Thoughts on Audio Research D70

Hi Johnsonwu, I may be misunderstanding your intent. If you are not planning on changing the circuit that is inherent in the amp, then there are no real risks that I can see.
BTW, I agree with you that the circuit is superior to the Classic 120's and the VT series..... this has been borne out in the listening tests that I and my a'phile group have conducted vs. the VT series and the Classic 60 that we also AB'ed against. ( presumably the Classic 120 is the same basic circuit).
I have yet to hear a better ARC amp in the mids than the ARC D70mk2, even in the ARC VS series of today.

The Classic series had triode configured output tubes. This tended to make the output tubes last longer and gave it a sweeter presentation. I believe the front end was fet transistor up to the driver tubes. Very different topology from the D-115mkII

@Hifigeek1: Yes indeed triode vs NON-Ultra-linear fixed bias tetrode mode. But same B+ @ output stage.
420V B+ is a bit low for my liking but with 4 tubes per side power should be more than enough.
I have every intention to convert that to triode at a later stage, after I am done with the caps and diodes.

I had the CL120 and CL150s before. CL120 at least has a tube driver stage (different plate voltage from D115 though). CL150 is just raw muscle.

Oh well. So much for the exciting anticipation for the amp.
Seller allegedly got talked OUT of including the original outer box by the FedEx people and the unit was shipped in the inner box only with less than a few pages of newpaper in the box so go figure what happened.

The CL-150 was a totally different animal and frankly pretty average by today's standards. It started life as an M-300 and used Chinese coke bottle 6550's which at that time, were just awful. Their were no Russian 6550's at that time, and the Sylvania 6550 was history. So the only choice was to use the Chinese 6550. The Chinese tubes would fail after a few months, but the heaters would still work. So basically the light was on but no one was home...ARC decided to change the amp to the Classic series and changed the output configuration to triode making easier on the Chinese 6550 output tubes. So it became a CL-150. It's got great slam and sounds good and is miserable to work on. The cooling fans blowing on the fets and tubes while the amp is on is not an advantage. Cooling tubes yes, cooling fets no. Funny thing is a modified M-300 to triode have bigger transformers then a stock CL-150.