Film-Tech Forum ARCHIVE: Cleaning silver contacts in a carbon arc lamphouse

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Posted by William Hooper (Member # 71) on 09-15-2003, 03:58 AM:

There are some areas of tarnish on the silver contacts in a lamphouse that I just can't get rid of. What recommendations are there for cleaning them completely?

Posted by John Pytlak (Member # 331) on 09-15-2003, 08:22 AM:

Does the tarnish cause a problem with the electrical contact, or is it just an "appearance" issue? When I worked at the drive-in, we just used a round stiff-bristled "bottle" brush daily to clean the inside of the contacts where the carbon rotated.

Posted by William H. Ward (Member # 1797) on 09-15-2003, 10:32 AM:

Oops, made a mistake. See my new post "cleaning contacts." Should have been a relpy instead of a new post.....

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When I was a booth operator, cleaning contacts was a daily per shift requirement. For Strong rotating lamps, we used just a brush (tubular). Oxides of carbon, which was the residue seen, were good conductors and posed no problems. Ashcraft lamp silver contacts were cleaned with powdered Bon Ami. On your cloth, work up a good paste, scrub, let dry and polish it off. We used the same stuff on reflectors. Worked great.

[ 09-15-2003, 01:56 PM: Message edited by: Daryl C. W. O'Shea ]

Posted by Jim Spohn (Member # 1547) on 09-15-2003, 10:54 AM:

John is right on the money! If the blemishes are tarnished black, then they are silver oxcide (which is a better conductor than silver) don't worry about them. However if the marks on the contacts are burned and pitted, the only thing you can do is remove material until things are flat again. Filing out the contacts can be done if EXTREEMLY careful not to go too far. once the contacts get too thin they: A) Won't make good contact B) Won't dissapate the heat well. For the most part if the contacts are working ok but just look crappy, leave them alone.
I screwed up and cleaned mine with a file and improved them to the point that they were totally useless (I'm learning). I ended up casting new ones from coin silver and machining. Good luck

Posted by Dick Prather (Member # 1136) on 09-15-2003, 04:47 PM:

As stated above I used to use a round stiff bristle brush every day as part of routine lamp cleaning. We used Bon-Ami every couple of months or only when needed. The main thing we did was wipe the dust off the carbon with a small towel everytime we put a new stick in. The dust acts like a fine gringing compound on the silver contacts. That really helped prolong the contacts. I got the hint from a senior operator at one of the first run houses and it seemed to work great.

The regular operator had been using Bon-Ami daily and we he went through contacts once or twice a year. After using the brush and wiping the carbon we went to almost no changes in the six years I was there at the DI.

Posted by William Hooper (Member # 71) on 09-16-2003, 12:16 AM:

Thanks everyone!

It's a black, tarnished area inside the contacts which is not removed when polishing with Comet paste on a wet cloth, so I assume it is a pitted area.

These areas are mostly scratch-like, elongated in the direction of the carbon rod, so that looks like it jibes with Dick Prather's information about dust on the carbon acting as an abrasive - they could have begun as scores from carbons being slid in.

I guess dealing with the tarnish which can't be removed would be decided by whether silver oxide accelerates deterioration of the rest of the silver beneath it, or will it like aluminum oxide prevent it?

The theater does not show films all the time - they'll run for consecutive weekends for a while, then not run any for a month, then run a matinee & midnight movie one weekend, etc., so "routine maintenance" is usually a new routine that must be devised.

Posted by Robert Throop (Member # 61) on 09-16-2003, 05:26 PM:

I worked in a house that had Super Core Lites. We cleaned the contacts daily with Bon Ami which is the recommended method in the Ashcraft manual. The first set of contacts lasted at least ten years.

Posted by Edward Jurich (Member # 1787) on 09-16-2003, 08:37 PM:

Hey Bill, you can resilver bad areas. Check and see what's used in transmitter re-slivering, Geoff might be able to get that info for you.

Posted by Gerard S. Cohen (Member # 994) on 09-16-2003, 08:59 PM:

I've only had very limited experience with those beautiful Ashcraft lamphouses with revolving, silver, chain-driven positive carbon jaws.

So permit me to ask, "Are the 'silver' jaws real silver,
or, like the positive carbon posts in the Peerless Magnarc lamps,
made of so called German silver? German silver is not silver, but a nickel alloy also called monel metal or alpaca. It resists
tarnishing and was often used in Europe for cookware and eating utensils, as it gleams and resists corrosion, yet transmits heat well. It must also be a good conductor of electricity.

So which was used for Ashcraft jaws?

Posted by Gordon McLeod (Member # 33) on 09-16-2003, 09:44 PM:

They are reel silver

Posted by William Hooper (Member # 71) on 09-17-2003, 12:21 AM:

These are Ashcraft Core-Lites, with revolving positives.

#1's contacts seem to be sort of non-standard, almost like they were whittled from a chunk of solid silver.

#2 has an "11mm" factory-looking stamp on them. #2's also have a spot near the back where it looks like the negative collided with them (the negative was somehow in crooked?), & are slightly melted. There are a few sort of golden, brass-looking spots there.

Ed: Great tip!

Posted by John T. Mellor (Member # 468) on 09-17-2003, 09:19 PM:

We always used Bon Ami when it was time to do a real good cleaning . but we also cleaned them every day to get rid of the dust . We also used to put the next few days rods in the lamphouse to make sure they were dried out. [one of my old employers bought Le Arto carbons ]if you know about them you know why we cooked them befotre we used them.
I ran a lot of Ashcraft 13.6 mm , but the best was the Perless Hy-candescent ,if you know about them then you worked a great lamphouse.
P.S. I still have a set [1] 13.6 mm Ashcraft contacts never ben used