Static Induction Transistors = Triode-Like Behavior?

[polaris26]

I just came across this article from an audio zine and thought it might be of interest to someone here with regard to making tube-like distortions - it talks about 'Static Induction Transistors' like the 2SK82 and how they exhibit triode-like transfer characteristics.  Perhaps this could be used to advantage in creating more tube-like distortion effects?

http://www.diyaudio.com/forums/diyaudio-com-articles/200460-l-amp-simple-sit-amp-part-1-a.html

cheers,
Dave

[CynicalMan]

$22 ea.
http://www.circuitdiy.com/product/2sk82-sony-n-ch-vfet-for-ta-n88-class-d-amp

[PRR]

> 2SK82

2SK82's happy-zone is several AMPEREs. Power-amp (maybe), not low-level signal procesing.

And they are only grossly "triode-like". The fine detail is different from vacuum triodes.

Interesting because you can slap together a 2-Watt power amp from a 2SK82 and a light-bulb (and a laboratory-size power supply).

[amptramp]

In spite of the curve tracer diagrams, I am not ready to endorse SIT's as I have not seen anything about the device capacitances.  Whereas a triode tube may have interelectode capacitances on the order of a few pF that remain constant over the range of operating voltages, semiconductor devices have high capacitances that change dramatically with voltage.  Thw capacitance from gate to drain of a power MOSFET may be on the order of 1500 pF and decreases with increasing drain voltage.  Small signal MOSFET's generally have capacitances on the order of tens of pF and reverse transfer capacitances of several pF, similar to a triode but much higher than a pentode.  See the 2N7000 datasheet:

http://www.datasheetcatalog.org/datasheet/fairchild/2N7000.pdf

Note the reverse transfer capacitance of Figure 9 in the spec sheet.  JFET's  and BJT's exhibit the same sort of variation in capacitacnce due to the dielectric constant of the semiconductor and the movement of charge layers.  Tube capacitances have almost no variation with operating point, so capacitive effects are linear.  Nonlinear capacitance gives you a nolinear transfer function that varies with frequency.

All semiconductor devices have nonlinear capacitances with the reverse transfer capacitance being most important (unless you are willing to make every stage cascode).  Note that some people like single-ended triode amplifiers in spite of their noticeable distortion.  I have listened to them - they do not sound like the original music, but the distortion is pleasant and not at all harsh.  SIT amplifiers may be in a similar category, but I prefer to design amplifiers to minimize distortion.