Audio Research D160

Hi,

I can buy a Audio Research D160 but I can't find very much information on this AR tube amplifier.
I did consult the ARCDB pages and the Stereophile review of the D160B but that's about it.
First of all how can I discern between the various (possibly only two the D160 and D160B) incarnations?
Does anybody know more in depth about possible problems, weak points or anything else about this amplifier.

Thanks in advance,

Robert