I've had very good success with Andy at vintagetubeservices.com. Knowledgeable - extremely, opinionated - yes, accessible - you have to call him but he answers when he's there which I've found to be usually and he's happy to talk at length, quirky - a bit, we could stand a few more like him. I think he tests the bejeezus out of everything he ships, he has lost sales by steering me away from tubes he thought wouldn't be an improvement over what I had. His prices are very reasonable given the quality and they are less than a few other unnamed merchants with fancy websites.
