Audio Research D79

I just aquired a Audio Research D79 amp.Can any one tell me any history of the D79.I would like to know the years they where in production and the differances in the orgiginal,B,C and the C Mark2.Also what brand tubes sound best.My D79 is the first version.
The D-79 first appeared, I believe, in 1979 when I worked for San Jose's Garland Audio. Sorry I can't offer more details, since I left the audio business in 1980, but I _can_ say that you have a superb amp, something that Bill Johnson put a lot of time and effort into.
Nice choice of amps, with minor work that unit will perform against just about anything. Unit is a pentode operated in ultralinear, with a HUGH power supply (in the neighborhood of 550 joules). The first series of 79's were not noted as an 'A' but are called 'A'. The 'A' version was a (not exactly) D76A front end with this power supply, the 'B' was designed with the D90 front end and the 'C' is designed around the D115 (and D115 MKII on the 79C-MKII). There is only around 25-30 79'C's, not sure about the others. Very well built and can deliver top performance with very little maintenance. Keep one thing in mind...ARC amps work best with top quality tubes. I'm currently working a large one over after someone ran 'China' type tubes..resistors and circuit took a hit when the tube(s) let go. Get Sevtlana 6550 or Kt88 or for the best protection look at ARC's tube..costly but most reliable. I'm not saying others are inferior just appropriate quality when it comes to these tubes..Ram, others as well will work. Also, the regulator tube helps to have high transconductance. Down side to this amp is the power out of 75-80 watts per side, can be small or huge if coming from the single ended camp. Holman, e-mail me and we can get in touch, I will explain more about this superb amp. KMc.
Yeah I saw those D79's recently advertised and was tempted. You have yourself one fine amp there and I doubt you can do too much better as Alex says. That amp has a legendary midrange if you haven't already discovered. I heard one once years ago and it never left me like most of ARC gear from the "all tube" days before they went down the hybrid road. The D-79 is probably at the top of all those esteemed amps. Enjoy!