The AM Forum

Has anyone modeled a audio amp, such as the preamp of a Viking II, in LT Spice?

I don't know where to find tube models.

No I haven't, but look at this forum:

http://www.diyaudio.com/forums/tubes-valves/148630-need-help-tube-models-ltspice.html

By the way, this is an over-the-air recording of me with my stock Viking II and a D-104 right in to the Viking II, courtesy of Jeff W2NBC:

Here is some info on tube modeling:


http://www.dmitrynizh.com/composite-triode-models.htm
 
http://www.duncanamps.com/technical/ltspice.html


Phil - AC0OB
 
 
 
 
 
 
 
 

For anyone else interested, I have several spice models of different tubes that I have collected and or created over the years. I also have LTSpice *.asy symbol files of the different parts for the schematic capture. There are: Single and dual (common cathode) diodes, triode, tetrode, pentode,  pentagrid converter (6BE6 type), and several sheet beam deflection tubes such as the 7360, 6ME8, etc.

Some of the models I have found were made up from semiconductor models, such as FET's. This has been common practice for tetrodes. I have some models from Ispice where the filament is modeled too and must be powered to get any current flow...a nice touch.  Personally, I prefer the mathematical approach where the transfer function is based upon a multi-variant equation, ie. Ib = F(Vp, Vg1, Vg2), etc. One approach takes data from points on manufacturer's graphs and then uses a curve fitting program to determine the coefficients of a polynomial expression. Once determined, the model is tested with a curve tracer circuit using LTSpice to verify the results. 

My model of the 7360 gave these results:

I made up an LTSpice circuit for the audio modulator of a Valiant.  I have not gotten the transformers modeled correctly yet, but the preamp works well.