Replacing a blown bulb in a Mutron LDR, what should I use?

[washburnkc70v]

I've got one of these and thought it might be cool to use it in a Neutron build.  As far as I can tell the photoresistors are good but the bulb is blown.  Notice in the photo that these come apart easily, so my thinking is that I could possibly drill out the old bulb and put a new one in.  I'm just not sure what the best replacement would be.

[washburnkc70v]

 

[mdh]

It's probably an LED, but if you can get it out somewhat non-destructively, you can tell for sure. Maybe you could chip away at the potting compound (the bubble near the top of your photo) and pry the thing out. Of course, if you're going to use this in a Neutron, you'll want to use an LED anyway. It's hard for me to tell what size from the photo, and I don't know what color would be best, so if I were you, I'd just experiment a little bit.

If you have a breadboard it should be pretty easy to make a little circuit that varies the current to the LED (could be as simple as a battery in series with a current limiting resistor and the LED; just change the resistor to change the current). Then stick the LED and LDR in the little sleeve, turn out the lights if necessary, and measure the resistance of the LDR. Look for an LED which gets you close to the full range of resistance from the LDR (you can get this by covering the LDR with your thumb to get the dark reading (high R), then holding it up to a light to get the fully illuminated reading (low R). You might want to check both sets of leads to make sure that both LDRs in the package track reasonably well with each other, but honestly I don't know how important this is (even though I've built a Neutron myself!).

If you don't have a breadboard, you could build the test circuit on perf with sockets.

Good luck.