Thoughts on Audio Research D70

Indeed the D-115 Mk 2, which I owned for several years and is currently used by a friend in his system, has great bass drive and slam and is very dynamic HOWEVER it has less control and definition in the low bass than my current amp or some others I have listened to in my system. Also the presentation is a bit less airy, missing some of the ambient detail of some more resolving amplifiers. The D70 and D115 fall into the general category of "classic tube sound", a little rounder on the leading edges and thus can sound a bit fuller AGAIN a preference issue as often is the case in these matters. When more resolution is gained poorer recordings can come off as harsher than with a somewhat more forgiving amp. To be honest I could easily live with his amp as he has owned it for 12 years and done quite a bit to enhance its performance, again a great choice but still not as ultimately resolving as some that I've had in my system (all OTL's btw) but not enough of an issue to fret over for sure. Preferences and taste always comes more into play than absolutes but on balance these are truly excellent products and have aged quite well.

Thanks for the opinions. Now to find an old beat up unit for an affordable price so I can do a complete rebuild.

Found a D115 mkii. Can't wait to hear how it sounds.
Will definitely verify each test points voltage and go through the usual hexfred/schottky diode mods and coupling cap upgrades... then triode of course.
The circuit begs for a better driver tube than 6FQ7.
Will see if filament supply can support 6H30 (driver and power tubes have AC filament).

Johnsonwu, I will be very interested in your outcome after you have modded your D115Mk2. WZ Johnson got the circuit very right, IMHO. Changing what he designed could be a risky business, OTOH I applaud your experimentation.

Just the throw my 2 cents in, I'm not a big fan of Hexfreds. They can be very problematic down the road. One the other hand, some good soft recovery diodes in the filament supplies would work nicely, (non-Hexfred types). Also because 6H30's pull quite a bit more heater current I would avoid them in that amp least you over heat and damage the heater winding of the power transformer. Although the transformer might still be available from ARC, it is quite expensive. Instead, replace the stock coupling caps as well as the filter caps if they're old, and bypass them with good film caps. Make sure all the tube sockets are clean and tight, the 6FQ7's triode halves are well matched and the D.C. voltage around the 6FQ7's are properly adjusted. Check that all the voltage regulators are functioning properly and quiet.