Audio Research D-350B - when is ginormous just too damn big?

w1jim

I can fix it but good...
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Picked this up from AKer Kenwood Man in Philadelphia earlier in the week - it was a Barter Town deal.

This thing is one MF'ing monster!
Witness-
105 pounds (I used a block and tackle to hoist it onto the work cart)
Over 250,000 mfd of power supply caps
32 output transistors
350 watts per channel into 8 ohms
3 fans
3 big honking meters

Should suffice for some serious listening and perhaps a little welding on the side.

The bad-
The power switch was snapped off (easy fix with a stubby bat handle minitoggle switch).
Two of the meters are missing the glass (minor)
One meter is missing the needle (a bit of a challenge)
Three meter bulbs out (yawn, 24v bayonet incandescants)
And most critically - one channel doesn't work - now that's going be a PITA to track down. I'm guessing toasted output transistors. I've read that I can use some on semis to replace them, to be determined.

Getting at the transistors is going to be fun - looks like it requires the removal of both side panels and then it should splay out - we'll see soon enough.

Once I get this operational I have a few mods in mind. There are a few tantalums that will probably get replaced with audio grade electrolytics, it loos like the driver PCB has some opamps so I may update those, the RCA jacks and speaker terminals look a little wimpy so they'll get upgraded.

Stay tuned, this one's going to be a project - at least the manufacturer is still in business so I may be able to get a service manual.


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The definition of BEAST!

Wonder how much of the grid you will knock down when you fire it up.

Good luck with your restoration.
 
Now that, is a big honkin' amp!

Hell, recapping the power supplies would require refinancing the house!
 
I can't believe that someone may have managed to blow the outputs on that!

Of course, I have met some people that could damage an anvil with a piece of spaghetti!
 
Sound like you're going to go down this road, I have an very clean unit also with one channel distorted, sat for years in a box. My local ARC dealer told me it's not the parts cost (or shipping I live in the same town as ARC ) it's the labor cost, apparently theses are a not only a beast to lift but a beast to work on as well. I will look forward to your progress reports, maybe I should reconsider having it repaired, maybe by someone other than ARC.
Good Luck,
John
 
At least I charge myself a lower labor rate!
I'm hoping it's not an issue withthe various sealed A/R modules - those could be mighty expensive and would be hard to diagnose.
First step will be to see how far the signal gets - at least I can compare the good and bad channels.
 
Good luck with the repairs, and hope you get it up and running. Looks like a real beast.
 
If ARC fixes it you will have a warranty on the repairs, If you fix it......
...I'll be able to maintain a positive bank balance and gain in the satisfaction of a job well done :banana:.
Besides - I give myself a lifetime warranty on all repairs I perform.
 
"I can't believe that someone may have managed to blow the outputs on that!"

"Anyone who believes that they have made a fool proof device is not reckoning with the ingenuity of fools." anon.
 
Yep, it's a monster inside.
The bad channel folded down...


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Oops, miscounted - 32 TO-3 transistors per channel (plus 2 drivers)...


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Umh, hello, did you guys ever hear of transistor sockets?

Each TO-3 is soldered into place, put first I had to unsolder the PCB's with the power resistors :scratch2:.


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Hmmm... this is beginning to look like it'll keep you quiet until the Winter... :thmbsp:

Thanks for posting, this is going to be an epic :banana:

:lurk:
 
No one ever accused ARC of doing anything "small" or "half-assed." I do believe they've been accused of being "bats**t insane" on multiple occasions... :D

Very interesting project, can't wait to hear how it turns out.
 
It's very complex, isn't it? If you get this working, you will have a great sense of accomplishment. We'll cheer you on, you will need quite a bit of encouragement from the looks of it.

The transistors should be easy to get. Finding the fault - answering why it blew up maybe the hardest part - I wouldn't shotgun this amp, way too much work!

You had the confidence to take this on, so I am guessing you ought to be able to do it :)

:lurk:
 
You had the confidence to take this on, so I am guessing you ought to be able to do it :) :lurk:
We may be confusing confidence with with over confidence.

Very interesting project, can't wait to hear how it turns out.
Now that's an understatement.

Tested all 32 output transistors - they're all good. Fortunately I didn't have to remove the transistors; once the daughter boards were removed the transistors were isolated from each other.
I also removed the 2 driver transistors and they tested good.

Next step will be to start tracing the signal on one channel and then seeing if it's there in the corresponding location on the dead channel.

I'll be using an audio signal generator and my scope.
 
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