--- In LTspice@..., Bill Lewis <wrljet@y...> wrote:
Please post any replies to this question to the list.
I'm interested in vacuum tube modeling.
... and the obvious question: How do I relate the previous info
with
the symbol.
Hello Bill,
you will find the symbol in the "misc" directory.
A short description follows:
1. Load the triode symbol into your schematic.
2. Replace the value 'triode' with the model name used in the model
file. In this case it is '12AX7A'.
3. Put the model text into a file and store it in your working
directory. That is the directory where your schematic is.
4. Add the line .INCLUDE modelfilename in your schematic.
That's it. This procedure will work for any kind of part and you can
put as many models you want into one file.
It is important for any kind of symbol and model that the pin order
is matching. Let's take a look to the triode symbol. The provided
symbol has the pin order P(1), G(2), K(3). The model text
uses .SUBCKT 12AX7A P G K . This means that P is pin-1 G is pin-
2 and K is pin-3. We have luck, the pin order is the same. If it is
different, then we could either change the order in the model text or
in the symbol.
I have the ready to run example files attached.
By the way, the model isn't good at low Vpk voltages. Take a look to
the Ip(Vgk, Vpk) plot to see what I mean.
Best Regards
Helmut
The model file: triode_12ax7a.sub
---------------------------------
* 12AX7A Triode PSpice Model 8/96, Rev. 1.0 (fp)
*
* -------------------------------------------------------------------
* This model is provided "as is", with no warranty of any kind,
* either expressed or implied, about the suitability or fitness
* of this model for any particular purpose. Use of this model
* shall be entirely at the user's own risk.
*
* For a discussion about vacuum tube modeling please refer to:
* W. Marshall Leach, jr: "SPICE Models for Vacuum-Tube Amplifiers";
* J. Audio Eng. Soc., Vol 43, No 3, March 1995.
* -------------------------------------------------------------------
*
* This model is valid for the following tubes:
* 12AX7A/ECC83, 7025, 6EU7, 6681, 6AV6, 12DW7/7247 (Unit #1);
* at the following conditions:
* Plate voltage : 25..400V
* Grid voltage : 0..-3.5V
* Cathode current: 0..8mA
*
*
* Connections: Plate
* | Grid
* | | Cathode
* | | |
.SUBCKT 12AX7A P G K
E1 2 0 VALUE={45+V(P,K)+95.43*V(G,K)}
R1 2 0 1.0K
Gp P K VALUE={1.147E-6*(PWR(V(2),1.5)+PWRS(V(2),1.5))/2}
Cgk G K 1.6P
Cgp G P 1.7P
Cpk P K 0.46P
.ENDS 12AX7A.SUBCKT 12AX7A P G K
The circuit file: triode_test.asc
---------------------------------
Version 4
SHEET 1 1104 692
WIRE 336 384 336 496
WIRE 368 288 368 224
WIRE 368 224 512 224
WIRE 512 336 512 224
WIRE 512 416 512 496
WIRE 512 496 336 496
WIRE 336 496 176 496
WIRE 176 496 176 448
WIRE 176 368 176 336
WIRE 176 336 320 336
WIRE 176 528 176 496
FLAG 176 528 0
SYMBOL F:\PROGRAMME\LTC\SWCADIII\lib\sym\Misc\triode 368 336 R0
SYMATTR InstName U1
SYMATTR Value 12AX7A
SYMBOL F:\PROGRAMME\LTC\SWCADIII\lib\sym\voltage 176 352 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 0
SYMBOL F:\PROGRAMME\LTC\SWCADIII\lib\sym\voltage 512 320 R0
SYMATTR InstName V2
SYMATTR Value 200V
TEXT 142 136 Left 0 !;dc V2 0 200 0.1 V1 -5 20 5
TEXT 136 176 Left 0 !.INCLUDE triode_12ax7a.sub
TEXT 592 136 Left 0 ;.dc V2 0 200 0.1 V1 -5 20 5 Ip(Vpk, Vgk)
TEXT 144 96 Left 0 !.dc V1 -5 20 0.1
TEXT 592 96 Left 0 ;.dc V1 -5 20 0.1 Ip(Vgk)
