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LTSpice triode model

Discussion in 'Electronic Design' started by Andrew Holme, Nov 26, 2008.

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  1. Andrew Holme

    Andrew Holme Guest

    I found these triode models:

    http://www.duncanamps.com/spice/valves/dmtriodep.inc

    The LTSpice .asc file below shows anode current when Vgc < -80V. Do valves
    do this, or is it a bug in the model? What's the fix?

    Version 4
    SHEET 1 2020 680
    WIRE 928 176 832 176
    WIRE 928 192 928 176
    WIRE 832 288 832 176
    WIRE 928 288 928 272
    WIRE 928 336 880 336
    WIRE 928 368 928 336
    WIRE 864 464 864 384
    WIRE 928 464 928 448
    FLAG 928 288 0
    FLAG 928 464 0
    FLAG 864 464 0
    SYMBOL voltage 928 176 R0
    WINDOW 123 0 0 Left 0
    WINDOW 39 0 0 Left 0
    SYMATTR InstName Va
    SYMATTR Value 150
    SYMBOL Misc\\triode 832 336 M0
    SYMATTR InstName U1
    SYMATTR Value NH12AU7
    SYMATTR SpiceModel NH12AU7
    SYMBOL voltage 928 352 R0
    WINDOW 123 0 0 Left 0
    WINDOW 39 0 0 Left 0
    SYMATTR InstName Vgc
    SYMATTR Value ""
    TEXT 1040 288 Left 0 !.include dmtriodep.inc
    TEXT 1040 368 Left 0 !.dc Vgc -150 0
     
  2. Fred

    Fred Guest


    Basically there are two kinds of triode models, the Leach and the
    Koren. I favor the Koren models. I have found them to be reasonably
    accurate if you stay within normal operating parameters. Get too far
    away from that and the models get quirky.

    Best regards,

    Fred
     
  3. Tim Williams

    Tim Williams Guest

    I don't know (or care ;-) ) much about SPICE, but I know plenty about 12AU7.
    If plate voltage is over 1kV or so, I might expect to see some current
    at -80Vg. At any plate voltage, there will be some leakage, which should be
    much less than a miliampere, especially at -80Vg.

    Tim
     
  4. Andrew Holme

    Andrew Holme Guest

    The above model is very wrong at Vg < -80V.

    I've just found a better one on the same website:

    http://www.duncanamps.com/spicevalvest.html#12AU7A
     
  5. Andrew Holme

    Andrew Holme Guest

    Better in one way, worse in another :(

    This manages to suck 22.8mA through a 68K anode load resistor from a 150V
    supply, giving an anode voltage of -1.4KV.
     
  6. Andrew Holme

    Andrew Holme Guest

    I'm now trying the Norman Koren models, which seem to take anode voltage
    into account and do sensible things at both extremes of grid voltage.
     
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