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Old 30th Nov 2016, 9:47 pm   #61
Lucien Nunes
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Default Re: Mercury Arc Rectifier? Where to start

Ooo! A bulb! She's quite unusual, 40A rating with angled arms, not sure if she is the type used in the Unitarc Minor or whether more likely to have worked in an industrial setting.

Like the Nevelin mentioned earlier in the thread, this bulb has the raised cathode leadout which is quite helpful as it reduces the chances of a bulk mercury escape compared to a vertical one. It also makes it easier to build a support as all that is needed is a dished foam pad to sit on, and a 'headband' lined with something soft near the top of the bulb to hold her upright.

Get a spill kit but beware, many are a bit of a con and you can end up paying large sums of money for trivial contents, as they are targeted at box-ticking compliance-oriented managers who have one mercury thermometer in their department. My spill kit consists of various sponges, scoops and syringes, a bunch of amalgamating alloy wool, a few kg of sulphur and the same of calcium hydroxide. And some airtight containers to pack the debris in.

If you want to give her a bath, don't wash or wipe the printing as it can come off, just brush that part lightly with a paintbrush. Avoid any twisting or pressure on the endcaps and keep the mercury out of the (long, thin) dipper electrode arm, and she will be a happy bulb.
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Old 30th Nov 2016, 10:36 pm   #62
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Default Re: Mercury Arc Rectifier? Where to start

That is quite a thing!! I can imagine how elated you must be.
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Old 1st Dec 2016, 12:13 am   #63
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Default Re: Mercury Arc Rectifier? Where to start

It does look bigger out of the box! Looks as scary as handling some big old CRT's.

Just sat and read up about them, found it quite interesting, don't know why I've never looked into such things before!

Regards,
Lloyd.
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Old 1st Dec 2016, 12:19 am   #64
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Default Re: Mercury Arc Rectifier? Where to start

Well done! It's a fair old size of thing isn't it? Must weigh a fair bit too. Next challenge is to get it going!
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Old 1st Dec 2016, 2:51 am   #65
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Default Re: Mercury Arc Rectifier? Where to start

Any history on its earlier application, and any operating data/datasheet ?

Perhaps a nearby university chem lab has a mercury vapour detector and would welcome you paying them a visit (just to eyeball that valve!). Perhaps putting it over a Bunsen burner is a bit crude, but they may have a glass flask heater to test for changing emissions when the mercury and seals etc are warmed up (not too sure how else a vacuum test can be done - any ideas Lucien?).
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Old 1st Dec 2016, 6:58 am   #66
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Congratulations Steph! Xxxxxx!

A few transformers and chokes, an electromagnet for the start electrode, and you'll be in business!
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Old 1st Dec 2016, 7:26 am   #67
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Congratulations!
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Old 1st Dec 2016, 8:25 am   #68
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Default Re: Mercury Arc Rectifier? Where to start

It is quite heavy! I was panicking on the way home but she made it! The man who I got it off did a house clearance for a family who's grandad who past away and he was a projectonist so he thinks it was used in an old cinema, the badge is the Hackbridge and Hewittic Electric logo but reads Hewittic Rectifiers, I'm so happy the makers mark is still there even though it's not perfect you can still tell what it says.

She's quite mucky at the moment, does anyone know the best way to get her clean? I'm going to go over the logo with a brush as Lucien says but for the rest of the bulb would a normal glass cleaner be okay?

Regards
Steph
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Old 1st Dec 2016, 10:04 am   #69
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Don't see why not, provided it's a non-abrasive type!
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Old 1st Dec 2016, 10:33 am   #70
Lucien Nunes
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Vacuum test is best done by connecting up and seeing her working. Then you can not only say she has a vacuum but from the shape of the ionised path you can get a reasonable idea of the quality.

There was a very scary method called the 'click test' where you deliberately slurp some mercury into one of the arms and listen to the noise it makes when it hits the end - a sharp click indicates a hard vacuum! Of course it's an easy way to break the seal and knock the end off the arm, especially if the bulb was good to start with, so I don't recommend it and don't use it myself. I have had two bulbs fail, including an unused 150/6 with a perfect vacuum, when something similar to a click test happened during handling.

There is also the 'bubble test' which will only show if it is down to air, where you collect some mercury in an arm and pour it back into the pool while watching the surface for entrained bubbles of air escaping. It's not very conclusive and a lack of bubbles does not always indicate a viable bulb.

Glass cleaner is OK, keep it well clear of the printing (don't forget the serial number between the arms). Work around the logo with a wet cotton bud. If it has run hot for a long time the print might be reasonably water-fast but you can never tell.

If she is from a cinema projector arc supply then I would guess she came from a Unitarc Minor equipment. However unit-type rectifiers operate at a fairly low voltage because there's no ballasting needed on the DC side, it's done reactively upstream of the transformer, so the PIV under load is only double the lamp arc volts. Therefore they often have bulbs with straight arms. The upright arms might have been to reduce the area of the bulb in plan though, rather than to avoid straight ion paths. Unfortunately I don't have any HH Unitarc literature to show what kind of bulb was used.

Alternative jobs she might have done include charging a central-battery emergency lighting system, or powering any DC plant that was retained after a public supply changeover from AC to DC.
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Old 1st Dec 2016, 11:25 am   #71
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Lucien, presumably straight arms are cheaper to make, and also give a slightly lower voltage drop too? I'm more than slightly interested in this project!
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Old 1st Dec 2016, 11:56 am   #72
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Default Re: Mercury Arc Rectifier? Where to start

Steph, are you familiar with Derby Makers? http://derbymakers.co.uk/

They have handy equipment like woodworking gear, a laser cutter, 3D printer, etc., that might be useful for constructing a display, and lots of helpful and knowledgeable folks whom I'm sure would be fascinated by that amazing bulb.
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Old 1st Dec 2016, 12:11 pm   #73
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Default Re: Mercury Arc Rectifier? Where to start

Quote:
Originally Posted by kalee20 View Post
Lucien, presumably straight arms are cheaper to make, and also give a slightly lower voltage drop too? I'm more than slightly interested in this project!
Something about your username suggested that you might be interested in this project!
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Old 1st Dec 2016, 12:28 pm   #74
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Default Re: Mercury Arc Rectifier? Where to start

Clean it with baby wipes, or wet wipes. Keeping clear of the markings as already advised.
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Old 1st Dec 2016, 2:09 pm   #75
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Default Re: Mercury Arc Rectifier? Where to start

Thanks for the advice! I'll post a before and after clean up after work
Regards,
Steph
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Old 1st Dec 2016, 2:17 pm   #76
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Default Re: Mercury Arc Rectifier? Where to start

I thought some may be interested in this little brochure I found online!
Regards,
Steph
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Old 1st Dec 2016, 2:31 pm   #77
kalee20
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Wow... I'd generally thought the working life is virtually infinite? 400 hours guaranteed isn't long!
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Old 1st Dec 2016, 3:42 pm   #78
Lucien Nunes
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I'm sure many later bulbs ran well into tens of thousands of hours, I know of some that have almost certainly done >50k. But that catalogue is from 1921, when materials and manufacture techinque had not yet had the R&D input from mass commercial use of valves. I expect that even those bulbs vastly exceeded the 400h on average, although I do not know what failure mechanism was likely to be responsible for failure at 500h for example.

Many of the unserviceable bulbs I have come across have failed through either physical damage, overload or seal leakage of unidentified cause. There was the possibility of catastrophic damage by reverse conduction and flashover and surge arrestors were often fitted to avoid high transient voltages reaching the bulb but I doubt that was common. Theoretical internal wear-out mechanisms are erosion of the dipper and anode ablation, which will depend on start frequency and loading, and although I have seen bulbs with apparently worn dippers and a slick of carbon on the pool, it did not stop them working. Tilt- and magnetostriction-start types do not even have a dipper to wear out.

Last edited by Lucien Nunes; 1st Dec 2016 at 3:48 pm.
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Old 2nd Dec 2016, 12:31 am   #79
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Ahhh, if it wasn't for MAR's, and the ability to phase regulate them...
http://durenberger.com/documents/XERAROTH.pdf

Some serious power flowing in that link!
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Old 2nd Dec 2016, 12:46 am   #80
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Default Re: Mercury Arc Rectifier? Where to start

Wow, Stephanie, You really have got everyone fired up with this fantastic project There can be few instances where a new member has generated so much interest with their first thread!!
I love Lucien's obvious passion for MAR's (and extensive in-depth knowledge on the subject) You should also read some of his threads on 'organ rescue'- makes fascinating reading!!
I'm sure we are all eagerly "tuning in for the next exciting instalment" to see what happens next
One thought did occur- how did you transport it home? Please tell me you didn't carry it home on the bus
That's what I love about this forum: every member has a real passion for some part of our technological past.
Can't wait for the next part!
Cheers Nick
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