Surface Area = 2 Pi r^2 + 2 pi r h = (2 * 3.14 * 0.7^2) + (2 * 3.14 * 0.7 * 3.0) = 16 sq-in Surface pressure = 16 * 14.7 lbs/sq-in = 235 lbs. (Yes, I'm guessing at the dimension for a 6L6 as I don't have one handy). That's quite a bit of pressure pushing the helium and neon atoms through the glass. Still, for helium, the diffusion rate is slow (helium through pyrex at STP):

8.0 x 10^-8 m^3/hr

I guess his murderer didn't do a proper patent search before starting work on his invention. We're more civilized these daze. Instead of murder, we have litigation. It's much like murder in slow motion.

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Jeff Liebermann     jeffl@cruzio.com
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"Jeff Liebermann" "Phil Allison"

** Unfortunately, that idea is at odds with observations of tubes that show internal glowing.

Egs: It happens to tubes that are used or not and are old or not PLUS most even very old tubes show no sign of gas.

The only correlations I have seen are:

1. Certain batches all have the issue.
2. Tubes that have suffered long term overheating.
3. Tubes with visible corrosion on the pins and / or cracks in the glass near the pins.

..... Phil

This is way OT, but Chicago Miniature Lamp claimed that helium diffusion shortened the life of incandescent lamps.