please help me identify this device.

[shadowlord]

hopefully someone here yould help me out with this little bugger...

i've found an old magnetic driven clock at a garage sale.
since i'm interested in old things i tried to get it working again.

the unit shown above lies somewhere between the coils but i have no clue what it is?
a transistor maybe.
i could try change it with a new part as soon as i know what it is.

 

[sovs]

pnp germanium transistor. made by GE, an OC75A as you can see yourself

there is a circuit to test it here...

http://www.buildyourownclone.com/board/viewtopic.php?p=26503&sid=ea8be3db8383c5bc1c5765155eb5be78

easy thing to buy new

 

[Fourfifth]

Looks like a Germanium based transistor. Would need to see a schematic, or better overall view of where its in use.

FF

 

[Fourfifth]

Looks like someone beat me too it

 

[shadowlord]

thanks for the replies.

do i need the circiut in the link to test it or could i use this thingie on my dmm in some way.
( maybe this shows my electronic noobnes)

 

[Mohonri]

Yes, your DMM will measure the hfe of that transistor. Just make sure you put the right legs in the right holes.

 

[sovs]

the red dot means its PNP, so you want the left set of holes..

the red dot also identifies the collector, so that goes into the C hole.
the centre wire is always the base, so thats B.
whats left goes into E..

no idea why there are two E holes

 

[Mohonri]

I don't think the base is always the middle pin--I've seen plenty where the base is one of the side pins. It's probably best to find a datasheet somewhere. Of course, I doubt the DMM will wreck that BJT by testing it, but I could be wrong.

 

[cpemma]

the red dot means its PNP

It is a PNP, but I always thought the red spot had another significance;

during the 1960s...although full spec transistors were hideously expensive you could buy a red spot AF transistor or white spot RF one for a few shillings or so - still not particularly cheap at the equivalent of several pounds in today's bottle top money! These devices were manufacturers' seconds, usually on grounds of noise or lowish gain. However they usually worked satisfactorily in constructional projects.

There is a datasheet for the OC75, middle pin is base for this one.

 

[shadowlord]

thanks for all that info so far.

i found a bit time this weekend to disassemble the clock again.

i put the transistor in my dmm and messured a hfe of 280.
the datasheet linked above says hfe 60...130 for a oc75, i assume the transistor is deffective...is this right?
i installed a battery today and it instantly got very hot like it was shotened out. does this speak for my deffective transistor theory?

if so, i will try to buy an replacement tomorrow.

iv'e drawn a simple circuit digram in paint if anyone is interrested how the clock works.

 

[RacerX27]

no idea why there are two E holes

EBC or ECB you can plug in a component without crossing legs. 4 different plug in options with EBCE sockets, without crossing legs.

 

[RacerX27]

The part is most likely good, higher hfe wouldn't hurt in most cases. The fact that is has gain and is reading most likely means its good.

You can use the ohms meter to measure a diode junction from B+ to C- and B- to E+. E to C will be open C+ and E-. And something like a diode junction E- to C+. For a PNP. Backward for a NPN.

I use a Huntron Tracker 2000 to see the junctions, I can tell if it has any failed junctions or if any junctions are breaking down. The hfe test is almost as good to see the quality of the entire part, fact that it has a hfe means the 3 legs are working together.