Audio Research D70 mark1 + schematic

Stewen 1, do post again once you have had a chance to listen to the amp. I will be VERY interested to hear your thoughts.
IMO, this amp is one of the very best low power amps that ARC made and is still HIGHLY competitive with the latest offerings.

Well , one more difference in this amp ( being a mark1 or
mark 2 or something in the middle...? The anoderesistors for
the last 6FQ7 tubes in each channel is only 33Kohm compared to 62Kohms in the schematic I´ve found on the web..... ( a mark 2 version ). Could my D70 be a very early version ? ( but it´s
made 1983 )... ? Also the amp I have here only has one couplingcap 1 uF ( wondercap). On the schematic I have there are a 15 nF cap in parallell with the larger wonddercap.
I have a little stock of k40Y caps from Russia. Do You think it´s a good idea to add a k40Y , 15nF/630V in parallell with
the total number ( 4 ) of these 1 uF wondercaps ( each feeding a 6550 ) ? Not necessary , but it would be interesting to find a schematic on the web which is a "copy"
of "my" amp ..... Stewen

Stewen 1, I wonder if you have an earlier version i.e a Mk1 that was semi-converted to a Mk 2 by someone other than ARC?

I believe that unit shares a similar power supply with the D115 in which case there are indeed solid state devices in the voltage buffer circuit unless somebody removed them. It's important that they be functioning properly or the output of the amp will be noisy. It consists of 2 bipolar transistors, D40k1, a TIP device, and a TLO71 IC. When I get to my office I can give you the proper working voltages. There should be (3)6922 inputs followed by (4) 6FQ7/6CG7 drivers and then the output 6550's. In the regulators there is (1)12AX7 and (1)6550.

Thanks for Your answers ! Yes , Hifigeek 1 ! All components You describe is the same in this amp . I´d be very happy if you could give me the voltages you mentioned. Stewen