Audio Research D70 mark1 + schematic

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

The voltage on the collector of TIP41 is 335Vdc. On the emitter of the TIP41 it's 327Vdc. They may vary a bit but the 8Vdc difference voltage should be the same. If it isn't, the buffer has issues. If you are unfamiliar with measuring high voltages, do not attempt this. Sometimes the probes can load the buffer down. It is not necessary to have the output tubes in the amp when you measure the buffer voltages, but you will need a variac to drop the line voltage to 115Vac if you remove the output tubes as a load will not be on the main filter cap bank and they may see an over voltage.