Making a Xmas tree light bulb tester

[W. eWatson]

I understand their our tree light testers that allow one to slip a bulb
into a hole, and an led will tell you if its defective. I found one
something like that on Amazon, but it's pretty pricey. They may be
called proximity testers. Can one be made easily?

 

[Jasen Betts]

I understand their our tree light testers that allow one to slip a bulb
into a hole, and an led will tell you if its defective. I found one
something like that on Amazon, but it's pretty pricey. They may be
called proximity testers. Can one be made easily?

audio amplifier with capacitive probes,
when the string powered there will be an increased
electic field level in the vacitinity of an open-circuit failed bulb.
and reduced field near the working bulbs.