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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: Audio Research D-70 (And D-40?) posted by thoriated_tiger on October 26, 2004 at 10:24:49:
I have owned both of these power amps. I currently use a pair of D70mkII in my set-up. I concur with Bambi's observations; ARC amps of this vintage are amongst ARC's finest offerings. Just not talked about much these days. Good for anyone looking to pick-up one of these gems cheap. There are (3) D70s on Audiogon at the moment!The D40 was built at about the same time as the D90 and D160. WZJ brief flirtation with the 6L6 output tube. This entire series of amps from ARC was probably their worst offering. White and bright would be the best way to describe the sound. In comparison to the the next series, i.e. D70/115/250/M100, the D40/90/160 lacked a great deal of resolution. The D40/90/160 really cheaped up on the power supplies. No screen regulation, no front end filament regulation, etc.
The D70 was also the first amp to use the 6DJ8 for input tubes. It also used an improved input/driver stage versus the D40 and has a more sophisticated power supply.
The plate voltage on the D70 is 430V. Biased at 65mA, this amp is very gentle on output valves runing them at about 70% of rated output. And it is reliable in the extreme. I did manage to smoke a D70 years ago when i installed Chinese made 6550. Lesson learned. Output valves need to be of very high quality. Current production Svet 6550C work nicely if they have been screened and matched properly. I would avoid Chinese valves at all costs. Some state the QC has improved with Chinese output valves, but burn me once..........
The amp allows for adjustment of output tube bias, DC balance and AC balance. A screwdriver and VOM is all you need for bias and DC balance adjustments. AC balance requires a few more tools! Once you get familiar with the amp, adjustments are quite easy. I am constantly rolling tubes on the input stage requiring readjustment of the DC balance. About a 60 second job.
Tubed correctly, the D70 sings like few amps can. Input tubes on this amp make-or-break the sound IMO. It can go from about as sterile and lifeless as you can imagine, to overly lush and romantic, all depending on the input tube selection. I would suggest good NOS for the 6DJ8 tubes, Amperex Bugle Boys being my favorite by far. NOS 6FQ7 can be had cheaply and any high quality example will work fine. They are used in the cathode coupler and driver circuit. I don't hear any sonic difference with this tube be it a RCA Clear Top, Sylvania, GE, etc., so go with what is the least expensive.
The mkII version is the amp to have. The original D70 used 6DJ8 for the entire input/driver stage. The mkII revision changed the driver stage to 6FQ7.
Make sure the B+ caps have been changed recently, or figure that into your price. Given the age of this amp, if the caps are original they need to be changed.
Sorry to say, I use my D70s with Quad ESL and Hartley woofers. It has been so long since I had my K-horns I can't really comment except to say ARC amps with K-horns sounded great! I just like the ESL better!
Good luck.
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- Re: Audio Research D-70 (And D-40?) - kentaja@yahoo.com 13:07:14 10/26/04 (0)
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