Rocksonics has released Triode, a free Class-A vacuum tube preamp in VST plugin format for Windows.
Here’s what they have to say about it:
“Triode” is a simple VST Plugin (1 control) that generates the asymmetric transfer characteristic of a Class A Triode vacuum tube pre-amp. The effect adds both even and odd harmonic distortion which creates the characteristic tube “warmth” that is NOT generated with filters.
“Triode” can be daisy-chained with the Rocksonics “Saturator” plugin (listed below) to emulate a Class A pre-amp followed by a push-pull output stage.