I own a Belles 350A Reference amp with which I am blissfully happy. I recently sent the amp to Dave for service, and was able to make the arrangements with minimal fuss. No, he didn't always answer the phone when I called, but he usually called me back within a couple of days. He was also fairly responsive to my emails. It took about a month to get my amp back, but it was well worth the wait.
I get the impression that Dave's business (Power Modules, Inc.) is pretty much a 'Mom & Pop' shop. I know that he personally did the work on my amp, and I suspect that's the case with each piece of equipment that comes through his doors. If he fails to answer the phone when you call, or is slow responding to your emails, it's probably because he is BUSY WORKING!
I'm more than happy to accept the occasional slow communication with Power Modules, Inc. in exchange for the satisfaction of knowing that when I do speak with someone there, it'll be the man holding the soldering iron.