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Author Topic: Using AC lamps to replace Xenon Jonathan Wood Expert Film Handler Posts: 206 From: Oxfordshire, United kingdom Registered: Jan 2008 posted 05-17-2013 10:52 AM                     Hi, I have a cx 900 cinemeccanica lamphouse that I would like to convert to a halogen lamp. Has anyone any experience using tungsten AC lamps in place of a xenon? There are plenty of hi powered AC lamps out there 800w 2kw etc that would give a decent output but would there be a flicker problem ie 50hz with a2 blade shutter? It would avoid a transformer and DC lamps don't generally get above 400 w as far as i can tell. I seem to remember B&H used 1000w AC lamps in their old 16mm machines but was this with a 3 blade shutter? Any advice greatly appreciated ! Jon  |  IP: Logged Dave Macaulay Film God Posts: 2321 From: Toronto, Canada Registered: Apr 2001 posted 05-17-2013 12:58 PM                     Tungsten filament lamps don't flicker enough at line frequency to cause a problem. The filament can't cool down enough in 1/50 sec to make much difference in light output. Some line frequency flicker can be measured from a lamp - how much depends on the thermal mass of the filament - but you won't see it on screen.  |  IP: Logged Jonathan Wood Expert Film Handler Posts: 206 From: Oxfordshire, United kingdom Registered: Jan 2008 posted 05-17-2013 01:33 PM                     Thanks Dave, that's what I thought, but might there be an slow pulsating as the 1/48 shutter cycles against the 50hz mains? Makes you wonder why more people don't use ac lamps instead of the hassle of dc?  |  IP: Logged Sean McKinnon Phenomenal Film Handler Posts: 1712 From: Peabody Massachusetts Registered: Sep 2000 posted 05-17-2013 08:05 PM                        Color temperature? Efficiency? Cost per operating hour?  |  IP: Logged Lindsay Morris Expert Film Handler Posts: 233 From: Darlington, WA, Australia Registered: Sep 2002 posted 05-17-2013 08:46 PM                     Johnathan, I use a 600W 120V type BHC/DYS/DYV in my screening room setup in an old carbon arc lamp housing with a 10" mirror and the light onto a 12 foot wide screen is quite good. NO flicker as others have posted. I had a transformer specially wound that was 240V in and fitted with 6 taps on the secondary side to give me 118v, 120V, 122V, 124V, 126V & 128V (at 240V IN) and switchable from a HD rotary switch under the lamphouse. The lamp is also preheated by a 30V tap that just makes the filament glow a slight orange colour and the tap is switched out as the Lamp switch is operated (SPDT switch there). Preheating stops the switch on shock and I rarely have a lamp blow on switch on. The adjustable taps allow the brightness to be ramped up for dull prints and colour temp is a bit yellow as compared to xenon but good enough for my needs. I think your lamphouse is a Vertical style xenon and due to the cut out of the mirror top and bottom you will lose a lot of light as a couple of my mates found out when they tried to insert a incandescant lamp into a vertical xenon lamphouse. But for small screen sizes it was OK..just. The 600W lamp I chose has a very nice thick filament running horizontally and on the preheat setting I could accurately focus up the filament image onto the back of the gate by using the mirror controls. Thus it neatly fills the entire aperture area for either scope or widescreen so as much light as possible is squeezed thru. I very carefully made sure that the C/L of the filament was exactly on the optical axis where the carbons used to burn so if you do the same with a xenon lamphouse you should be sweet and get reasonable results. There was a screening room in Perth a few years back that used 36V 400W lamps in the 2 machines onto a 22 foot wide screen and the results there were also quite good. But they DID over run the lamps by about 10% and used to have a few failures on switchover. Have fun.  |  IP: Logged Jonathan Wood Expert Film Handler Posts: 206 From: Oxfordshire, United kingdom Registered: Jan 2008 posted 05-18-2013 10:44 AM                     Lindsay, thanks for the advice , kindlyappreciated Sean, I meant in a home theatre environment , not theatrical . Cheers  |  IP: Logged Jack Ondracek Film God Posts: 2348 From: Port Orchard, WA, USA Registered: Oct 2002 posted 05-18-2013 01:01 PM                        quote: Dave Macaulay Tungsten filament lamps don't flicker enough at line frequency to cause a problem. The filament can't cool down enough in 1/50 sec to make much difference in light output. Some of you might recall the exciter lamps that were made to run on AC, or unfiltered DC. IIRC, they ran a volt or so lower, but had higher current ratings. The filaments were noticeably thicker. Using them resulted in less hum in the system. One of the drive-ins I used to work for had a Motiograph DC supply (merc tubes!). Very good sound. Switching to the "emergency supply", an old AC transformer, kept you on the screen, but there was some hum. Probably the worst application I ran into was an indoor house that used a battery charger for their exciter supply!  |  IP: Logged Jonathan Wood Expert Film Handler Posts: 206 From: Oxfordshire, United kingdom Registered: Jan 2008 posted 05-18-2013 01:17 PM                     Lindsay, thanks for the advice , kindlyappreciated Sean, I meant in a home theatre environment , not theatrical . Cheers  |  IP: Logged Ben Wales Jedi Master Film Handler Posts: 602 From: Southampton. England Registered: Jul 99 posted 05-18-2013 04:59 PM                     Most Home (35mm projectors) I have seen and used use a 35v 400w Quartz Lamp. I use a Xenon Lamp at home as that still has a better Colour Tempature than a Quartz Lamp.  |  IP: Logged Jonathan Wood Expert Film Handler Posts: 206 From: Oxfordshire, United kingdom Registered: Jan 2008 posted 05-19-2013 02:14 AM                     Those 36v 400w lamps are still around 3.4k I think so will always be ' yellower' than xenon which is daylight balanced, plus you need a transformer. There are DXX 800w/230AC bulbs which I am going to try out at home , they are cheap and normally used in 'Red Head' photographic lamps . The reflectors from these lamps might be a better bet than the mirror in a vertical lamphouse as as Lindsay points out , there would beca lot of light loss.  |  IP: Logged Ben Wales Jedi Master Film Handler Posts: 602 From: Southampton. England Registered: Jul 99 posted 05-19-2013 03:44 PM                     I would use these type of Lamps rather those as they don't last that long!. 240v 1000watt Quartz Keep the Orignal Lamphouse Mirror and re-focus the Quartz Lamp Holder in relation to the Mirror for a flat light.  |  IP: Logged Lindsay Morris Expert Film Handler Posts: 233 From: Darlington, WA, Australia Registered: Sep 2002 posted 05-19-2013 09:12 PM                     Jonathan, Ben's suggestion of the 1000W lamp is far better than the lamp you were thinking of as the filament is much more compact and can thus be focused down more effectively than the rather large long tube like filament of the 800W lamp you were thinking of. That type of lamp is more suited to a floodlight situation rather than projection which is better when point sources of light are used. IE the old carbons, xenon etc. Colour temp of the 36V 400W lamp is quite good as it is a halogen style as is the one that I use. I went to the thicker filament style so I could over run it a bit without early failures whereas the 240V lamps having far thinner diam wire inside are not overly happy when run over voltage. If you wanted to see a VERY bad example of inter action between the projector shutter and the light source look no further than the old mains powered AC arc supplies. The carbons could not really maintain a constant flood of light as the mains frequency cycled thru and the end result on screen was a slow pulsing of the light on screen from 50Hz supplies. VERY noticeable on the edges of the screen. In most sites that I encountered years ago the trick we used was to make the motor pulley slightly larger in diameter so the machine ran at about 26FPS and then NO pulsing was evident. The most common way of increasing the motor pulley diam was to wind on a few turns of the old cloth type insulation tape and thus run the belt higher up the pulley cheeks...rough and ready but in most cases these were often portable sites that had plant that was moved from town to town. Hence the AC arc supplies in the first place.  |  IP: Logged Jonathan Wood Expert Film Handler Posts: 206 From: Oxfordshire, United kingdom Registered: Jan 2008 posted 05-20-2013 01:09 AM                     Thanks Lindsey and Ben, Yes I was thinking of trying a lamp with a smaller filament for just that reason. The lamp Ben suggested , after a quick look, seems pretty hard to get hold of though. Lindsey, do you think the pulSating will be noticeable then? The machine is inverter run so I could run at 25fps which should clear it? Thanks guys  |  IP: Logged Lindsay Morris Expert Film Handler Posts: 233 From: Darlington, WA, Australia Registered: Sep 2002 posted 05-20-2013 03:17 AM                     Jonathan. I doubt that you will see any pulsating with an AC lamp doing the work...but carbons are another kettle of fish. A couple of home screening setups nearby use 240V 1000W lamps sited exactly where the carbon tips used to sit and the results on screen are fine. Another 240V 1000 W lamp that you might find is type A1/207 which has and Octal type base and was used in the Bell & Howell 652 machines prior to them shifting to the 24V 250W lamps. Another choice if you have some theatrical types about is the 240V 1000W P28s base which is a prefocus base where you push the lamp in and turn slightly to lock it in...they used to be used in spot light units for stage lighting. Seen BOTH lamp types used in home cinema setups and light is good. If you use a 240V lamp they last way longer if you can arrange a preheat circuit...like start them on about 50V and then go to the full 240V when about to screen...virtually NO filament stress that way.  |  IP: Logged Jonathan Wood Expert Film Handler Posts: 206 From: Oxfordshire, United kingdom Registered: Jan 2008 posted 05-20-2013 03:27 AM                     Thanks Lindsey, that's really helpful! Appreciate it! Cheers Jon  |  IP: Logged

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