J310 and U310 FETS By Steve Ratzlaff The J310 is a high-Idss
device, much higher than the general JFETs like your MPF102, 2N3819, 2N4416,
etc. It's also the defacto device (along with the same die in a metal can, the
U310 which is what I use) for almost all active whip-amps that use a JFET as the
input device. (The RF System's DX-1 Pro and the Amrad whip-amp use an RF power
VMOS FET with much higher input capacitance.)
The J308,309,310 are all in the same family, graded by Idss, with the 310 the highest minimum Idss; all 3 have about the same maximum Idss (Idss = "drain current with gate shorted to source"). I have determined in all my active whip-amp tests that best linearity occurs in the range of about 8-12mA drain current. Most seem to fall in the 9.5-11mA range. With most JFETs you can measure Idss, but this family will heat up and destroy itself if you let unrestrained drain current go for more than several seconds; the factory determines Idss for these with a pulse test. BASIC SPECIFICATIONS ARE: 25V max drain-gate voltage, 25 V max source-gate voltage 10mA max forward gate current 360mW max power dissipation. Gate-source cutoff voltage 2.0-6.5V Idss 24-60mA Gate-source forward voltage 1.0V max Common source forward transconductance (gain) 8000-18,000 micromhos Gate-source capacitance (what the input sees in an active whipamp circuit) 5pF max, 4.3pF typical Noise Figure at 105MHz, 1.5dB typical; 2.7dB typical at 450MHz Wide dynamic range--greater than 100dB Low-noise device, good for oscillators, mixers, amplifiers J310 PINOUT: Hold device with leads pointing toward you with flat face up--left to right--drain,source,gate (device is not symmetrical, i.e. source and drain cannot be interchanged) |