New To Me AU-7900

leray1

Active Member
My TA-500 turned me into a fanboy so I've been hunting for an upgrade. Well, I couldn't pass up this AU-7900 on that auction site, of all places. Seller said it was untested and the description of how it was used and stored was a bit concerning, but I decided it was worth a gamble.

I got it today and tested it before cleaning by listening briefly to a record. Worked fine, not even a scratchy pot. It was just dirty, inside and out. I just finished cleaning it, and giving the pots and switches a de-oxit bath. Tomorrow evening I'll check the DC offset and the rest of the functions.

See here for Before Pics.

After Pics:
IMG_1926 by leray1, on Flickr

IMG_1933 by leray1, on Flickr

IMG_1948 by leray1, on Flickr

IMG_1939 by leray1, on Flickr

IMG_1919 by leray1, on Flickr

IMG_1957 by leray1, on Flickr
 
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AU 7900 is a hell of an amp. I auditioned one a few days ago , unrestored , and it sounded just beautiful. I imagine how it will sound restored.
 
Totally agree with Jomark,this amplifier is very underated. It sounds very good and the power is more then the rated 75watt.
 
Congrats on the purchase, looks like it is almost mint!

The 7900 is a very nice amp, somewhat of a rival to the 717

Cheers

John
 
It definitely cleaned up nicely. There are a few fine scratches here and there but I'm really happy with the shape it is in. I was expecting a few conspicuous flaws. My gamble paid off.

The DC offset is pretty good, too. R 14.8mV; L 21.8mV so I will get to hear what she can do this evening. I can't wait.
 
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Wow, this thing sounds good! And there is lots of flexibility with all the tone and filter switches. I had fun for a little while. But..all is not as well as I thought. There tone and filter switches need cleaning - I skimped on their intial cleaning because they are difficult to get to. And, the aux 1 plugs in the back are loose, or something. The cords need to hang to the left or no sound comes out. I hope to have her up to snuff by the weekend.
 
Cracked solder joints on the inputs is pretty common with these. Not too bad of a job to fix but it does require a fair bit of disassembly to get at them.
 
yours is a very clean looking amp!
I bought one a couple of years ago with a power switch that had been changed for a rotating power switch and so the face had been "adapted" (one word for it) :tears:
A year later I finally found an unadulterated new face for sale but the seller wouldn't ship outside of Canada so with the help of an Aker from Canada I was able to purchase it and get help shipping it (I still owe him a massive favour or something!) I haven't seen any 7900 faces before or after appear so i guess its a rare part to get hold of.
A couple of days ago found a new (old) power switch actually from a tu 9900 which appears to have to same part number as the power switch from the au 7900, here's hoping.
So after a long uphill battle I will be looking at getting it up and running at sometime in my lifetime and hearing what people say about the 7900 I am really looking forward to it. I think i saw some talk about the power switches on these having difficulty over time (why maybe this one was 'modified')so I may look into adding a relay between switch and power.:scratch2:
 
NICE AMP!! It reminds me of its cousins the AU-9900 and 11000. Sweet.

I think i saw some talk about the power switches on these having difficulty over time (why maybe this one was 'modified')so I may look into adding a relay between switch and power.:scratch2:

Don't use a relay! That's the hard way to go. Use a TRIAC as in this great thread. I suggest you read the whole thread and get the exact part recommended.

I recently finished my AU-11000 restore and had to rebuild the power switch. I was able to use one contact of 4, and to protect that I followed the TRIAC method as outlined here. It works great, not noticeable at all.

Be safe working with mains voltage!
 
I put it back on my bench last night and will be working on it as much as I can over the weekend. I should have gone all out on the disassembly to begin with but I was too anxious to hear it in my system. Now I'll be able to do a thorough inspection (I hear the glue used on these can be an issue :scratch2:) and cleaning.
 
Where into the switch housings do I direct the de-oxit?
If your refering to those 5 silver slide switches...
To get the deoxit where it will do the most good.Those switches need to be removed and disassembled. Otherwise you will just be wasting your time and deox-it. IMHO.
 
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If your refering to those 5 silver slide switches...
To get the deoxit where it will do the most good.Those switches need to be removed and disassembled. Otherwise you will just be wasting your time and deox-it. IMHO.

Is removal as simple as unscrewing them from behind the face plate?
 
Is removal as simple as unscrewing them from behind the face plate?

And desoldering from the PC board. Thats the easy stuff. Disassembling,cleaning and reassembling without destroying is the tough part.
 
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