11 Jun
2009
11 Jun
'09
5:42 p.m.
Thanks for all the replies so far. While what I've seen so far is
definitely helpful, particularly regarding the 2N3009, I'd like to take a
step back and generalize the question a bit.
Let's say you have a system where something dies, and you trace it down to
a particular transistor. You do a search for the part number, and find out
that particular part is no longer manufactured and/or available. You find
a datasheet, though,, and between that and the circuit you get a pretty
reasonable idea what the transistor's specifications ought to be like. So
far, so good.
The problem I run into at this point is how to go about finding a modern
substitute. Some of you are up on your specs for modern transisitors to
the point where you can just casually say, "Oh, well, I know a part that
ought to be able to handle that," and you're home free. It's admirable,
That's the easy case :-). You tend to remember the common transistors
(2N2222, 2N3904, 2N3906, 2N2219, 2N2907) and look up the specs of those
first (if you can't remember them).
Waht I used to do (I'll explain the 'used' in a minute) was based on the
obvious fact that the substitute was only useful if I could get it. So
I'd gra the catalogues for 2 or 3 suppliers and look down the list of
transistors (normally only 2 or 3 pages) which included brief specs to
see which would be suitable. If I was in doubt, I'd look up more detailed
data on the couple of 'possible' devices.
Why 'used to'? Well, you can't get paper catalouges from some suppliers
any more. They expect you to use their web page. And I find it impossible
to find transistors that way. The web pages were not set up by engineers,
or even people remotely clueful in electronics. And you get some sillies
(like some transistors being listed witha maximum collector current of
1A others 1000mA. Of course a search will find one and not the other...)
I've kept paper catalouges from about 10 years ago, I look in those for
suitable candidates and hope they're still available...
-tony