[sdiy] Saw core JFET mystery

[Dave Manley]

David G. Dixon wrote:
> Hey Team (especially Ian Fritz):
>
> ...
>
> So, why can this RC be so much smaller than everyone else uses?  Is the
> PN4391 that much different than the 2N4391?  They should be virtually the
> same.  My integrator cap is only 1nF, so it will drain pretty fast, but
> still...?
David, you're in a university environment right?  Go over to your EE 
friends and see if they have access to a transistor curve tracer.  If so 
measure a bunch of each type and determine the device variation.  
Perhaps you'll find the drain to source resistance is lower for the new 
devices.  If a curve tracer isn't available you can do the same with a 
couple of power supplies and some patience.

-Dave

P.S. Take a look at Motorola AN211A for a good basic discussion about 
FETs.  Maybe it will give you some other ideas.