stupid questions...

[Ingo Debus]

Roel Das wrote:
> 
> Please forgive me if this is a stupid question, but
> how can you determine which are the E,C and B of a
> transistor, without any datasheet? 

You can do this with a simple ohmmeter. B-C and B-E behave like diodes.
There's practical infinite resistance between E and C when B is
unconnected (for silicon trannies). This way you can find out which is B
and if you got a npn or a pnp. 

To find out which is E and which is C, connect these to the ohmmeter,
and for a npn, touch the tranny lead connected to the plus lead of the
ohmmeter and the base with a wet finger. Repeat that test with the
ohmmeter's leads exchanged, but still touching the plus lead and the
base with your finger. If the ohmmeter shows way lower resistance, the
ohmmeter's plus lead is connected to C and its minus lead is connected
to E. For pnp it's all the other way around.
Careful: analog multimeters in ohmmeter mode often have the black lead
as plus and the red lead as minus (unlike in voltmeter mode).

This works good for silicon trannies, but not for germanium ones.


> And another stupid question, how can you see the
> difference between logarithmic and linear pots?

Turn it into center position and measure the resistance between wiper
and one end and between wiper and the other end. If both resistances are
about the same, it's linear. For log pots, there's a big difference in
resistance.

Ingo