MOTM

--- In motm@yahoogroups.com, Tentochi <tentochi2003@y...> wrote:
> I know some of this has been mentioned here before, but I forget 
all of the
> details and I can't find it in the archives.

More complete info can be had on the web from the datasheets for each 
of these devices.
> 
> Can someone please explain the differences between the BC549 and 
BC550 and also
> between the BC559 and BC560?

There is very little difference aside from the average gains and 
noise from a given number of tested devices.  The difference between 
the 549/550 and 559/560 is polarity- the former is NPN and the latter 
is PNP.  Transistors have quite wide tolerances.  It is not uncommon 
to find great variations in noise or current gain (hFe)when testing 
even a small number of devices.  In most circuits, this won't make 
any difference.  In fact, as long as the transistor has the correct 
polarity, you can usually substitute freely with only minor resistor 
value changes to make sure the device pulls enough current.  You may 
get more or less noise, but those differences would occur within a 
single transistor part number!  
> 
> Second, what are the differences between the A, B and C types?  
What if an A, B
> or C is NOT given after the part number?

See above.  These letter suffixs usually denote "improvement" in the 
average specs of a specific number of tested devices.  In some cases 
these specs can be radically different (BC108C's come to mind, with 
average hFe of 500!)
> 
> Are there any practical differences between these transistors when 
they come
> from different manufacturers?  In particular, Vishay and Fairchild?

Not anymore!  You can bet that your transistor was made by little 
girls in some Asian country while being physically and mentally 
abused, regardless of the name on the label.  There shouldn't be any 
variation in the average specs (see above) but it would be impossible 
for the average user to tell, much less care.
> 
> Thanks!
> Shemp

It's my job, sir and your'e welcome.  For a really good learning 
experience, build a small, single transistor, common emitter 
amplifier circuit on your protoboard.  Then drive it with a bit of 
white noise or a square wave and watch the output on a 'scope.  Heck, 
you could even listen to the difference through an amp and speaker.  
Leave all the components the same but change transistors.  Even 
within the same part numbers/suffixs/manufacturers, you'll be able to 
discern the differences.

Chub
ps- remember the word "transistor" is a contraction of two words - 
Transistional Resistor.  Dropping that bit of tid in conversation at 
cocktail parties will guarantee that you'll never be invited back!  
Perfect for avoiding dull events while you work on your music!
> 
> 
> 	
> 		
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