Thoughts on Audio Research D70

No flaming. My attitude about spending gobs of money on NOS tubes is kinda like buying expensive flowers. Sooner or later there going to die...LOL I'm not a big fan of NOS output tubes. The D115mkII was designed around the Philips/Sylvania 6550. Look for a set of those. BTW just because the voltages are ok on the amp doesn't mean the voltage regs are quiet. That's important too. Noisy voltage regs. have a negative effect on that amp. Also, there is a B+ reg and a buffer reg. Make sure the voltage differential is the same or close to the circuit diagram. If the power supply caps are more then 20 years old, replace them. All new caps will make the amp sound better especially in the bass provided there's nothing else wrong with it. There are a few axial caps scattered throughout the amp. Replace those as well. On top and underneath. There is also a 27K ohm resistor near the main filter caps. Make sure it measures 27K. Those do open with tube arcs. There should also be red cap plugs on the capacitors. The support bars always get bent because people try to lift the amp with them and their aluminum. You can remove them and straighten them out a bit to get some of the kinks out. Use a rubber mallet, however the rack handles will come off too. Do one at a time. I strongly suggest you make sure that amp is in good working order before you attempt to modify it.

@DaveyF: No other offender. I am comparing it with my 6 other amps in the room.
Vac Phi 70 monos
Counterpoint NP220 Premium gold
Jolida 502 thats "re" modified from an already modified unit
just to name a few.

@hifigeek1: Thanks a lot for the suggestions.
I myself hate using NOS power tubes, I pity those who generic Sovteks and Svetlanas remarked as whatever the hell reissue and give them names like Black voodoo and blue snake oil. Chinese tubes even to this date are a complete joke. Just sad to see the feeding frenzy for those 50 year treasures. I myself use Svetlanas or Sovteks. They dont sound as good as the NOS stuff but with balancing and tweaking of the gain and driver stages I can live with the imperfections of run of the mill and reasonably priced power tubes.

Thank you very very much for the pointers. I scope the regulated B+s carefully. Thanks for the tip on measuring the 27k resistor. Been bitten before by a few resistors on my VT130 which measured wierd...disintegrated when I tapped them with a chopstick.

I am giving up on Hexfreds on this one, no way I can safely mount them unless I can find ones in smaller than T0220 package.

Thanks again.

@Hifigeek1 you are talking about the 270k drop resistor R75 thats a protection bleeder across the main B+ filters right? I cant seem to find a 27k in the schematic. Is that a WW or a Carbon comp?

Hmm I think I found it, goes from ground to pin4 of TL071, big 7W WW resistor. 26.4k and holding stable no change with tapping.

That's the one. Also make sure you measure 10 ohms at ground to common tap at output transformer.