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Old 13th Jan 2020, 5:31 pm   #502
emeritus
Dekatron
 
Join Date: Jan 2012
Location: Brentwood, Essex, UK.
Posts: 5,316
Default Re: Vintage Christmas Tree lights

My set of 12 x 20V fairy lights that I extended to 16 a couple of decades ago so they run at 15V, had worked faultlessly with no bulb failures. However, a couple of days before packing them away, a bulb blew. No problem, I have a couple of spares. The one I fitted blew too the following day, likewise with its replacement (my last). Ok, time to fit one of my 12V 200mA bulbs that work, with a warm yellow glow. Blow me down, but another bulb blew in a different place, this time leaving the string lit. Probably one of a set I got from Woolworths in the 1990's when they were designed to do this. I recalled having read that the filament might actually be intact, that the shorting element might have operated in error, and that it might be possible to make the lamp work by passing a high current through the bulb to fuse the shorting element. Nothing to lose, so dug out a couple of large electrolytic capacitors, connected them across my bench supply, set it to 20V, and connected to the bulb. Hey presto, it worked! I think that the ones that had blown were from sets of spares I had bought new in the 1980's and 90's. The 1950's originals just keep soldiering on. Now I must get some spares for next year, there seem to be plenty on Amazon at reasonable prices.
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