I've over 30 of these little beasts. Absolutely nothing marked on them. They are, by testing them , photo-voltaic diodes and based on the length of time sice I retired - 25 to 30 years old. Any suggestions for a maker or type number ?

 

They are, by testing them , photo-voltaic diodes

Presumably you didn't see any light emission from them during testing. LEDs can also exhibit a photo-voltaic effect. Is it possible that your diodes are infra-red LEDs? Or did your tests eliminate that possibility?

 

Hello,

As @Alec_t said, it could be a led.
This page shows the history of leds, witha picture that looks like yours:
https://www.luxalight.eu/en/led-history

Bertus

 

How did you test it?
It looks like the case Thorn used to use.
http://www.lamptech.co.uk/Spec Sheets/LED Thorn TO-18 Yellow.htm
.

 

Absolutely nothing marked on them.

Most don't. That's a high reliability package. If you have phototransistors, you can use them to see if the components emit light in the range that they're sensitive to. You might also be able to use your smartphone if they're UV.

 

To test as a photo-emitter, use a 1k-3kΩ resistor in series with the device and a 9V battery. ( I would assume that the tab on the device case goes to negative polarity.) If there is no visible output, use a smart phone in camera mode and look for output.

 

If there is no visible output, use a smart phone in camera mode and look for output.

That is old-fashioned advice that works sometimes.
More and more cameras have near-IR filters so your advice would fail the OP. The iPhone main camera definitely has a filter to remove IR - the newer Samsung phones also have nearIR filters. The rear-facing camera on some iPhones don't have IR filters but you'd have to test. Also, it depends on the wavelength. Some cameras don't pick up wavelengths above 900nm so your advice relies on hope that the LED is the 830-840nm range.

 

Thanks all..I saw this a bit late to check tonight but I'll re-test tomorrow and look for signs of light (inc UV) output and report back..