[sdiy] moog transistor matching circuit question

[Ian Fritz]

On 1/10/2016 7:58 AM, Simon Brouwer wrote:
> Hi Matt,
> It is basically the same method as I described, but using the internal
> current source of the multimeter.

Also the method described by Jim Patchell 10 yrs ago or so.  :-)

My method is the differential version of this measurement.  It's main 
advantage is that it's easy to get the devices at the same temperature 
-- just mount them to each other, block any drafts, and wait until the 
measurement stops drifting.

>>
>> Thanks Simon. Consensus of everyone I asked is that it's the resistor
>> isn't needed, so then the lack of one in the PNP tester isn't a
>> "flaw". I like your idea of it being for current measurement, that
>> seems very plausible. I'm gonna go with that explanation =)

More likely, it seems to me, is that it is just a current limiting 
resistor for protection in the event that the current source should 
fail. (eg, opamp goes to - rail)  A kind of safety valve.

Ian