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AUDIO RESEARCH D-76A

I am new to this trade so bare with me if I ask dum questions.
I have a AUDIO RESEARCH D-76A power amp that I been using for few months now. as you probably know this amp has the most tubes than any other tube amp that I can remember. the middle of the amp are four 12AX7. I notice that one of the 12AX7 [middle top] are not lighting up nor hot. so I had all the sockets replace but still no light nor hot. I was told that its normal. how could it be? will this de-grade my sound? please enlighten me. I will appreciate any advice. thanks
torogi
hifigeek1
770 posts
 
What is the V number of that 12AX7 tube and I will investigate it for you.
torogi OP
6 posts
 
I believe this are the original RCA tubes unfortunately most of the white numbers or letters are erased. all I can find are the red letters/numbers that says RCA afc 12ax7/ecc83. how ever I tried other four tungsol 12ax7 with no improvement. I just fund other symtom. Iv'd been running the amp for at least
3 hours when all of a sudden the right channel made a crackling sound. sense
that the right channel volume went down. until now I'm trying to figure it out. the left channel is 80% louder than the right channel. I will appreciate any advice I can get. thank you very much.
Art
torogi OP
6 posts
 
Thanks Bifwynne, I will give him a call at ARC.
bifwynne
2,206 posts
 
Torogi, if you really want to keep the amp, I strongly recommend at this point that you send it back to ARC for evaluation and repair. It is well known that ARC fixes everything they ever sold. I'm not an electronics techie, so I can't say whether your problems will be costly or not to fix. Who knows, maybe some old passives (e.g., caps or resisters) are bad. I believe that the D-76A was built in the mid-70s, so it could be 35 years old by now. Perhaps Hifigeek can weigh in if he has any ideas, especially what could be wrong and how much to fix. Good luck.

hifigeek1
770 posts
 
Well you could always send it to me as well if you are close to the west coast. Actually, I have refurbished quite a few D-76A's in my time and in fact when the amp is done, it sounds better then new. The reason is, all the filter caps are replaced with non-twist lock caps. The twist locks that came standard with that amp have high ESR (equivalent series resistance) not a good thing for a filter cap to have. Unfortunately, that was all that was available when that amp was manufactured. All the new caps have little adapters so they fit in the circuit board spaces for the twist locks. Also, there are a number of zener diodes used as voltage references, and those tend to drift over time. When the amp is finished, and retubed, it is one awesome sounding amp. Hopefully, one day, ARC will make a commemorative version of that amp as it's truly a classic. I keep pushing them to do it. I think it's time to ask them again. lol
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