9 Jun
2009
9 Jun
'09
9:43 a.m.
O. Sharp schrieb:
Okay: I admit it, I am sometimes pig-ignorant about
basic hardware
questions. :/
I have a couple of DEC machines which I need to replace a few components
on, and also stock up spares of others. With the transistors and diodes,
however, I often can't find a direct replacement - and don't know how to
figure out what a modern substitute is.
For a 2N3009, for example, I can find basic information and a datasheet
online easily enough - but as for choosing a functional, available
substitute for it, I'm honestly not even sure where to begin.
Is there a basic resource for determining modern equivalents for older
transistors and diodes? Can someone helpfully provide me with a clue
here? :)
There exist books which provide cross references replacement types for
obsolete components. Often manufacturers also provide lists in the Web
which recommend their own modern components for such old transistors.
Google is your friend there.
The point, however, is that one should carefully look at the circuit
itself to find out what the transistor is actually used for.
Take a basic amplifier, for instance (two resistors at the base, and
one each at the collector and emitter, resp., AC-coupled). This circuit
is built around certain transistor characteristics; IIRC, the AoE book
describes the formulas. Unless you also replace the passive components
around it, you should have a replacement with the same hfe21, Ube, Ic, Ib,
and maybe even fT, etc.
But often, this whole work is not required at all. The 2N3009 is not a "high speed
switching NPN" with respect to modern devices - it may have been 30 years ago,
and the other parameters do not really suggest it is something really uncommon.
For some HF transistors, there may be a problem (cf. amplifiers!), but unlikely here.
In digital DEC machines, such a beast is possibly just used for driving
display bulbs, in the power supply, or converting voltage levels -
I don't know the circuit you refer to.
In such a case, I have no problems to take some modern standard NPN with
almost the same characteristics (Ic, Uce, P, hfe) which I find in my
semiconductor box.
--
Holger