Infos about a weird vintage led (or something (?))

Discussion in 'General Electronics Chat' started by BulbChangeExpert, Mar 26, 2016.

  1. BulbChangeExpert

    Thread Starter New Member

    Mar 26, 2016
    i had this unidentified light bulb since several:rolleyes: years, it has a diameter of 5mm(ish), i really don't know anything about it (if it's a led or whatever, how to power it...) i took it from a TV of the '60-'70 (likely), they where two, at the times i broke one of em to see what's inside and that whiteish stuff is some sort of silicone semiliquid gel, the envelope is glass, there's that weird little bar into the gel that looks like a semiconductor (?)

    (i powerd it... with a dmm in diode test nothing happens, i gradually powered it trought a resistor and nothing more than 30uA flows in both directions even if i apply 24V directlyo_O DSCF5428.JPG )
  2. sootydog

    New Member

    Jul 23, 2011
    Looks like an old photodiode to me, something like the dg2 on this page with the paint removed.
    DickCappels likes this.
  3. BulbChangeExpert

    Thread Starter New Member

    Mar 26, 2016
    thanks... you are probably right, this explains both the 30uA thing, the shape and the fact that it was placed in a visible place, i have to investigate the light response, however i didn't remove any paint
  4. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    Its a photo diode, for infrared remote control signals.
    Tonyr1084 likes this.
  5. Tonyr1084

    Well-Known Member

    Sep 24, 2015
    Quick suggestion: If it's an infra-red emitter use your cell phone camera to detect the light. In fact, using a cell phone camera is how I determine whether a TV IR Remote is functioning or not. True, you can't distinguish cycles or pulses, but you WILL get a visual representation on the cell phone screen if the LED is lighting up or not.

    This is a case of using the cell phone as a diagnostic tool.

    IF, as DodgyDave suggests "it's an IR receiver" then using a scope and a TV remote should trigger it. You WILL have to design a circuit to supply a power source and the IR Receiver to switch it on - either way you'll know for sure what it is. Judging from the picture, I think DodgyDave is probably right.
  6. BulbChangeExpert

    Thread Starter New Member

    Mar 26, 2016
    mhhh.. they where two, if i remember well they where the same (looking at em).... maybe one is used for light adaptation and the other... well... maybe as IR receiver... but the TV was from an era that remotes where not experimented yet (maybe)

    it was INTO the TV, i hadn't any remote (the tv was already broken (of course:D))
    also i know that IR receivers are extremely sensitive devices that work no good with leads so long on the IR diode
    but i have plenty of IR LEDs so exciting it won't be so hard

    i'll update you all this evening (italy time zone:rolleyes:)
  7. Tonyr1084

    Well-Known Member

    Sep 24, 2015
  8. GopherT

    AAC Fanatic!

    Nov 23, 2012
    With only micro amps of current low, It could be a phototransistor (no external base pin access) or photodiode for an automatic gain control (if there was access to some lamp or tube light source).

    On the other hand, it could have been an IR emitter if you tested it without current limiting and fried it to make a open circuit.
    blocco a spirale likes this.
  9. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
    It's surprising just how many devices can be made to operate as IR emitters:).
  10. InspectorGadget

    Active Member

    Nov 5, 2010
    I really doubt it's a photoelectric device of any kind.

    1. You wouldn't put a milky gel into a photoelectric device because that will just decrease the light falling on it.

    2. Why would there be TWO of them if it were a remote-control photo receptor or an ambient light compensator?

    3. A big bar of something between two electrodes doesn't translate into any photoelectric device I've ever seen.

    I think it's most likely a thermistor of some kind, like a "rod" thermistor, and the gel is a heat-conductive grease.

    Thermistor_5df879e0ebb2d0329bf3e594e0a0766c2118cfef.jpg thermistor_3.jpg Thermistor_302254_gallery_53f713689ab37_gif_fa_rszd.jpg
  11. BulbChangeExpert

    Thread Starter New Member

    Mar 26, 2016
    actually i don't remember if i powered it properly at the times i scavanged it:D but i've read that the BPW34 operates up to 60V

    like anything that is hot?:)

    no... it was placed at a (semi)visible spot on the TV;)... infact

    it's a very nice photodiode:p, a visible spectrum type
    right now i don't know how it's possible that it conducts in both directions, but i somehow obtained its response to different light colors
    they are....
    -110 uA -wood's black light
    -230 uA -royal blue
    -1300 uA -green
    -880 uA -red
    -1500 uA -cool white
    i loaded it with a 9V batt and a 1k resistor, i used some 5mm clear leds for all the tests exept the black light that is a CFL 26W (face to face the led at 1cm, black light at 10cm)
    of course there's the fact that different led colors emit different amount of light, i didn't tested with IR because it's obviously a visible spectrum one, i also suppose it's not a phototransistor

    likely it was used for CRT luminosity vs ambient compensation (quite common)