I had a D70 MK11 for about five years in the mid-80s. Excellent sounding amplifier with very few sonic flaws. My unit was totally reliable. The unit was very critical of the 12AX7 used on the input. If the tube was not quiet (LN or SLN) the sonics suffered as well as the life of the tube. After I changed to RAM SLN tubes all my problems went away. The D70 in the mark II version this is still one of the better sounding amplifiers available.
Thoughts on Audio Research D70
I recently saw a very well priced D70. If I remember back in 80's these were highly thought of. Having no chance to hear, what do they compare with today or do they?