Audio Research D79C Amp

Recently I acquired for $1800 an Audio Research D 79C amp in really excellent condition, I would say a 9 out of 10.  It seems to have had very little use.  I had it checked out by a really good technician and brought up to spec and it really sounds gorgeous.  I am using it with an Audio Research Sp10 Mk II preamp into Proc Ac Response 4 Speakers. I know that we all hear reproduced music differently, and I tend to prefer the older Audio Research sound and am very happy with this combination.  I have found very little information about the series D79 amps and am wondering if some ot you experts on Audio Research could tell me a little more about this amp and where it fits into the D series of amps by the company. In the owner´s manual, the date on the schematics is November 1982, so I am assuming that the amp was probably built in 1983.  What I would also like to know is why for a 75 watt amp, the unit is so lage and heavy.  It weighs 85 pounds net.  Any further information or comments on its use would be most appreciated.
Cheers and many thanks in advance to all.
I have a D-79 (first all-tube version with no letter designation) supposedly tweaked by Bill Johnson himself for an Audio show at the time. It was my Father's amp, and he truly loved ARC gear, and owned it since the company started producing equipment in the early 70's (he first bought an SP-3A preamp and had bi-amped Dual 51 and Dual 75 driving Magneplanar Tympani I).  These D-79's are truly special amps and they don't make anything like this any more. I believe they were a statement amp for the time. The last time I used it was with my Magnepan MG 1.6's and to this day I believe it is one of the best sounding amps I have ever heard (and I have owned a few through the years). They are way overkill in their design and I believe they only ever made a handful. Anyway I believe you have a special and rare amp, and one of the few. Good luck. 
A classic SOTA amp in it's day! "No holds barred" design.

Will hold up to most any amp made Today IMO.

A "keeper" you will cherish, do not sell it!
back in the day TAS went on and on about the D79 and how great it was.

good for you!

just thought you might like to hear that...
ARC D79 & CJ Premier 1 are awesome, I know a guy who owns both and swears by them.

Newer technology now, but something about that sound from the era that’s missing.