[Shop-talk] Lamp voltage

[Jimmie Mayfield]

3.5V x 35 lights in series = 122V so that part looks right.

1. How does the resistance of the new bulbs compare to the original 
(working) bulbs?

2. Might be worthwhile to feed 3.5V from a bench power supply across a 
fresh bulb to see if it burns out just as quickly as when plugged into 
the string.  You could also use batteries but it might be trickier to 
hit 3.5V.  Three NiMH batteries in series would yield 3.6V which ought 
to be close enough but you have to be careful not to use them straight 
off the charger since initially they'll be at 1.4V per cell.

3. You said you didn't notice the new bulbs overly bright before they 
burn out.  I wonder if they're really burned out or if the shunt at the 
bottom of the bulbs are for some reason causing a premature short 
circuit?  Using a magnifying glass, can you tell if the filaments are 
really separated?

J


On 11/27/22 17:36, Karl Vacek wrote:
> Shop content - as soon as I get the Christmas tree done I can go back 
> to the shop and work on something.
>
> We have many strings of Christmas lights on the tree. Almost all are 
> 30 year old plus Silvestri 35-light series strings.  Silvestri calls 
> for 3.5 volt replacement bulbs.  Replacement bulbs were getting scarce 
> locally so I ordered some from an Amazon seller, and some from a place 
> that specializes in hard to find items.  They're of two brands, all 
> 3.5 volt for 35-light sets.  Every one I install lights for a second 
> and burns out immediately.  They don't look overly bright as if they 
> were for a lower voltage.  Once burned out the string still stays lit 
> because they have the same jumper as the originals.
>
> What am I missing?
>
> Thanks !
> Karl
>
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