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Audio Research D70 mark1 + schematic

Hallo ! I´m trying to repair a D70 from 1983 . It has a 6DJ8
which determine the "workingpoint" for itself and the following two 6FQ7 tubes for each channel . This poweramp has no solid state parts and the cathodes of the 6DJ8 have two 1,5k resistors connected to each cathode ...... not 110 ohm and 511 ohm as mark 2 . I would very much like to find a schematic for this version of the D70 . ( The two 6FQ7 tube
in each channel have just two 6K powerresistors from their cathodes to earth ...... no other resistors as in version mark2 ) Regards Stewen
stewen1
stewen1 OP
9 posts
 
Thanks for answers ! Well , the schematic at www.arcdb is
an early mark 2 vesion with R13,R14 511 ohm and R12,R15 110 ohm . "My version has 1,5K for these resistors and its very
sensitive when I´m trying to set the +90V with the trimpot.
Can´t read the value of the trimpots ( four total) but when I measure it might be around 20K . The mark 2 version has 5K trimpots and I think it is much easier to set the "workingpoint" for mark2 amps. Do You think I should try a
modification here ? As I have found there are at least three
or probably more versions of the D70 model.
daveyf's avatar
daveyf
1,174 posts
 
Stewen 1, I don't think there are multiple versions of the Mk2. My D70 was updated at the factory to Mk2 status, which the factory still has record of.
You might check with ARC, as previously suggested, to get more info on your amp....just give them the serial #.
pmotz
375 posts
 
I wasn't inferring Audio Research service isn't good, just that I doubt they would "give" you a schematic. They may be more than willing to sell you one, if they have it. I assumed Stewen1 was looking for a quick and easy freebie, so that's why I made the comment. Since the dawn of (Audio Research) time the only way to contact them was on the phone or snail mail, no e-mail, let alone downloads. I hadn't been to the Audio Research website in a while, I normally go direct to ARCDB since there is more information there, but I took a look just now and was surprised to see they now offer downloads of manuals. Welcome to the 00's Audio Research! (I'm being facetious). For Stewen1, the bad news is the D-70 is not included.
czarivey
4,494 posts
 
What are you trying to fix? Maybe you won't need schematics.
stewen1 OP
9 posts
 
Thanks for Your answers ! Well , I might manage to fix this amp without a schematic .... the MK 2 schematic is a good help
even if it differs some from this amp , many values are the same. I have soldered a 3K resistor in parallell with each
trimpot to slow it down and make it less sensitive. Now , with
new NOS Siemens E88CC its very easy to set those +90VDC .
Tomorrow I´ll put in the new 6550 Tungsol reissue powertubes
and set the current to 60 mA or so . I have some problem to
order new 800-1000uF/450V caps from Mouser . And that 530uF/150 V cap too . Another question : is it silly to
spray a trimpot with oxidecleaner ? Or/and contact protect ?
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