Calling All Tube Gurus

I have Audio Research components and purchase my replacement tubes from them. All I know for sure is that they are very, very picky about their tubes and reject a large percentage of them.

Alvinnir2,

Very good observations/advice.  Some people get a bit too obsessed with matching.  A local dealer has a huge collection of used tubes that still test very strong and he "matches" them by finding tubes with the same internal structure.  That is it. 

I am "blessed" with running such rare and exotic tubes that there is no issue about matching; if they work that is as close to matching as I will get (I run 310, 311, 348, and 349 tubes).  If I ran more conventional tubes, I still would not go crazy with matching.  I could do matching the right way if I wanted to using something like the Amplitrex tube tester which can, if hooked to a computer, curve-trace the tube.  That really is the best way to match tubes, but it takes a lot of experience.  I can read the curves and I know what they show, but, I have no idea what is good enough or what is a close match.

"If you can determine that a tube was made in the same plant, has the same construction and date codes, how critical is it if the tube was made by Siemens and rebranded as an Amperex? "

only critical to appearance if appearance is critical

"I’ve heard people say that if a manufactures tubes are not up to their standards, THOSE are the tubes they send out to the other manufactures for their branding. Fact or fiction?"

nonsense AND fiction. 

tubes are identified by and perform/sound similarly according to manufacture. rebrand is only as important as looks. even within one production run they vary in quality.

"matched," unless qualified by "gain matched" or mention of emmisions testing, refers to tubes of the same manufacture and contsruction testing within 5-7% plate current at spec voltage (power tubes) or 7-10% transconductance (preamp tubes) or both.

as far as branding/label, if you want them to look the same then hey it looks good. what someone writes on the outside doesnt alter origin, identity, sound or performance, nor does it opertain to matching.

Even on the same tube type, factories tweaked their construction from year to year. Usually to save money. Some of these changes are visible, others may not be?

Anyways, we (I mean the collective "we" here, including me) probably let our audiophile nervosa run rampant too much. I've used pairs a tubes a few years apart with different internal construction.

Example 1: GE 3-mica black plate 5751 from the 1950s, but one from 1953 with the "silver clips" and the other not (from a few years later) - and honestly it sounded great (Rogue Apollo tube monos). The "silver clips" was the better tube but enough of its magic came through without an obvious asymmetry here. Of course I ended up getting more (many more) of the silver clips version for symmetry and peace of mind anymore. But if you've got a factory match, "similar" construction, and a good electrical match, it should be fine.

Example 2: Brent Jesse might even slip you a slightly construction mismatch if you're not careful. I got a pair of Mazda 12AX7 from him, one with shiny silver plates (the typical kind for this version) and one with matte silver plates and a different hole arrangement. They actually sound just as good as any other pair of shiny plates I've got, so I kept them. 

Example 3: I also like the fabled Tung Sol round plate black glass 6SN7, but it's hard to find tubes that are strong. The heaters on these also commonly die (even if they tested good). So I've ended up now with a pair in my amp where one has the oval-mica construction and the other has round mica. Sounds great, no problems!

Mac new branded tubes are JJ’s. Not the best but reliable and available.