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Old 19th Aug 2018, 10:07 am   #1
Russbrown
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Default Mercury Arc Rectifier. Value?

I recently came across a mercury arc rectifier in a friend's warehouse and he was looking to sell it. It is unused and in the original packaging crate which stands about 6 feet tall. Seen in photo attached.

Please could anyone give me some advice on who might buy it and what it is worth?

Thanks.
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Old 19th Aug 2018, 11:05 am   #2
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Default Re: Mercury Arc Rectifier. Value?

It's quite a large one. They aren't used significantly nowadays, so it's unlikely anyone would buy it for its original purpose. They were used to convert mains power into DC, there was one in a stone building powering the trolley busses to our village. Some were used for large DC motors in factories and even revolving stages in theatres.

So a purchaser would likely want it for display. It would take a fair amount of gear to light it up properly, and the running costs would be significant. They don't look a tenth as interesting unlit.

There aren't many around, so rarity acts to increase the price. There aren't many people who'd have the space and power to display it running, so that acts to decrease the price.

On top of it all, it contains a serious amount of mercury and if it got broken/spilt it would now be treated as a very serious incident needing expensive decontamination. So the fear of liability gets in on the pricing. So the rarity of possible buyers matches the rarity of the things - meaning the price could go anywhere, depending who turned up at an auction. I don't see any on ebay, just a small mercury diode. Maybe the amount of mercury excludes them under their rules?

There have been people on here looking for them. A couple of regular denizens have MARs set up for display. But this forum has a strict rule that items in the for sale section must have a stated price. The site's operators had some experiences stemming from discussions of items on auction sites which they (quite reasonably) have no wish to risk repeating.

It may be of interest to a mainstream bricks and mortar auction house that occasionally has auctions of technical equipment. This might give the best outcome

I remember as a kid pushing the button on the demo one at the science museum. Just a small one in a wooden cabinet with a UV-proof viewing window. The one in our village produced a glow through the louvres of the building's doors.

There should be a maker's name and type number somewhere.

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Old 19th Aug 2018, 11:11 am   #3
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Default Re: Mercury Arc Rectifier. Value?

A considerable sum to someone who wants it. Totally irreplaceable and worthy of preservation.

Selling it is fraught with problems due to the current status of mercury as a controlled dangerous substance.
Just moving it requires special notification and precautions.
Selling it on the open market may be illegal.
I tried to export some valves, customs destroyed them quoting the law about transhipping "mercury" which they were devoid of anyway. All just because they were shiny silver.
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Old 19th Aug 2018, 11:48 am   #4
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Default Re: Mercury Arc Rectifier. Value?

I would suggest you contact Lucien Nunes, either by private message on this forum (https://www.vintage-radio.net/forum/member.php?u=7602) or through his Electrokinetica website http://www.electrokinetica.org/d7/1/index.php.

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Old 19th Aug 2018, 3:11 pm   #5
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Default Re: Mercury Arc Rectifier. Value?

Hi

There is a good chance it's a used one, it would have been normal to put the old one in the crate a replacement came in, for safe transportation.

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Old 19th Aug 2018, 3:22 pm   #6
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Default Re: Mercury Arc Rectifier. Value?

Whether it's used or not might be determined by the burn marks. New ones will have been tested prior to shipping so there will always be marks.

Lucien's advice will be good.

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Old 20th Aug 2018, 10:37 am   #7
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Default Re: Mercury Arc Rectifier. Value?

It does indeed look as though it has been used, as a new bulb is usually pretty much completely clear. Whether that means it is faulty is another question. As mentioned above, faulty bulbs were returned to the manufacturer for repair using the supplied crate, but after they closed or stopped accepting repairs, used bulbs both good and bad were sometimes parked in the crates that had once held on-site spares.

The snag is that it is quite hard to test whether or not a bulb is intact, unless it can be test-run in the equipment it belongs to. They were inherently reliable but as they age, the seals can become more fragile and as soon as one fails, air starts to enter the bulb rendering it useless. At the moment I am not aware of anyone who has proven resources for refurbishing them; the small number in preservation makes it an unlikely venture. Historically, there was a rather frightening procedure for testing the vacuum, that involved tilting the bulb so that mercury surged down an exciter arm and listening to the sound it made when it hit the end. The sharpness of the click depends on the gas pressure - even a small amount of air cushions the mercury and dulls the sound - but the nice sharp click of a new bulb is also the most likely to result in the mercury busting out through the end of the arm, or at least damaging the very seal that was being tested. The result of this is that even unused bulbs will always be a gamble until they are connected up. I am part-way through making a portable tester but the project is on a back burner.

Simple checks you can make include very gently pulling / pushing the metal terminal caps (DO NOT TWIST!) to check for looseness. Look at what would be the top side of the arms when right-way-up and check for pinholes or sagging above the graphite anodes that would indicate overheating. Shine a torch at the surface of the mercury to check for glass fragments or droplets of condensed water. The reason I am recommending studying it closely is that if the bulb is no good, the cost of disposal is significant, as mercury no longer has much of a value to offset the decontamination cost of the remainder. Sadly a lot of bulbs, even new good ones, have been broken up and removed by hazardous waste contractors, who charge for the service. This is reflected in the likely value of a used, untested bulb.

Assuming your bulb is actually OK, it's rather nice. ECC were one of the four main UK makers, and their seals have stood the test of time well and rarely fail without provocation.The serial number under the logo may be the only identifying information, but I don't know of any way to reference it. It looks to be something in the region of 250-300A and very much like the bulb in my avatar which is a 350A ECC. If it were 350A, it might suit one of our units that takes four bulbs, two of which turned out to be damaged, but the arms look the wrong shape for that current. Depending on your location I might be able to take a look.
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Old 20th Aug 2018, 12:31 pm   #8
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Default Re: Mercury Arc Rectifier. Value?

Well that sums it up quite well.

One thing is for sure- any (serious) buyer of a mercury vacuum tube of this size will be resigned to the fact that he will have to collect it him/herself.

Value is highly speculative and fluid due to all the reasons already mentioned, the pictured item is inverted, and MUST be kept in this orientation in transit. Having the crate and straps is an advantage, but it would still be an idea to load the free space in the crate with expanded plastic packing material before moving it any distance.

Dave
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Old 20th Aug 2018, 12:44 pm   #9
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Default Re: Mercury Arc Rectifier. Value?

Super post from Lucien!

I'd heard of the tilt technique as a way of seeing if the thing has gone to air. Sounds very risky!

The only thing I'd add is that, while upside-down for transit, even turning right-way up for service is a non-trivial task. As someone who has difficulty carrying a flat tray of water, the idea of righting a bulb of heavy mercury, without it sloshing into an arm and knocking it off (without a buffer layer of air!) would fill me with trepidation.

Super thing to put in service and use, though...
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Old 20th Aug 2018, 12:48 pm   #10
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Default Re: Mercury Arc Rectifier. Value?

In a previous life I had occasion to deal with some of these. I also had to deal with the disposal of mercury and other hazardous chemicals. All of it ended up at Ellesmere Port where it was dropped, still sealed in clip top drums into the incinerator at 1200 C. I'm not sure if mercury was separated and anything special happened to it as once the specialist contractor had driven away with it, it was out of my hands.

I actually had a small one at home for years as an ornament, but in the end, and rather reluctantly, I decided that it was just too much of a liability for my relatives to have to deal with if and when anything should happen to me, so one day I took it into work and it went with all the rest. This was now many years ago and it was even wrong to transport a thing like this in a car on the public road. In fact, on our site there was a public road that ran right through the middle of the site and if any chemicals had to be transported to a building on the other side of the road, then a specialist contractor had to be brought in to do it in a vehicle with special containers. Because of this it was cheaper to duplicate certain chemicals in the different sections to avoid this, or some might take the risk and just take the substance across the road and hope nothing happened.

So no, you can't transport one in a family car. If you were involved in an accident your insurance would be void and the cleanup of the spill would be serious and expensive, and you'd certainly be prosecuted. You can't post a thing like that, although I'm guessing that it's been done. The trouble is that irresponsible posting (with probable bad and ineffective packaging) is one day going to cause a serious incident, with risk to postal workers health and life. It's already getting difficult enough to be allowed to post certain items due to what they contain and it's only going to take a serious incident in a sorting office or some such place (that doesn't bear thinking about with mercury all over the place) caused by some irresponsible person for there to be a total clamp down altogether that will affect all of us.

I've personally had to deal with quite a number of in some cases fairly serious mercury spills, and I can tell you that it's not funny!
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Old 24th Aug 2018, 10:11 am   #11
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Default Re: Mercury Arc Rectifier. Value?

The mercury is probably the most valuable bit of that! Crack off one of the nipples, bottle up the mercury and flog it.
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Old 24th Aug 2018, 10:54 am   #12
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Default Re: Mercury Arc Rectifier. Value?

Many good bulbs have been broken for their mercury in the past when it had a higher value than it does now. Improved recycling and lower industrial demand have depressed the value of recovered mercury to the point where it may cost more to transport than its market value. If the bulb is faulty, then yes, selling the mercury may offset the cost of disposing of the envelope. But we don't know that yet; it might be perfectly good. Now they are hard to find, for those who want them, intact bulbs are worth preserving, especially when they are in an available situation.

There are still bulbs present on industrial sites that will never be available to collectors, because of the complicated paper-trail involved. Even where the site wants to dispose of the bulb and someone else wants to acquire it, there are sometimes administrative obstacles that result in the site having to pay a licenced waste contractor to destroy it. This is almost as frustrating as seeing good radiograms etc being scrapped to liberate their valves / chassis for sale to a different market sphere, but with mercury-containing items it is more an unwanted side-effect of hazardous waste legislation than deliberate vandalism.
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Old 24th Aug 2018, 11:35 am   #13
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Default Re: Mercury Arc Rectifier. Value?

Seeing that rectifier triggered a memory. When I visited the Kempton Steam Engine I remember seeing a couple running, perhaps they may be able to help regarding what to do next?
The link for the museum is here: http://www.kemptonsteam.org/
There is a picture on there which, if you look at the bottom left hand corner, you may just be able to make out their outline, double clicking on the picture enlarges it.
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Old 24th Aug 2018, 11:51 am   #14
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Default Re: Mercury Arc Rectifier. Value?

Presumably you mean here:-

http://www.kemptonsteam.org/history/arc-rectifiers/
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Old 24th Aug 2018, 12:46 pm   #15
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Default Re: Mercury Arc Rectifier. Value?

Quote:
Originally Posted by daviddeakin View Post
The mercury is probably the most valuable bit of that! Crack off one of the nipples, bottle up the mercury and flog it.
It's not worth anything. It's totally valueless and just a liability.

Back in the day it had considerable value. I remember the time when at work back in the 'old days' we used to smash them up and bottle up the mercury. Then, when enough had been saved, someone would take it down to one of the local scrap merchants that also had a tool shop that fronted the street. They would weigh it round in the yard at the rear and issue a 'chit' to the value which was used in the shop part of the business to buy tools for the workshop. This was before the safety aspects of mercury were fully understood. I never personally broke any or took any mercury to the scrap merchant, but one of my work colleagues made it his 'passion' and many new tools were obtained in this way. It was years later when I became involved in having to dispose of many kilograms of horded mercury that had no value and had become a dangerous liability.

Now it's worth absolutely nothing and costs money to have it taken away. There is an over stock of mercury in the world now, and it has little or no use in industry or anywhere else.

I still have moments of regret about disposing of my rectifier, but sense had to prevail. It really is a great shame that there's become this problem with regards to saving these rectifiers due to the mercury, but having dealt with bad spills in the past and the fact that once it gets out it really does get everywhere and is a complete nightmare to deal with, it's best to just not have it around in the first place.
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Old 24th Aug 2018, 1:56 pm   #16
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Default Re: Mercury Arc Rectifier. Value?

Quote:
Originally Posted by Techman View Post
It's not worth anything. It's totally valueless and just a liability.
If anyone has any mercury, I'll take it off your hands!
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Old 24th Aug 2018, 4:48 pm   #17
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Default Re: Mercury Arc Rectifier. Value?

Mercury, what a surprise.!! I went skip digging the other day and came across a step-counting exercise torture device. I decided to pull the electronics out of it for curiosity. Inside was a small chip on board PCB with a glass vial mercury filled "tip" switch, in content there is a 3mm diameter ball of mercury as the make "contact" for the switch.
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Old 24th Aug 2018, 10:53 pm   #18
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Default Re: Mercury Arc Rectifier. Value?

I've also heard that Mercury Arc Rectifiers give off quite a lot of UV light when in use which can be another health hazard.

They were once common on the London Underground for converting power for lift motors & other equipment. One of the closed stations occasionally opened for special visits has some still installed. I think it's one that was turned into a bunker in the 2nd World War.
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Old 24th Aug 2018, 11:47 pm   #19
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Default Re: Mercury Arc Rectifier. Value?

Can't quite remember but ISTR either Crich Tram Museum or the Black Country Museum using one for their tram or trolleybus, I forget.
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Old 25th Aug 2018, 12:02 am   #20
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Default Re: Mercury Arc Rectifier. Value?

Sorry, but messing around with mercury is like messing around with radium paint or blue asbestos- it's dumb, just don't do it! OK, in the past folk had to work with all three to put food on the table, but we've moved on and the hazards are known and available to all in the public domain. Other than the man-made plutonium, it's the most poisonous and insidious element there is, a lingering and dangerous substance even in tiny quantities that it's unfair to risk exposing others to just because "I don't mind the risk".

https://en.wikipedia.org/wiki/German_submarine_U-864
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