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There is a bulb in a firehouse in New York that (check memory) has
been running since the early 1900s, dimly, but continuously. Reason? They are running it at quarter voltage and it never gets that cold current spike that will kill it. Actually, according to http://www.snopes.com/science/lightbulb.asp it is in a firehouse in Livermore CA, since 1901 and is still (as can be seen on the real-time lightbulb-cam http://www.centennialbulb.org/photos.htm ) ON! It has been off and on a few times, and they make no mention of reduced voltage. - Steve On Thu, 22 Mar 2007 09:11:44 -0700, "RST Engineering" wrote: Or you could do it the right way and design a switching regulator with filtering for noise so that one output goes from x to y with control rotation, another from w to z, and still a third (inverse) output from v to u. The reason you don't start at 0 and go to + supply is that most lamps will last thousands of hours if they are prewarmed before running them up to ratings. There is a bulb in a firehouse in New York that (check memory) has been running since the early 1900s, dimly, but continuously. Reason? They are running it at quarter voltage and it never gets that cold current spike that will kill it. The second output starts at some low warming voltage but only goes up so far so as to not blind you when the first output goes nearly to the positive rail. You also need an inverse dimmer for lights that need to be bright during the day (marker, warning, etc.) but dim at night. Single control gets all three set correctly. Jim wrote in message ... Mike Spera wrote: The 2 VOR/ILS indicators are internally lit as is the VC compass and clock. These are all running off the one lone factory dimmer. On full, the indicator lights will illuminate the cabin, so I run them way down at night. I wonder if it would be possible to install lower-wattage lamps in the VOR/ILS indicators, or install a (fixed) resistor or diode in series with the existing lamps in the indicators. This would let you turn the dimmer knob up higher and have more light on your other instruments, without the indicators blinding you. A fixed resistor can be sized to give you pretty much whatever voltage drop you want. You'll probably need a "power" type rated for at least a few watts, and it needs to be mounted where it can get hot. If you really want to be fancy, get one of the ones that comes in a finned aluminum case with mounting lugs so it can be bolted down. |
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On Thu, 22 Mar 2007 09:11:44 -0700, "RST Engineering"
wrote: wrote in message ... [ too-bright VOR/ILS indicators] I wonder if it would be possible to install lower-wattage lamps in the VOR/ILS indicators, or install a (fixed) resistor or diode in series with the existing lamps in the indicators. Or you could do it the right way and design a switching regulator with filtering for noise so that one output goes from x to y with control rotation, another from w to z, and still a third (inverse) output from v to u. Well, _you_ could do it the right way over the weekend. _I_ could do it the right way after a couple of trips to Frank's Transistor Barn for another 1-lb bag of MOSFETs to replace the ones I would blow up. ![]() the general case, IMHO, installing a lower-powered lamp is something any repair station should be able to do, and installing an inline resistor or diode is something that most repair stations could probably do. Also, I know you mentioned filtering, but "switching power supply" and "AM radio" makes me a little nervous. The reason you don't start at 0 and go to + supply is that most lamps will last thousands of hours if they are prewarmed before running them up to ratings. I know some dimmers for stage use do this, but there, I think the "warming" current that flows even with the knob on 0 is there to get the lamp to respond faster when you suddenly turn up the knob. On AC, lamps also last longer if switched at the zero crossings of the waveform. Matt Roberds |
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