For Tube Folks...

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

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.  

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.

@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.

Does it matter really, strictly NOS or not quite ?

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.

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.

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.

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

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.   

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.

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

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

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

@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.

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.

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.

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.

Hi All -

I really appreciate the information. 

A special thanks to @ Viridian for mention the "The straight glass, three getter tube has a side getter so will have silvering on the side in addition to on the top"

I do not want to delve into the what constitutes 'NEW' or 'USED' conversation at this time, but that may be a worthwhile string someday...

My question -  Within reasonable certainty, is this tube is NOS or is it USED?  

@inagroove Just look at the pins of the tubes. If you see scrapes along them the tube has been inserted into sockets a few times. An NOS tube will have no scrapes.

The pic you show has a very large side-getter patch (good), with light-gray fringes that indicate some light use - roughly consistent with the seller’s description. As use continues, the side patch typically shrinks (well before the top patches), with the fringing sometimes becoming more dominant. I have some GE 7581A with chrome side patches and NO fringing, that are probaly truly NOS. Anyways, to see a very large side getter patch on a power tube (dark metallic or chrome, NOT chalky white/gray or brown) is usually a good sign. (note: if you see a side patch on a tube that shouldn’t have a side getter, like an EL34, that’s bad news lol)

The debate on "NOS" nomenclature is boring semantics. NO I wouldn’t call this tube strictly NOS, but these days very few tubes left are. If the seller’s description is accurate, and seller can be trusted, I’d be happy with ’em.

+1 atmasphere

I examined the pins when I cleaned them.  All showed light-ware - a sheen that indicated they were inserted into a socket.  I was not alarmed because the seller's description indicated that they had been tested and had some burn-in hours.  Perhaps I should have thought twice...  

"An excellent lot, matched to within 5 percent and then aged in a hi-fi shop demo unit. Very low hours, burn-in time only, and the performance has been verified by us..."

Regards,

+1 mulveling

Thanks for the details regarding the side-getter patch-chronology - very helpful.

As a novice, this is my first tube with a side-getter as well as my first 'NOS' tube purchase.  If I purchase another, I will be better informed...

Regards,

NOS   New Old Stock, usually from old inventory from out of business retailers. Boxes can show significant shelf wear.

Even new tubes are tested by resellers before they're sold. A while back, I bought four Telefunken military grade tubes for a radio multiplex. I got them on eBay and the seller was, I believe, an old Ham Radio Operator and these were from his own collection. He had an Amplitrex tester and was very transparent about the whole process. I just had to make the decision on whether or not to trust him and now, I'm really glad I did. But this was long ago, way before the insane prices that we now see for NOS Telefunkens. 

Currently I'm in the market for a Linlai E 6sn7. I've decided that there are some new tube manufacturers that offer a better value than those highly coveted Western Electric, etc... Plus when you by a new tube, it comes with a warranty.

Use the new tube, it's the way to go. You are trouble free.Tung Sol is good enough for me and it's lifespan is very long.

@ghdprentice   once I went to your pictures - it appears you are quite the photographer. Thoroughly enjoyed some of your city shots after the tubes.

You know how to make a camera sing !

@firberger 

Thank you.

If you want really well matched output tubes you need to burn them in for awhile and retest. They will drift around a bit when they are new. Unless you are curve tracing, you will need to test under the conditions of your amp. Fixed bias amps usually allow for adjusting the balance of the bias current in the output transformer so perfect match is then not necessary. With cathode bias you will want to be closer. If a tube is going to fail from a defect, it will most likely fail in the first 100 hours. Also, in my experience it takes tubes 50-100 hours before they sound the best. For me it doesn't make sense trying to locate matched NOS output tubes. I would suggest finding current production output tubes that you like and stock up. And if the dealer burns them in first before testing I would consider that a good thing.

As for boxes, tubes from the 1950's & 60's the boxes used cardboard with a high acid residue that over time turns them a brownish color and makes the cardboard very brittle. Just opening the box to test can damage the packaging.  

I still own a quad of matched GE 6550’s. I have them because they are a superb sounding tube and quite robust. I removed them from a Melos tube amp that I bought new and that used these as the power tubes. Replaced them after just a few hours use with a quad of KT88’s, which gave me a little more power.

If the GE 6550’s that you bought work well in your system, then you have some of the best power tubes out there. I went through a number of tube amps in the interim years, some with Winged C 6550’s, still have the GE’s to this day..if that tells you something.

If you want really well matched output tubes you need to burn them in for awhile and retest. They will drift around a bit when they are new.

Referring to what @john_tracy typed above, the second time I retubed my V12 I went with a couple of sextets of EL34s that Jim McShane sold me.  It took a while to get them, and every couple of days he would send me an email telling me how the matching was going.   I think that was sometime in '20.  I set the bias and for the longest time it stayed where I set it on both sides.  

On the other hand, the first time I retubed that amp in 2018, I bought two sex tets from Viva and they arrived quite quickly.  So I don't know if they keep a lot of tubes properly burned in and matched, or if they don't put the time into matching them that Jim did.  I do remember the biases doing some goofy things with that batch of tubes.  

@runwell Keep the new tube manufacturers in business because at some point in time, NOS will no longer exist. Some well reviewed newer tube brands out there; Grant Fidelity Special Edition, Linlai Elite, Apos Ray Reserve.

@daveyf

Thanks for your encouragement regarding the quality of the 6550 power tube. I appreciate hearing of your first-hand experiences.

@goofyfoot

Thanks for the names of the 'newer tube brands'. I have not heard of them.. I hope they prosper... but not too much ;-)

Actually test data is very important but doesnt tell you if the tubes are lightly used or not. It is not unusual for there to be up to a 15 to 20% difference in the test readings on NOS tubes of the same type and manufacturer. So you can actually have lightly used tubes which can test higher than true NOS. 

As Ralph points out, the tube pins are probably the best indicator of use. However, if the tubes were tested then there can be vertical marks on the pins. Heat marks/discoloration can also be an indication of use. Problem is that the process of manufacture wasnt exactly as we expect today and variations on things like getter flash, clearness of glass, etc are not uncommon.