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Old Yesterday, 08:59 PM   #1
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Default NL710, 6011

I just found a new in the box National Electronics NL710-6011 tube. I know from data sheets it is a gas and mercury filled thyratron tube but I have no experience with thyratrons. Could someone dumb down the function of a thyratron for me?

It seems it may make one very beefy rectifier but I may be wrong? If so could anyone provide a schematic of said tube used as a rectifier in a simple circuit? I am perplexed by the data sheet namely the "load return".
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Old Yesterday, 10:48 PM   #2
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Nice.
6011, Tube 6011; Röhre 6011 ID27818, Thyratron
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Old Yesterday, 11:20 PM   #3
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Thanks for the reply JonSnell. I am still in the dark though...
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Old Today, 12:29 AM   #4
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A thyratron is a rectifier with an added element that allows it to work as a switch. Because of the gas contained higher currents can be processed then vacuum alone. They are usually used for control of DC motors in machinery and phase angle control for AC rectification such as chargers and motor speed control. They cannot be used in audio for amplification and would be cumbersome to use as a standard rectifier. They're also electronically noisy to some extent. Different gasses are used to provide for a given service. Mercury vapor, xenon, neon and hydrogen are typical. Hydrogen is usually used for high kilo voltage environments like pulse forming networks and gas lasers. Many of the smaller and medium sizes have been replaced by solid state devices like silicone controlled rectifiers, thyristors and triacs.
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Old Today, 01:28 AM   #5
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A thyratron is the hollow-state equivalent of an SCR and behaves in a similar manner, though with a few extra quirks.
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Old Today, 12:46 PM   #6
Keit is online now Keit  Australia
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Like an SCR, it has a control element (the grid), which when made positive, ionises the gas and allows a large current to flow from cathode to anode. As the grid is closer to the cathode than the anode is, and is suitably shaped, the voltage required to start the internal arc is much much less than the voltage needed on the anode. Even if the grid voltage is removed, a thyratron will continue to pass current from cathode to anode, as long as the anode current remains sufficient to maintain the ionisation.

Typically the source of anode voltage is AC, so the device turns off at the next zero crossing, or the circuit provides for another thyratron or relay to force the anode voltage down so it turns off.

When AC needed to be generated from a DC source, two thyratrons were used, feeding a centre tapped transformer. A capacitor connected the two anodes together. The control circuit pulsed the grid of each thyratron alternately. When each thyratron turned on due to the grid pulse, it forced the other one off via the capacitor. So the transformer recieved a square wave.

As rectifiers, thyratrons are far more efficient than vacuum rectifiers, but are more expensive, and require too much control circuitry to be justified in domestic equipment. They don't last as long either. Anything that relies on internal arcing will slowly destroy its own electrodes.

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Old Today, 03:01 PM   #7
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Hmm--Mercury ARC Rectifiers.....

Last a LONG time! VERY long time! I know of one that is set into the wall of a cinema, not so far away from me and is behind a steel door like a safe in the rear wall of the projection-room, supplying the carbon-arc lamps and has been there since fitting--In 1920, by B.T.H....
Amazing thing to look at during operation, a large glass bulb over a foot and half tall with a liquid pool of mercury in the bottom, and glows a brilliant purple/blue colour

Usual voltage/current is 50-60A at 25-30V for a single lamphouse and on change-over the current doubled during the 2-5 or so minutes during the change-over....

(Two projectors used, each reel of film lasts approx 20 mins, full movie maybe say 10 reels for an 'epic' therefore change-overs used to show seamless full movie with two projectors)

Its now been de-comissioned a year or two ago with the so-called, 'Upgrade' to digital cinema, although was still working just fine at the time.
(Hmm--Upgrade, Digital Cinema --Aint!!)

Near a 100 years trouble-free operation--from a device that 'burns away' its electrodes aint a bad lifespan!.
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Old Today, 03:37 PM   #8
Keit is online now Keit  Australia
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Different thing.

Those big mercury arc rectifiers, often called Mekons (if you read the British comic "Eagle" in the 1950's, you'd know imediately why mercury arc rectifiers were called mekons) operated in a totally different way to things like thyratrons and gas tube voltage references. And they were made physically large so they would last awhile.

Still, even Mekons did have a limitted life and could fail unexpectedly. The high power (55 kW) radio stations I worked at one time kept a spare mekon on hand ready for changeover. A soon as high rating silicon rectifiers were invented, the mekons got the chop. Radio stations everywhere were happy to get rid of them. American high power broadcast stations built with more cash often had a changover mechanisn that could switch in standby mercury arc rectifiers automatically.

Ordinary reciving type vacuum tubes have a limitted life too. On average. But I have an old radio/PA I was given when an old factory closed 20 years ago. It was their music-while-you-work system. In operation 8 hours a day every day for ~ 50 years. The 6V6 output tubes (2 in push pull) have 1946 date codes. And still working perfectly. But will the bulk of 6V6's give 50 years life? No, nowhere near it.

There's a radio museum in my city that has a complete 1930's broadcast radio transmitter, big as a house, in operational condition, though of course there is no antenna and they don't have a licence to power it up. They even have the mekon. I feel scared just looking at it. As I recall it has at least a litre of mercury in it.

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Old Today, 04:15 PM   #9
Keit is online now Keit  Australia
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Quote:
Originally Posted by Alastair E View Post
(Two projectors used, each reel of film lasts approx 20 mins, full movie maybe say 10 reels for an 'epic' therefore change-overs used to show seamless full movie with two projectors)

Its now been de-comissioned a year or two ago with the so-called, 'Upgrade' to digital cinema, although was still working just fine at the time.
(Hmm--Upgrade, Digital Cinema --Aint!!)
The theatre must have had very stick-in-the mud managment.

There is a movie theatre not far from where I live. They re-furbished a couple of years ago, and invited us to have a look in the projection room.

I was surprised to find that they had two ways of showing movies. Projection of adverts, trailers, and main features was entirely digital, with content on DVD's (not standard retail DVD's) or acquired over the internet.

They have a policy of showing classics now and again, which are on 35 mm, not digital. These come in huge reels, one continous film per feature. Before showing, the projection staff re-spool them on huge horizontal platters about 1200 mm in diameter. The projector (there is only one per screen) has some kind of force cooled xenon lamp, there is no carbon arc system. It's been that way since the 1980's I gather.

There are multiple platters, but only one projector per theatre.

If the film is particularly popular, they run it simultaneously in two theatres. The film goes from the supply platter, through the projector, then to the second projector, with about 15 minutes worth of film going around various pulleys and passing overhead a few times in the projection room, and then to a take-up platter. So the second theatre runs 15 minutes behind the first.

It's all automated. The projectionist sets everything up at the start of the viewing day, perhaps three diferent features on digital, the ads (controlled by the ad company) and a couple on film, on their platters. He pushes the go button and then its all automatic. He could go home!

Last edited by Keit; Today at 04:23 PM.
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