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Arc D90, advice needed

E

Espen

New Member
Hi,
i have my hands on a Audio Research D90 from the mid 80´s, currently out of operation and in the need of new tubes. I have never heard this amp before and hope for a review and advice from you. The guy selling is asking for about 600usd but i do not know if this is a fair deal or not. The amp i need are going to run a pair of Tannoy horns(15" hpd)
Thanx for any help!
Espen
(i have posted this before on another forum but with no ansvers)
 
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bluebook says,

AUDIORESEARCH PWR, D-90 TUBE
Manufacture Years: 1980 - 1981
Power: 90wpc
MSRP: $2,200.00
USED: $765.00 (used prices tend to be always on the low side)
 
D90 is mighty! I assume it is broken? Kinda high price for a unit that you can't listen to. Once fixed you will be very happy with the sound.
 
it is a killer amp .but if it is broken you should be experienced if you fix it
the voltage is up to 575 volt so be carefull !
 
The D90 is a great amp. I used to know a guy who had one, and I loved the sound. But, this does not sound anythng like a "classic" tube amp. It is not particularly "tubey" sounding. It is a much tighter, and brighter sounding amp than most tube units. It's strenghts are its newtrality, transparency, and great imaging, with just slight a touch of tube sweetness on top.

Please note however that the D90 is technically a hybrid unit, as it contains a couple of op-amps inside of the circuit (not just inside the power supply). $600 would be a great price for a working unit. For a non-working unit, that is probably still reasonable.

If you decide to pass, please PM me. I'd certainly jump at such a deal, but I'm also very good with a soldering iron... :thmbsp:
 
Thanks so far!
I´ll check it out closer to see if ther is something more wrong than just the tubes.
Since i have to re tube the amp, should i stay with the original setup or do you recommend other makers/brands/"ethnic" tube alternatives?
Cheers!
 
instead of 6550 i use svetlana kt 88 the small signal tubes best ei 6cg7
the regulator tube (in the middle) should be a 6550
you should know how to bias tubes audio research is not userfriendly in this point
 
That's a lot of horsepower for the Tannoy drivers. You might consider something with lower output as they are fairly efficient speakers.
 
junkaudio said:
instead of 6550 i use svetlana kt 88 the small signal tubes best ei 6cg7
the regulator tube (in the middle) should be a 6550
you should know how to bias tubes audio research is not userfriendly in this point
Click to expand...
Sorry; there are no 6550s in the D90 (except possibly inside the power supply) It uses 8 6L6GCs instead. You may have a hard time findiing the original brand of 6L6s to use though. If you want to try tube rolling, the KT66 is the best match for this tube.

Now, you need to understand that this is an especially dangerous amp to work on. Chances of releasing the smoke, or getting electricuted are much higher than with most tube amps. The open circuit board layout, and HUGE power supply capacitors means that it is really easy to blow things up, or kill yourself, if you are not extremely careful.

I have serviced one of these before, and I cn tell you first hand that it is very tricky to set the bias on the output tubes without burning yourslelf. This is because the bias pots, and cathode resistors are both located inbetween the output tubes, and these tubes get extremely hot! It is also rather tricky to get your test leads clipped onto those resistors for adjusting the bias.

I generally do not say this, but I absolutely do not recommend that a novice attempt to work on this particular unit. It is challenging for a seasoned tech not to get burned (or short something out) when setting the bias on this amp. ARCs can be great sounding amps, but they tend to be somewhat unfriendly to servicing.
 
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junkaudio said:
checked again on www.arcdb.ws the outputtubes are 6550
i think arc always build their amps with 6550
Click to expand...
Then either the database Database is incorrect, or we are talking about a different amp. I have the schematic for the D-90B amp, which I just pulled from my files to double check. It clearly shows 4 6L6GCs per channel as the power tubes.
 
maybe they build 2 versions one with 6550 and one with 6l6
i saw one d90 with 6l6 on ebay
i own 4 arc so far :d76 d70 classic 60 all run on 6550
when you check partlist on www.arcdb.ws and picture you see 6550
 
orion lists 2 versions of the D-90, here's the other...

AUDIORESEARCH PWR, D-90B TUBE
Manufacture Years: 1981 - 1985
Power: 80wpc
MSRP: $2,700.00
USED: $875.00
 
junkaudio said:
maybe they build 2 versions one with 6550 and one with 6l6
i saw one d90 with 6l6 on ebay
i own 4 arc so far :d76 d70 classic 60 all run on 6550
when you check partlist on www.arcdb.ws and picture you see 6550
Click to expand...
I agree that the vast majority of ARCs have used 6550s. This is one of those rare exceptions. Another that I know of was the D-50 which used EL-34 outputs.

And remember, a set of four 6550s in class AB1, push-pull pentode operation usually produces about 140 watts, not 90...
 
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I have found this information on AudiogoN that clarifies the question:

There are three versions of the D-90 : 90 ,90A and 90B.The obvious differences are power tubes ( 6550 in original and a, 6L6GC in b) and power output 90 in original and a ,80 in the b.

Regards
 
There were two different versions of the D 90. The original had problems with the position of some wiring and the delay turn on to the output tubes could cause problems. It’s best if bypassed. The later version used 6l6 output tubes. Sounded better at 70watts. All in all a decent amp with the typical ARC sound characteristic
 
Had a slightly older D-70 for a few years. Based on my experience I would definitely recap it from end-to-end. Mine blew a small cap that burned a spot on the console it was sitting on at the time. Lucky it didn't burn the house down. But, it did sound good.
 
MX117.MC7150 said:
Had a slightly older D-70 for a few years. Based on my experience I would definitely recap it from end-to-end. Mine blew a small cap that burned a spot on the console it was sitting on at the time. Lucky it didn't burn the house down. But, it did sound good.
Click to expand...

I'm still using a D70 MKII in a secondary system. I love ARC :)
 
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