Calling All Tube Gurus

Here is a paragraph from Joe's Tube Lore. See if this is helpful information. For details, check the link.

Be careful of getting hung up on the brand name printed on the tube. In my experience most Siemens 6DJ8 family tubes you will find in the US are labeled anything but Siemens. Why? Siemens (and most other manufacturers) served as an OEM (original equipment manufacturer) supplying their tubes to many other tube manufacturers. While Siemens made these tubes they were labeled with the name of the company they were supplied to RCA or Phillips for example. Now not all RCAs and Phillips were supplied by Siemens, so that’s where points 1 5 on how to check tubes comes into play. Fortunately, in many cases the tubes are labeled with the county of origin & that can help you identify a tube’s manufacturer. Made in West Germany? It’s usually a Siemens. Made in Holland? Probably an Amperex. Made in the USA? Usually a Sylvania or an Amperex. Oh yeah a useful tip: RCA never made 6DJ8 family tubes. If it’s an RCA and has a ridged top it’s either an Amperex or a Siemens. I’d watch this brand closely if you stumble on it. Many tube dealers will sell lowly RCA 6DJ8 family tubes for $15 to $20 a tube without realizing that there is European made gold inside. Check the tube’s top for ridges, the label for where it was manufactured and if everything checks out, buy it! This is one of the absolute bargain brands in this tube type.

Amperexes were also frequently OEM’d to a variety of manufacturers. Most commonly to Mullard, DuMont, Beckman, Hewlett Packard and a few others. The risk with Amperexes is that they do vary by vintage and model and it’s hard enough to keep that straight among Amperex labeled tubes. Which vintage / version are you buying under another manufacturers brand? Who knows? It’s just pot luck.

https://www.audioasylum.com/scripts/d.pl?audio/faq/joes-tubes.html

Anybody know who makes McIntosh branded tubes?

To your date code question: I think it's not really relevant as tubes from the same batch can vary by a LOT.  I read that manufacturers think 5% variance is fine. Try 5% louder in your left channel and me that me 5% is fine. :)

I once replaced a pair of Sovtek 6550s that were damaged by red plating. I bought NOS Sovteks that were matched. Popped them in and viola! Louder on the left. Another tube- a Sylvania BH7A was causing the red plating. I replaced it with NOS. Soon after the right channel BH7A started acting up.  I realized that the best practices way to have avoided all this wasted time and money was to buy a whole tube set already matched from my manufacturer. "Your first loss is your least loss" 

I don’t mean to derail this in any way but wanted to add my experience. In the pursuit of better sound we search out tubes,sometimes based on some thing we read like "Joe’s tube lore".Why Not ? It’s a fun and informative read. But these and similar reviews/comparisons, although meticulously done, might only have used a single example of a given tube. Someone like Joe, came to these conclusions within the context of his system, preferences, and gear that  was posted on the asylum 25 year ago. Much has changed since then including equipment and tube supply.

Tubes can vary, time and usage takes it’s toll if the tube is not New Old Stock. I trust the opinions of the best tube resellers like Brent Jesse. They have experience with multiple examples of a given tube over time and have a reputation/business to maintain..

One can generalize that performance will be similar over many years of a tube’s run if the internals look the same and that may be more important than getting stuck on a specific date.

I’ve bought supposed "Holy Grail" tubes that have "underperformed" my expectations.

I’ve bought tubes that are not the same date codes as the recommended ones that sound as good because they are the identical construction. Buying old tubes is a bit of mine field but So worth it when you do find the gems.

Case in point I recently bought some Matsushita tubes.When Mullard closed down Matsushitu bought the tooling from them and continued to make them in the meticulous way the Japanese do. The resulting tube is sonically equal to the equivalent Mullards I have and were a fraction of the price and easy to find New Old Stock

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.