Audio Research D-115 MKIII tube amp..

I had an ARC D115 mk II for four years in the late 1980s and early 90s. It was used to power a pair of Martin Logan CLSes and was preceded by a Beard P101, and then a Spectral DMC10-Delta.
This amp had a very clear and clean midband with that liquid ARC way with soundstaging that is so compelling. It was not particularly defined or extended in the bass, but not unpleasant. It's upper range performance was pleasant, but not particularly extended or powerful. The upper harmonics that allow you to determine what certain instruments are in an orchestra were MIA. Of course, the CLSes are particularly difficult to drive, so I am certain your results would differ from mine. I had no service issues with my unit during the time that I owned it.

Yioryos is right there was no mkIII.

I am currently using the same D-115 mkII that I purchased new in 89 or 90. I have had a few tube failures, but have just soldered in new resistors I got from Leonard at ARC. It is not that big a deal.

I don't really care for burning my fingers when biasing the tubes, but it is also not that big a deal. However, you will need a good (~$150) multi-meter to do so.

I am driving ML CLS's from an AI 3A. Still love the sound of this amp.

I owned one and really liked it a lot, great staging, a lot of umph in the bass but as noted by Silab, not as controlled as what you can currently find albeit at a price. The upper frequencies in comparison to the better tube amps out there currently is also not extended and I always noted a glare I couldn't completely eliminate. It uses a lot of power, about 400 watts at idle, is a royal pain to bias, you need a long probe to get between the cluster of 4 outputs per channel and the bias is quite high at 65ma. As far as I'm concerned for 1K you aren't going to find a new tube or ss amp that will touch this level of performance at this power rating cause the bottom line is it makes music and can power quite a few speakers out there.

It cost 3k new and production stopped in 1989, right before introduction of the "Classic 60". I like the D-115 Mk 2 better myself, the Classic had a bite that the all tube D-115 didn't. Maintenance could be an issue but it is a good design and of course you always have the support of ARC. I sold it about 4 years ago to a friend that still has it along with an SP-10 Mk 2. I always enjoy listening to his system.

I like only to add that this amp is really a lot sensitive to tube rolling.The first great improvement is to get 3 real nice nos 6 dj8s in V1, V2,V3 pos.(I have Amperex globe logo early '60) ,these tubes in this position can share a lot or their sonic,well known virtues.The amp gets completely to another league, no hint of glare at all! In my ex. kt88 EH can controll the bass well enough that mids and highs from Amperex are really shining, staging is great, music flows.
I tried VT 130 SE, then VT100 mk2,both with stock tubes,simply no contest.
Sorry for my poor english.