It's off South Lamar. Bill Webb is the amp tech/Builder. Eric Johnson takes all his amps to be worked on there. I got to meet Eric about a month ago when he was taking in his 67' Marshall head into be looked at.
Austin Vintage Guitar
1112 S. Lamar
I'll second Austin Vintage Guitar. That's where Eric Johnson often takes his equipment or so I've been told. I met Eric Johnson there once, and a buddy of mine met him there a different time and said EJ was having an amp worked on. I don't know the guy's name, but the owner is really nice. They also have great equipment for sale. That place is top notch. They did some work on two 1960's amps I had and got them to sound better than when I bought them.