[personal] Transistor Substitution

Mike Hatch mike at brickfieldspark.org
Tue Jun 9 03:05:39 CDT 2009

> ----- Original Message ----- 
> From: "O. Sharp" <ohh at panix.com>
> To: <cctalk at classiccmp.org>
> Sent: Tuesday, June 09, 2009 6:25 AM
> Subject: [personal] Transistor Substitution

> 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.

Given the age of most DEC equipment there will be lots of transistors that 
will do the job. A quick Google with 2N3009 will come up with lots of info, 
Eg this site http://qrp.kd4ab.org/1997/971031/0071.html lists 2N3009 as an 
eqivalent to 2N2222 along with tons of others, any/most of which could be 
suitable. within reason a switching application would be less critical about 
spec changes than a precision analog application.
Look for the basic overall ratings to be similar, voltage, current, power 
dissipation and gain. Package type is not so important until you get to the 
larger power types, but watch for pinouts there are multiple variants of 
TO92, TO18 and the rest, you might have to move legs around for an 

You could go to the extent os setting up a small test rig & scope, get the 
signal conditions for a 2N3009 and then test some others.

> Is there a basic resource for determining modern equivalents for older 
> transistors and diodes? Can someone helpfully provide me with a clue here? 
> :)
> Thanks!
Best regards,
Mike Hatch

Web - www.soemtron.org
PDP-7 - www.soemtron.org/pdp7.html
Email - mike at soemtron.org

Looking for a PDP-7 (some hope!)  and an ASR33

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