• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Very interesting CCS device

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
 
LTSpice drain curves

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

Attachments

  • 37462926-6485-4F5D-A3AF-FCBACA57D9F1.jpeg
    37462926-6485-4F5D-A3AF-FCBACA57D9F1.jpeg
    878.2 KB · Views: 433
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.)

-----------------------------

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.
 

Attachments

  • 211_datasheet-curves.jpg
    211_datasheet-curves.jpg
    329.2 KB · Views: 276
  • Sic_depl_Schade_triode.jpeg
    Sic_depl_Schade_triode.jpeg
    878.2 KB · Views: 275
Last edited: