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News:

Spectrum Software has released Micro-Cap 11, the eleventh generation of our SPICE circuit simulator.

For users of previous Micro-Cap versions, check out the new features available in the latest version. For those of you who are new to Micro-Cap, take our features tour to see what Micro-Cap has to offer.

 

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New Duncan Munro Vacuum Tube Models

 

New vacuum tube models created by Duncan Munro have recently been ported to the Micro-Cap 6 parts library. There are nineteen triodes and eight pentodes. Some have heaters and some don't. The breakdown looks like this:

Triodes No Heater
2A3
3CX300
SV6AS7
6BM8
6DJ8
6N1P
6SN7GTB
12AT7
12AU7
12AX7
76
SV5723
SV57210
5751

Triodes With Heater
6SN7GTB_H
12AT7_H
12AU7_H
12AX7_H
300B

Pentodes No Heater
6BQ5
6CA7
6KG6
6L6
6V6
SV83
6146
EF86

The models and several demonstration circuits have been ported to MC6 and will soon be a part of the MC6 package.

As an example consider the circuit below.
12AX7 Tube Circuit
This circuit was used to sweep the plate voltage to generate the plate characteristics of the 12AX7 tube. The figure below is a plot of the static plate characteristics of the 12AX7 tube as calculated by MC6.

12AX7 Characteristics
Here are the actual plate characteristics from an old GE tube book (circa 1958). The match is very close and a tribute to Duncan's modeling work.
12AX7 GE Characteristics
The figure below shows the tube configured as a linear amplifier.
12AX7 GE Characteristics
Here is the transient response to a sinusoidal excitation.

12AX7 Transient
Here is the AC gain plot of the same circuit.

12AX7 AC
Note that the gain at 1KHz matches the gain as measured in transient analysis.

If you have an interest in the circuits, models, or other esoterica of vacuum tubes, you should see Duncan's site at http://www.duncanamps.simplenet.com. It's a tube-lovers's paradise.


As a further example of tube schematics and simulation consider the circuit below. It is a schematic of an amplifier from the same GE tube handbook.
12AX7 Linear Amp
Here is the schematic rendered in MC6 using the 6L6 as a substitute for the 35C5 pentode.

12AX7 Linear Amp
Here is the transient analysis showing the input 20mV P-P, 1KHz signal and the resulting output voltage across the simulated speaker load.

12AX7 Linear Amp
Here is the AC analysis showing the dB value of the output voltage across the speaker load, RLOAD. Notice that it shows about 41 dB, the same amount measured from the transient analysis waveform.

12AX7 Linear Amp
The Duncan models should provide a consistent and useful basis for analyzing these old curmudgeons of technology. The basic 3/2 power model has been elaborated to include the change in anode resisitance and the reduction in mu at large negative grid voltages. It also takes into account the anode current limiting that occurs with high positive grid and low positive anode voltages.
 
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