[sdiy] transistor matching circuit

[Scott Bernardi]

I think building a curve tracer is kind of cool, however I don't think 
it would be adequate for Vbe matching. When I match transistors,  I'm 
looking to get their Vbe's matched within a millivolt at two different 
currents.  So I'm looking at the third and fourth decimal places on my 
DVM out of 600 or so millivolts - i.e., comparing numbers like 0.6235 
and 0.6241, a  0.2% difference. Can you get that kind of resolution on a 
scope?
My little circuit here 
http://home.comcast.net/~sbernardi/elec/og2/transistor_tester.html can 
test npn or pnp transistors and has a switch for changing the current 
from 5uA to 500uA.  Mostly I end up measuring 2N3906's because npns are 
fairly easy to obtain in matched arrays. It uses a mini-DIP for the 
transistor socket so I just flip it to 5uA, grab a transistor with a 
pair of pliers (not your fingers) and plug it in, wait 30 seconds, 
record the BE voltage, flip the switch to 500uA, wait 20 seconds,  and 
record the second Vbe.  I have a piece of cardboard with a strip of 
double sided tape that I write the voltages on then stick the transistor 
next to the recording. In less than and hour I have 40 or so measured 
transistors and there are usually enough matched within a millivolt 
pairs within that to last me months.
Just make sure you do it in a draft free location and move slowly when 
you reach over to flip the current switch.

J. Larry Hendry wrote:

>Hey hey. :-)  I built one of these in 1975 just for testing transistors.  It
>still works fine. I never considered it for matching.  Of course, without a
>storage scope, I guess it is still not too good a matching tool.  Humm.... I
>wonder if the digital camera would come in handy here?
>Larry H
>
>
>-----Original Message-----
>From: owner-synth-diy at dropmix.xs4all.nl
>[mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of Tom McClintock
>Sent: Tuesday, December 14, 2004 6:57 PM
>To: SDIY
>Subject: Re: [sdiy] transistor matching circuit
>
>
>DIY curve tracer:
>
>http://www.ionpool.net/arcade/tech/octopus.pdf
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>tm
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