UFOs or unidentified funky objects

[Jason]

Is there any part of the forum where people can help you identify electronic components? I found a part in my electronics collection and I have no clue as to what it is. Actually I  know it is a diode, perhaps a zener,  but not any type I have ever seen before. It has absolutely no markings so I can't check part numbers. Anyway when I put 5 volts through it forward biased, it current limited to 2.6v @ 100mA, the centre of the diode lit up like an LED which I didn't expect. So then I removed the current imit and it took all 2 amps my supply could give and died a smokey death after 3 seconds like you would also expect from an LED. So then i got another one and it seems to work quite well on low voltage low amps, actually a little too well.  I could power the diode at 1.6 volts and the light inside the diode remained visiably lit when drawing 100uA MICRO amps!  I enjoyed playing with it but what is it? I tried to check if it was a zener by using it in reverse biased but it wouldn't break down up to 30 volts that my supply could provide.  I only have these 3 left after burning the other one so i don't want to kill them all.

As seen from 2.6v @ 100ma forward biased

[SeanB]

Probably ordinary general purpose silicon diodes. Most likely a 1N4148 or ISS2 ( generic version of the 4148 often used in Japan) which is a 10ma 75V diode. They do glow red if overdriven ( it is a LED anyway, just most is in the IR spectrum) and you can get them quite bright before they burn out. As I have a lot of silicon diodes ( bought 2 boxes of 10 000 12V and 24V zeners on auction one day for under $2) I have cooked a fair number both by accident and deliberately, you can often get them to stretch out just before dying to make little glass blobs.

[Jason]

Thanks Sean. That would make a lot of sense. Is there any way to narrow down what voltage and current they are rated for, or is it just a simple matter of trial and error? I have a bid on eBay for 50 military spec 3.9v 500mw Zener for a buck. Ebay can be a gold mine sometimes.

[SeanB]

Try using a higher reverse voltage, if they break down at between 100 and 150V then they are 1N4148's.

I really should open an eBay account, but that will be a total time and money sink, especially as postage to ZA is so expensive.  If I really want something then I might do so, but just having it a click and money gone and a month and a half away delivery kind of sucks big time.

[Jason]

I am getting 500 quad op amps next week for €9 including shipping  from the UK to here in Ireland. I might keep 100 or so and sell the rest so I can buy a nice load of resistors and capacitors, since I don't have a good selection. Perhaps you could do the same, sell your surplus stock to local, budding electronics enthusiasts so that you have extra money to buy items you have less of or would like to have. I mean you could buy metrology grade passive components and make your own DMM check out of interest from the proceeds. I would like to do that when I have a semi-basic lab setup.