For Tube Folks...

As a side note, watch out for eBay sellers who offer "NIB" (new-in-box) or "NOS" tubes in "original" boxes.  Some of theose boxes are reprinted stock white tube boxes.  You can usually tell when you see white edges outside the original labelling.  Another tell is identical coding on the inside flaps of the box, indicating there were printed from an image of a single box.

Since we are talking tubes, does anyone know how long 12AU7 RCA blackplates from 50s usually last ? I don’t mean military/industrial Command blackplates. What about 12AX7 Mullard longplates? I understand it may depend on particular amp.

That’s what I use, close to 2000 hours on them.

Never had a single failure with Svetlana, SED, SED Black Sabre  EL34 in decades running in CJ, Cary, Latino Dynaco, Prima Luna amps, tese all 90's production tubes. Always heard quality went down in later years.

Ran some GE 6550's in Cary amp, did not like those, all muscle no finesse, EL 34 has always been my fav for push pull amps.

Respectfully disagree about the "O",  as I have heard it both ways, and whatever your definition, the "N" certainly stands for "new".

The point about burn in seems an excellent one. But to me, it would apply more to current production new tubes, as opposed to new original tubes. My experience, a sample of one, is that current production tubes lack the reliability of vintage tubes and have, generally not been previously used, as they are often purchased from dealers. So burn in seems a very good thing in this instance, and the provenance of new production tubes is, rarely, in question.

That is my experience in 50 years of collecting, but could certainly be insufficient experience and definitely I am an insufficient sample. Much of this stuff is anecdotal, IMHO, and YMMV. I can certainly see other ways of looking at this one, and respect other points of view.

@viridian you statement ‘The "O" in NOS stands for original, as in unused, the way they came off of the assembly line. Once the tube has been powered up in anything other than a tube tester it is no longer NOS.‘ is incorrect  

The “O” does not stand for “Original” but for Old.  “NOS” stands for New Old Stock.

I do agree that if a tube is burned in or particularly aged,” it’s no longer a NOS.

Having said that, I think it is worth keeping in mind that, for example, if you buy a new manufactured tube, say a KT120 at Upscale or even Audio Research, they do burn them in for 48-72 hours and they’re still selling them as new.

So I think being burned in is a more of a gray zone, but they certainly have been burned in on a burn rack for a very prescribed time rather than in actual equipment.

NOS is like virginity, it's either untouched or it isn't. There is no in between.

'NOS' stands for 'New Old Stock', not 'New Original Stock'. 

Those SEDs hold the bias well. I mean, the working ones.

I hear you Inna. I am fond of the most disliked tubes, JJ! And while the anecdotal evidence is mixed, many have had failures. I have had over 30, output and small signals. No failures...yet, however the bias on some of the output tubes is squirrely.

It’s very unfortunate that these modern tubes, made in the far East, and Eastern Europe, from the large manufacturers , don’t have the reliability of old tubes. It’s a bit of Russian roulette, as you unfortunately found. But like Matthew, I don’t really care for the sound of the Tung-sol coke bottle tubes, or the GE straight bottles, and as pointed out, the prices have been usurious for decades.

viridian, alright, I got you.

In any case, I don't enjoy throwing out $120 tube after a few months.

I have modest resources and can't afford $300-$450 a piece NOS Mullards. Tube Depot sells them with 90 days warranty.

Wouldn’t that be "...not very reliable tube..." not, ..."not very reliable tubes..."? Yes, language matters.

In the '90s I had a couple of amps that used 6550s and I remember Cary was putting them out with and selling replacement Svetlantas (first the Bs and then Cs).  I bought eight Tung Sol 6550s that were theoretically NOS from Andy in Michigan and they cost what I considered back than to be  an arm an a leg, but they really didn't do anything that I thought was way better than the Svetlantas that I had been using.   

Right. Just as I wouldn't buy unplayed record for any significant amount.

What is the definition of nos? If it means a tube that is sealed in the factory box, I wouldn't want to buy it without it being tested. If it means tests nos, I would still have to know the seller or at least their reputation.

Currently using a quad of SED winged "C" EL34 in my VAC. One was gone after 700 hours, had a spare. Bought them from Tube Depot. Not very reliable tubes, I guess, or it was just a bad luck.

Those are Russian 6550, no side getters, they are designed with top getters only. I remember the good old days when ARC used the SED winged "C" 6550s. Long gone now, glad I squirreled away a few quads.

And Inna, yes language, and terminology, matters, IMHO and YMMV.

Here are photos of new, burned in and tested 6550SE from Audio Research,

https://www.flickr.com/photos/jdflood/54304855877/in/dateposted-public/

https://www.flickr.com/photos/jdflood/54305962264/in/dateposted-public/

No blackened areas.

Does it matter really, strictly NOS or not quite ?

Looks like silvering on the side getter, should be a usable tube.

But no, not NOS, the seller admits to that in the original ad when he says, "aged in a demo unit.." 

@carlsbad2 has it correct. The only way NOS status can be trusted is if the seller purchased the tubes new directly from the manufacturer AND you trust the seller is telling the truth, as it's unlikely they have the invoice from the manufacturer to prove it. The most that can be said about any tube is that it "tests as new" and even then only on a recently calibrated tester and from a trusted vendor.

As for myself, I'll only buy recently tested tubes from sellers with good reputations, and even then I'll test them before I use them both to verify their test data and to make sure they didn't get damaged in shipping. Or I buy cheap lots of untested tubes and weed out the bad ones. I'm found some gems that way.

Thanks to all.  I appreciate the information!  

Also, I have failed, twice, to post a photo of the tube on this thread.  

As a work-around, I added the photo to my SYSTEM, for clarity.

NOS is an overused term.  Sellers call anything with a box "NOS" and buyers ignore the obvious exaggeration.  I've even seen tubes without a box called NOS. 

 The key is test data.  

Of course, there are different GE branded 6550 tubes. The straight glass, three getter tube has a side getter so will have silvering on the side in addition to on the top. The ST shaped GE tubes are just rebranded Tung-Sol coke bottles.

BTW, if the tubes have been used, broken in, or "aged" (what a laugh), they cannot be, by definition, NOS. The "O" in NOS stands for original, as in unused, the way they came off of the assembly line. Once the tube has been powered up in anything other than a tube tester it is no longer NOS. Just another used tube.

The black part on the side of a 6550 is part of the manufacturing process and is there from day one.