Buy from ARC, tubes from others may be matched, but they aren't matched at the exact current draw the amp expects to see. You could have a matched set from another source that isn't with-in the range the bias can be adjusted on the amp. Unfortunately ARC isn't divulging what parameters they are looking for in testing/matching tubes, so you don't know what current draw specification you want all the tubes to match. I've bought several matched tube sets from other vendors & had quality control issues. Output tubes you might get by with from other sources, but input/driver tubes need to be exactly what the amps looking for, or you'll never get the input/driver stage voltages in balance with-in specified parameters. My understanding is Kevin Deal doesn't sell tubes for audio research power amps (too many come back as returns)I, from personal experience, don't trust him & you won't find any negative feedback on this site because A-gon wants his advertising dollars.I've personally had my negative feedback for upscale not published on A-gon, without explaination or reply from "management". I'd definately recommend ARC tubes sets in arc power amps.I've retubed various VT100 series amps 3 or 4 times & wouldn't even attempt a complete retube with tubes sourced elsewhere. Getting the input/driver circuit with-in specs is a major, frustrating effort, because changes to one adjustment point affects the other adjustment point & visa-versa, a constant moving target!