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Sets, Parts and Service Information Wanted (private buyers only, no swaps) If you need help obtaining components, sets or equipment, post a message here. Private buyers only - no traders. No swaps.

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Old 5th Apr 2020, 11:05 am   #1
Jacob_Pearson
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Default Wanted: Mercury Arc Rectifiers

I am looking for some Mercury Arc rectifiers. The single phase type with the control gear contained in a unit that would be used to run Carbon arc lamps in a Cinema. The Hewittic Unitarc, Nevelin or Nevelector units would be ideal.

I hoping to use pair of original Mercury Arc rectifiers to run the carbon arcs lamps on my Gaumont-Kalee 35mm projectors, that I am using as part of a vintage cinema project at home.


Please let me know if you have any or know of any old cinemas that still have them intact in the building.


Attached is an advert for the Hewittic units.
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Old 5th Apr 2020, 2:17 pm   #2
Techman
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Default Re: Wanted: Mercury Arc Rectifiers

We had one in a big cabinet like the one shown in your advert picture at work back in the 70s, I think I may have an old B&W photo of it somewhere that I took at the time.

I had a small one at home for a few years, but very sadly decided to get rid of it as it was too much of a liability to keep in an ordinary domestic home.

You probably realise that these things can't be sent through the normal post/courier services.
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Old 5th Apr 2020, 8:52 pm   #3
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Default Re: Wanted: Mercury Arc Rectifiers

I did have tens of arc rectifiers at one time, however have off loaded all the ones I no longer want and am down to a manageable couple.
Ralf Jaeckel in rosenheim, http://www.quecksilberdampfgleichrichter.de or Lucien Nunes on here are probably your best bet at a lead......
there is a chap called Chris from Newport that had a few working projectors, not sure if he is on here, but usually has a stall at NVCF
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Old 5th Apr 2020, 9:16 pm   #4
The Philpott
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Default Re: Wanted: Mercury Arc Rectifiers

I have sent you a private message Jacob.
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Old 6th Apr 2020, 12:34 am   #5
AC/HL
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Default Re: Wanted: Mercury Arc Rectifiers

Quote:
Originally Posted by Megatron View Post
there is a chap called Chris from Newport that had a few working projectors, not sure if he is on here, but usually has a stall at NVCF
Now renamed RetrotechUK: https://www.retrotechuk.com/
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Old 9th Apr 2020, 1:54 pm   #6
Jacob_Pearson
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Default Re: Wanted: Mercury Arc Rectifiers

Quote:
Originally Posted by Techman View Post
We had one in a big cabinet like the one shown in your advert picture at work back in the 70s, I think I may have an old B&W photo of it somewhere that I took at the time.

I had a small one at home for a few years, but very sadly decided to get rid of it as it was too much of a liability to keep in an ordinary domestic home.

You probably realise that these things can't be sent through the normal post/courier services.

It would be interesting to see that photograph if you can find it.

A shame that you had to get rid of your unit.

I am happy to travel to collect if I can find some rectifiers. I have transported and used one in the past, so know how to handle/transport them correctly.

Last edited by Jacob_Pearson; 9th Apr 2020 at 2:03 pm.
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Old 9th Apr 2020, 2:02 pm   #7
Jacob_Pearson
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Default Re: Wanted: Mercury Arc Rectifiers

Quote:
Originally Posted by Megatron View Post
I did have tens of arc rectifiers at one time, however have off loaded all the ones I no longer want and am down to a manageable couple.
Ralf Jaeckel in rosenheim, http://www.quecksilberdampfgleichrichter.de or Lucien Nunes on here are probably your best bet at a lead......
there is a chap called Chris from Newport that had a few working projectors, not sure if he is on here, but usually has a stall at NVCF

Thanks for the leads. I messaged Lucien a few months back. He said he would keep an eye out for me.
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Old 9th Apr 2020, 7:54 pm   #8
Ed_Dinning
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Default Re: Wanted: Mercury Arc Rectifiers

Hi Jacob, I may have some of the "small stuff", mercury vapor rectifiers if of interest.

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Old 10th Apr 2020, 10:20 am   #9
thermionic
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Default Re: Wanted: Mercury Arc Rectifiers

Hi Jacob.

This may be of interest. It was there 12 months ago in an old cinema that I was due to work on. Unfortunately, the project has been put on hold indefinitely so it may still be there. Iíll make some enquiries and find out.

Cheers. SimonT.
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Old 10th Apr 2020, 11:29 am   #10
Lucien Nunes
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Default Re: Wanted: Mercury Arc Rectifiers

Simon... I seem to recognise that unit. I thought it was lost during construction work years ago, but if it is not usable by Jacob (it's 3-phase 415V input) it's definitely worth keeping tabs on it and ensure it does not get scrapped. An interesting feature it that it uses pinch ignition rather than the much more common dipper. I have one complete Nevelin pinch-ignition installation in sight (formerly suppling a DC motor) which has a damaged bulb, but might still be worth rescuing as there is at least one such bulb in preservation looking for a set of control gear. A dual-bulb unit gives a certain amount of redundancy!
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Old 10th Apr 2020, 7:23 pm   #11
duncanlowe
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Default Re: Wanted: Mercury Arc Rectifiers

No idea if there's any way of tracing further, but there's a cinema in Nuneaton that is still there though out of use for many years. It was a bingo hall for many years before closing, but before that, I know for certain it had a mercury arc rectifier as I saw it working. I can't see that they would ever have got round to removing it, and photos I've seen of a few bits of the interior many years after closing show a lot of the original projection stuff still lying around. It was latterly known as Ritz Bingo, having been the Ritz cinema and ABC. I believe it was fairly recently bought for some project but as I no longer live locally can't give any more information.
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Old 10th Apr 2020, 11:01 pm   #12
kalee20
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Default Re: Wanted: Mercury Arc Rectifiers

Interesting that the rectifiers have 3 arms not 6, does this imply it's a 3-phase half-wave set (with associated increase in ripple, plus giving the transformer a harder time?

Quote:
Originally Posted by Lucien Nunes View Post
An interesting feature it that it uses pinch ignition rather than the much more common dipper.
Exposing my ignorance! But what's pinch ignition? I've read about dipper and tilt start, but this is a new one!
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Old 11th Apr 2020, 12:49 am   #13
Lucien Nunes
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Default Re: Wanted: Mercury Arc Rectifiers

3-phase MARs were quite common, especially in drive applications where ripple was of minimal importance and the extra complexity of a 6-pulse 2-group secondary and interphase transformer was not justified on grounds of effiiciency. A 3-phase full-wave circuit suffered from voltage droop due to conduction overlap caused by leakage inductance, so in practice a 3-phase bulb fed by a zig-zag winding (to cancel the DC component) achieved similar utilisation of the transformer.

A bulb configured for pinch ignition has a second small liquid pool connected to the cathode pool by a narrow neck of mercury, just as for tilt. In Simon's picture, the ignition limb of the closer bulb is visible bottom left, attached to the bulb at a steep angle. A heavy low-voltage transformer winding, connected between the two pools, drives sufficient current through the mercury isthmus at startup to produce a radial force that implodes or 'pinches' it into droplets, interrupting the circuit and starting the arc. The ignition circuit is broken by a contactor that responds to load current in the usual way. Pinch and tilt setups offer the theoretical advantage that there is no dipper electrode to wear out. I have seen worn dippers but have no information on how common this was as a failure mode in real applications, so I am unsure whether the extra cost and complexity was justified.
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Old 11th Apr 2020, 2:46 am   #14
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Default Re: Wanted: Mercury Arc Rectifiers

When I was at the Adelphi Theatre in 1985 the DC control gear was being stripped out (me and a colleague dismantled some of it) but I did get the chance to see a "Mekon" mercury arc rectifier running before it all went. What a beautiful sight it was. Carbon arc spots had been used for the last time only a few years before, but by then we were using 1000W CSIs (Strand Pattern 765) for follow spots. Nowhere near as romantic as a carbon arc Super Trouper.
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Old 11th Apr 2020, 2:25 pm   #15
Lucien Nunes
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Default Re: Wanted: Mercury Arc Rectifiers

Quote:
in 1985 the DC control gear was being stripped out
Had I started on my project to replicate and conserve a large prewar theatre / cine-variety electrical system just a decade earlier, it would have been 100 times easier.

Quote:
by then we were using 1000W CSIs (Strand Pattern 765) for follow spots
If you want to relive those days, buy your stock of replacement lamps now. I believe GE have just manufactured the last batch.

But we are drifting from Jacob's quest for Unitarcs. As a memory jogger, these compact units, often with single-phase supply, were placed alongside or under each lamphouse and powered it via a direct connection with no DC control gear. By supplying only one lamp and striking along with the carbons, it was possible to implement the current control magnetically on the AC side, so that the rectifier worked at arc volts rather than a fixed voltage. This both reduced the power consumption (due to lack of resistances) hence transformer size, heat dissipation, and the PIV requirement of the bulb making that more compact too. They had limitations but were ideal for HiLo lamps.
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Last edited by Lucien Nunes; 11th Apr 2020 at 2:31 pm.
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Old 11th Apr 2020, 9:31 pm   #16
kalee20
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Default Re: Wanted: Mercury Arc Rectifiers

Quote:
Originally Posted by Lucien Nunes View Post
A bulb configured for pinch ignition has a second small liquid pool connected to the cathode pool by a narrow neck of mercury, just as for tilt... A heavy low-voltage transformer winding, connected between the two pools, drives sufficient current through the mercury isthmus at startup to produce a radial force that implodes or 'pinches' it into droplets, interrupting the circuit and starting the arc. The ignition circuit is broken by a contactor that responds to load current in the usual way. Pinch and tilt setups offer the theoretical advantage that there is no dipper electrode to wear out.
Thanks, Lucien!
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Old 14th Apr 2020, 9:03 pm   #17
Jacob_Pearson
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Default Re: Wanted: Mercury Arc Rectifiers

Thank you to everyone for their input.

I have now found a matching pair of single-phase unitarc style Nevelin Mercury Arc rectifiers. I found one unit locally, and have it home. I will upload some photos / bulb type later. I would really appreciate if anyone can provide information / literature relating to this model of unit and bulb. The other rectifier is located a few hours drive away, so I will hopefully be collecting that once the UK lockdown is relaxed. In the meantime, I aim to get the unit I have tested and operating with one of my carbon arc projector lamps.

I am now on a quest to find spare bulbs to keep on hand for these units. I will make a separate wanted thread with a photo and model number of the bulb type.
Quote:
Originally Posted by thermionic View Post
Hi Jacob.

This may be of interest. It was there 12 months ago in an old cinema that I was due to work on. Unfortunately, the project has been put on hold indefinitely so it may still be there. I’ll make some enquiries and find out.

Cheers. SimonT.
Simon,

It would be great if you can pursue that dual-bulb unit further. I have another cinema enthusiast friend who is also looking for Mercury Arc rectifiers, and has a three-phase supply. This might be suitable for him.
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Old 16th Apr 2020, 8:00 pm   #18
thermionic
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Default Re: Wanted: Mercury Arc Rectifiers

Hi Jacob.

Iíve messaged my contact to enquire whether itís still in situ, but havenít heard back from him yet.

Cheers. SimonT.
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Old 16th Apr 2020, 9:51 pm   #19
Lucien Nunes
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Default Re: Wanted: Mercury Arc Rectifiers

Great news! I have the brochure for the Nevelector which I could scan and send. I do not have any technical info on paper but I know the units inside out and can help if needed.
Suggested startup checks:
Inspect the bulb carefully for cracks around the seals that may have occurred in transit. Check the clamps are tight but not excessively so. NEVER APPLY ANY TWISTING FORCE TO THE CLAMPS as this is the most likely cause of seal failure. Remove any grease / heavy dirt from the main arms so that it does not burn on, but avoid scratching the glass especially near the seals.
Level the bulb at least passably - how critical it is depends on the condition of the dipper. Dipper tip should be about 1/4" above mercury.
When re-fitting the dipper coil, set the pole pieces either side of the steel slug in the dipper spring. If you forgot to remove it, and the bulb is still in one piece, have a beer to celebrate.
Check the operation of the ignition cutout contactor at least manually, making sure it breaks both poles.
Disconnect the small block electrolytic capacitor on the output.
Check that the Metrosil stick is seated in its clips (at the studs where the anode pigtails terminate). This may give off a smell of hot dust when first run.
Switch on. You should have full unloaded AC volts across the DC output. Don't worry, that's only the ignition circuit, it will turn to DC by magic when you strike the lamp!
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Old 18th Apr 2020, 1:31 am   #20
Jacob_Pearson
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Default Re: Wanted: Mercury Arc Rectifiers

I have now tested the rectifier with one of my carbon arcs. The Mercury arc runs nicely and all control gear and contacts are in great condition. The cooling fan is unfortunately not working and is stiff to turn, so don't want to run the rectifier for long until this is sorted. Attached are photos of my unit - sorry they are quite dark. The bulb type is a Nevelin Single Phase WD1040N.

Quote:
Originally Posted by thermionic View Post
Hi Jacob.

Iíve messaged my contact to enquire whether itís still in situ, but havenít heard back from him yet.

Cheers. SimonT.
Much appreciated - thanks Simon.


Quote:
Originally Posted by Lucien Nunes View Post
Great news! I have the brochure for the Nevelector which I could scan and send. I do not have any technical info on paper but I know the units inside out and can help if needed.
Suggested startup checks:
Inspect the bulb carefully for cracks around the seals that may have occurred in transit. Check the clamps are tight but not excessively so. NEVER APPLY ANY TWISTING FORCE TO THE CLAMPS as this is the most likely cause of seal failure. Remove any grease / heavy dirt from the main arms so that it does not burn on, but avoid scratching the glass especially near the seals.
Level the bulb at least passably - how critical it is depends on the condition of the dipper. Dipper tip should be about 1/4" above mercury.
When re-fitting the dipper coil, set the pole pieces either side of the steel slug in the dipper spring. If you forgot to remove it, and the bulb is still in one piece, have a beer to celebrate.
Check the operation of the ignition cutout contactor at least manually, making sure it breaks both poles.
Disconnect the small block electrolytic capacitor on the output.
Check that the Metrosil stick is seated in its clips (at the studs where the anode pigtails terminate). This may give off a smell of hot dust when first run.
Switch on. You should have full unloaded AC volts across the DC output. Don't worry, that's only the ignition circuit, it will turn to DC by magic when you strike the lamp!
Thanks for the guide Lucien - lots of helpful info there. Yes please send the Nevelector brochure scans. They will be very interesting to see/read. I will message you my email address to send them to.
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