Thank you very much Eric, now I can work !
I put the file "new_triode" and "dmtriodep.lib" into the folder where I saved my xxx.asc, for example:
1. open lts and create new schematic
2. save it whit xxx.asc name in my folder xxx.asc
3. copy and paste dmtriodep.lib and new_triode file into my xxx.asc folder
That's the only way I can see your file, because I tried to put dmtriodep.lib into C:\Program Files\LTC\LTspiceIV\lib, but seems that the ltspice doesn't find it!!
If I copy the dmtriodep.lib in a folder where I save my project, I can find the symbol!
I would like to work whit a pentode (generic) also, but in your library there aren't any pentodes models, do you know where I can find some models and how to work whit them? I loked in duncan amp's website, and I found some mdels, but I don't know how to test it!
And last one question
If I have a specific model, like 12au7, but I need a tube whit different characteristic (different mu, anode current, ecc..) can I modify the 12au7 parameters to have a new one model?