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Very interesting CCS device

woody

Member
Paid Member
2002-01-15 12:57 am
Tyrone Ga. U.S.A.
UnitedSIS has a couple of high voltage high power jfets with interesting curves. If you look at this device you see that there are no curves for more than -8v on the gate so I tested one with about -9v on the gate. Using a 110 ohm source resistor to generate the - voltage at the gate I got 9.08 v across this resistor when using 36 vdc on the drain. When I went up to 300V on the drain the voltage across the 110 ohm resistor only went to 9.26V Ok that's not a perfect CCS but it's darn good and it's a cheap $6.09 190w part. https://www.mouser.com/datasheet/2/827/DS_UJ3N065080K3S-1530401.pdf
 

savu

Member
2007-02-07 5:27 pm
Bern
LTSpice drain curves

Hi there, I’ve used the spice model they offer and tried this... looks very triode like... very
 

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looks very triode like... very

Looks like a 211 curve wise. Except 100X the current. Can make a direct drive SET with an inductor.

that’s because of R2 I guess, since a naked JFET is pentode like.

Yeah, I think so. "Shunt Schade" changing pentodes into triodes. Could also put a TV damper diode under the Source terminal, to get 3/2 power curves instead of 4/2 power curves.
 
UnitedSIS has a couple of high voltage high power jfets with interesting curves. If you look at this device you see that there are no curves for more than -8v on the gate so I tested one with about -9v on the gate. Using a 110 ohm source resistor to generate the - voltage at the gate I got 9.08 v across this resistor when using 36 vdc on the drain. When I went up to 300V on the drain the voltage across the 110 ohm resistor only went to 9.26V Ok that's not a perfect CCS but it's darn good and it's a cheap $6.09 190w part. https://www.mouser.com/datasheet/2/827/DS_UJ3N065080K3S-1530401.pdf

nice but too much capacitances.
st has mosfets with <1pf crss
 
can you give more details on this toppic pleae?

211 tube plate curves below, look similar.

The SIC with 20 Amp curves could be used in a SET like mode (using the R2 'shunt Schade" scheme to get "triode" curves) directly without an OT for impedance transforming. Just would need a high current gapped inductor to a LV "B+" instead of the usual OT primary. A suitable Mosfet will work for Schade "triode" the same way, would be cheaper probably. Could duplicate a 211 SET for 1/100 the price. Will be low 2nd harmonic with such uniformly spaced curves.

If some parallel (to get near a 20 Amp rating!) TV damper tubes were placed in series with the Source terminal, then the gm curves would more closely resemble the 3/2 power law shape of a tube instead of the 4/2 power law of a Mosfet/Fet. (Most -power- tubes are closer to square law, ie. 4/2 power anyway, so not really necessary.)

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nice but too much capacitances.
st has mosfets with <1pf crss

Yes, this part is more suitable for direct speaker drive currents at 100X the current of a typical tube, where its high C would be expected. For tube replacement or tube CCS duty, a smaller SIC FET model is needed, with way less capacitance, especially lower crss for CCS duty.
 

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