Can someone help me identify this bulb?

Thread Starter

stormBytes

Joined Jan 26, 2010
41
I pulled this from a nightlight, the kind that plugs into a wall outlet. I didn't really troubleshoot it part by part; I'm assuming its a bad bulb only there's some leftover solder on parts of the bulb and I can't make out what it is so help would be appreciated. The new variety are all LED and well, my mom prefers the incandescent. Thanks!
 

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elec_mech

Joined Nov 12, 2008
1,500
Looks like a mini bayonet base. To check the bulb, use a multimeter set to measure resistance and put one probe on the tip at the bottom and one on the metal side. A good bulb should have a very low resistance. A bad bulb will show an open, much like a blown fuse.

Assuming the nightlight is providing 120VAC directly to the bulb, take a look at Batteries Plus or here. While it will cost some more, you should be able to find a Batteries Plus store close to you and verify the size and fit is right. The second link has a video showing how to verify the size is correct with a pair of calipers.
 

Marcus2012

Joined Feb 22, 2015
402
Looks like it might be a BA9s bayonet cap type. Automotive bulb basically for older cars, not entirely sure though without the dimensions to hand. T4W might do the trick, if not then there are some with the BA9s cap and a narrower head.
 

Thread Starter

stormBytes

Joined Jan 26, 2010
41
I see the bayonet and automotive definitely makes sense. I can also make out the "4w" part, its the "60??" that's throwing me for a curve, especially since its an a/c nightlight. I'm guessing the voltage is stepped down from 120AC (resistors) and half-rectification el-cheapo style (see circuit pic) so my plan was to plug it into the mains, as is, and measure output voltage on the bare leads.
 

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Thread Starter

stormBytes

Joined Jan 26, 2010
41
One thing though make sure that it definitely says "60V4W" on the bulb and not "60V2.4W" The solder might be hiding it I can't make it out
Wow nice catch! I'm gonna have to see if i can get some of that solder off (wish i had a wick!)

And good call on the 2.4 --- I noticed it didn't seem to see 60V4W, theres some extra character there I couldn't quite make out.

All in all it seems like it would make more financial sense to just buy a new nightlight but.... i rarely make financial sense!

ps: anything specific I might look for in a soldering wick/braid?
 

Marcus2012

Joined Feb 22, 2015
402
Yeah I saw the 2.4W ones for sale and it clicked that it might be under there :). As for wick, generally the finer the wick the better the capillary action and some people swear by flux-impregnated wick and it is good but more expensive. You generally get what you pay for but I get by with cheap wick and apply flux as needed.
 

GopherT

Joined Nov 23, 2012
8,012
Wow nice catch! I'm gonna have to see if i can get some of that solder off (wish i had a wick!)

And good call on the 2.4 --- I noticed it didn't seem to see 60V4W, theres some extra character there I couldn't quite make out.

All in all it seems like it would make more financial sense to just buy a new nightlight but.... i rarely make financial sense!

ps: anything specific I might look for in a soldering wick/braid?
Looks like an Ne51 (neon mini bayonet) bulb.
 

Marcus2012

Joined Feb 22, 2015
402
Think it's a step down converter and the unwanted voltage is dropped across the capacitor and that 2.5M resistor is a bleeder resistor, but I am totally unsure though as I can't see the traces.
 

RichardO

Joined May 4, 2013
2,271
I like this theory because of the "60V" part of the number. If it is a neon bulb there will be a large value resistor (a few hundred kohms?) in series with it and no other components.
Oops. I should have looked at the pictures -- there are other components...
 

ian field

Joined Oct 27, 2012
6,539
I see what looks like 60 and 4W
That's what it looks like to me as well, and the small bayonet cap they used to use in dashboard clocks - not the bigger size used for side lights.

Not sure what uses 60V though, telecoms use mostly 48V and avionics is usually 28V.
 

Thread Starter

stormBytes

Joined Jan 26, 2010
41
Ordered some desoldering wick. Should be here by tomorrow. Then (hopefully) the mystery of the hidden lettering will be unravelled at last!
 

Marcus2012

Joined Feb 22, 2015
402
Doubt there's anything wrong with the PCB here and it just looks like a half wave rectifier like you said and a LDR/BJT switch, so it should work like..

Vmax = 120Vrms*1.414 = 169.68V

169.68/Pi = 54.01VDC equivalent

Just make sure that bulb is the right wattage :) Think it is 2.4W though, that's what my money's on :)
 
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