half germanium, half silicon diode!!!!

[Hal]

jk....kinda.  I just stripped some old cable tv box i had in my basement for some reason (probably from the late '70s) and almong the carbon comp resistors, I came upon beautiful diodes in glass cases, with blue lines, looking similar to the germaniums i see for sale on e-bay.  

so i pulled one off (carfully), tested with resistance to check conductivity one way (passed), and wired it with a 1k resistor in series and a 9v battery (reading 7v) I measured the voltage drop to be slightly higher than .45 volts.  

so....what is this ?

[brett]

Very useful!

Technically, I have no idea, though there are plenty of semiconductors besides Ge and Si.  Consult a periodic table??

[Hal]

yea...i know...but its not gunna be a gallium-aresenic diode in there :-D.  The thing is old and ghetto....so I dunno  I guess that is the only rational explanation...either that or my meter is messed up.

[Paul Perry (Frostwave)]

That is right on the money for a Schottky diode. Maybe it is from a foster/seely FM discriminator, were they next to a little RF coil thingy?

[Ge_Whiz]

Mr Frostwave could well be correct, but I have a number of germanium diodes in my collection with forward voltages as high as this. The exact value depends on a number of factors, including the dopants used in the germanium and the metal used for the point contact, not to mention the forward current flowing at the time of measurement. The usual quoted Vf values are at a current of 1 mA, and will increase markedly with increasing current.

[Hal]

That is right on the money for a Schottky diode. Maybe it is from a foster/seely FM discriminator, were they next to a little RF coil thingy?

there were _tons_ of coils in it, so yes, they were near one.  If it helps, there were 8 in total, 2 groups of 4, and they looked like they were in a bridge configuration, but i cant say for sure.  

time to put 'em to the test in a simple circuit :-D

[toneman]

U could use an ohmmeter and measure the forward&reverse
voltage drop.  If its .3V its ger, or schotky; if .6/.7 it's silicon.
If diode is in switching pwr supply, it's most definitely schotky.
Asfarasiknow, there is no ger/sil diode.  There *are* in fact,
ger/sil transistors, a fairly recent invention.  They are used
for very high frequency, low noise amplifiers.
Would they work for audio???  don't know.  never seen one,
only read about it in EDN or Electronics.
afn
tone

[zachary vex]

my schottky diodes measure less than .2 V forward drop.  germs tend around .3 V, silicons .5 to .6 V.  if you're seeing some funny forward voltage consider that it might be a zener which is designed to do something in the reverse direction.  i have one that measures .7 V forward right in front of me.

[Hal]

eh, i see the vf isnt as indicative as i thought it would be.

Do the colors mean anything?  one of the groups of 4 are blue, green, and the other one is green, yellow, red.  

and both measure vf's close to .4 when after i reduced the current to about 1ma.  

time to put 'em in a bazz fuss.  Or something like that.  But i've been lazy lol