It is a 6GY6 kit that I purchased from someone on the forums, but I forget who was selling them. I made a few mods to suit my purposes.
I use a program called Winamp with the stereo tools plugin to feed my transmitter as it has a real nice AM transmitter setting that provides near professional quality audio and with the line in plugin I can feed anything to the transmitter and get the same near professional quality audio. Sounds similar to if not better than some AM stations.
Almost any AM radio will pick up this transmitter quite nicely.