DIY parts

[Ian Fritz]

Hi Terry --

Thanks for taking the time to answer the questions about the gate
capacitance. I think I have a better handle on what is going on now. 

I found a good web site for FET info -- belonging to the
Temic/Siliconix/Vishay people -- and they had the spec sheets I was
looking for. I was surprised to see they still have the 2N4859 in their
product list! Looking at the 2N4392 family I noticed that the 2N4391
seems like it might be an alternative to the 2N4859. It has only a bit
more resistance, and much less leakage and faster switching. 

They also have MOSFETs designed for high-speed and glitch-free
switching. If you're interested, check out the SD210DE. They also have
an interesting app note AN301. Their site is www.temic.com

As far as the output impedance of the 3130 ... have you ever thought of
not using an active integrator? I notice that the MOOG schematics I
found on the web have the cap just attached between a voltage reference
and the exponential current source. So the ramp starts at Vref and ramps
down to zero, where a comparitor fires the discharge circuit.  

Best regards,

  Ian