"tube tester to check gain and fidelity"

I'm afraid it's impossible. Both gain and "fidelity" (linear and harmonic distortion, cross-modulation) depends on the whole circuitry. You can test for example the emission.

Thanks for your good answer. Yes I handle my collection very carefully if they are vintage or new. Some print will just not come off like Raytheon "England" which are Russian fakes 6L6GC pre-1980's. The Yellow print is excellent looks like thick paint. To bad they are fakes. This is well documented on the Web and I got them free early 1980's and I have sold (6) of them so far and of course I told them they are Russian fakes not "Made in Great Britain" but they have the best print I have seen and they are old new stock or NOS tubes!

If they are using strippable paint = cheaply made. They used to etch the details in with a water based paste with some fluoride that was then washed off = permanent.

Yes I believe you are on the right track the print does look cheap when it looks as someone has rubbed of the print also by a bad manufacturing process or by handling the tube. Telefunken tubes which are considered by some as the best made and sounding tubes in the world are famous for there print to be very bad or completely wiped off due to age and handling. Yet people will spent $150-$250 for a "quad" (4 12AX7/ECC83 tubes). I bought a quad with very good print 1960's vintage for $177.50 total a great deal! They are great tubes and have a diamond glass logo at the base of the tube between the pins which tells you they are the real thing from W. Germany. There are fakes out there! But for new tubes to have bad print this is strange. Tube buyers are extremely picky and bad print is not desired. Thanks for staying on topic and for your good answer.

The ink you are referring to is a chalky, off-white type that was started to be used in the 60's, it will literally fall off the tube, even sitting in its box on a shelf. It decomposes in a relatively short time and unfortunately, it became a very common ink in the industry. There is nothing you can do about it, it will fall off no matter what.

Modern tubes could be using epoxy ink to print their tubes but they aren't, they are using cheaper ink which will come off almost as easily as the defective 'chalky' ink. We are talking pennies per tube here in cost difference for inks but try to tell that to the pencil-necks running the show. Cost cutting is the name of the game.

Fortunately, most quality made tubes had genuine date codes printed (or scribed) on the tube with the better ink making it much easier to identify 'real' NOS tubes. Unfortunately, the counterfeiters can duplicate the diamond in the glass as well as fake codes, however, the quality is almost always a giveaway. The glass will have flaws, the diamond poorly executed and the fake manufacturing codes don't make sense. When buying tubes, you must depend on the dealer's knowledge and honesty (in some cases) to sort out the bad from the good or a dealer who is willing to take back the tubes if you don't like them.

I bought Mullard tubes several years ago on e-Bay, in Mullard boxes with the correct chevron on it. Turned out they were 'fakes' , I knew they were of Russian origin, by their construction, an equivalent tube common in Russia and on the tube markets, on examination. Since they cost me next to nothing, I didn't make a fuss except to contact the seller and let him know about it.

Complicating things to some degree, many old tube brands have been bought (legally) and current production tubes are produced with the genuine logos, the fly in the ointment is that these tubes are not the equals of the original NOS unfortunately despite claims to the contrary. NST (new stock tubes) may be 'genuine' in print but they are rarely, if ever, the equal of the originals. A logo by itself does not make a tube a good tube.

While print quality may be an indication of tube quality today, it doesn't apply to the original NOS tubes with lousy ink. My inclination is that somebody decided to try a new, less expensive ink, which passed muster at first, then when the ink started to decompose in the field, it was getting too late in the game to change back to the original inks as tubes were alreay in decline. As you noted, Telefunken was a very good example of this, the tube was still great but the ink stunk.

Personally, I am much more interested in the fact that a tube is genuine, the print has no function other than to identify and a partial logo or manufacturing codes can still identify the tube as genuine. A collector may want 'perfect' tubes which is perfectly fine if that is what he is collecting, but it has nothing to do with the operation of the tube. It will still work the same with or without printing on it.

Thanks for that great answer the best to date. I have found on eBay for example first tube people buy the great sounding tubes Telefunken, Mullard, and also USA brands NOS. Then if you look at the picture of the tubes the highest bids seem to go to tubes that have good print in good condition and good test results. I actually saw pictures of an estate sale NOS brand new NIB Telefunken with perfect print it was incredible. I did not even bother to bid on them knowing they would sell for hundreds of dollars. A used quad will go for $250 easy. I bought a quad for $177.50 with very good off white print as you said and (2) Amperex Bugle Boys both were 1960's for about $65. They not only function but if you have extras that are not so good as far as looks and test results I sell them at a profit. The only new tube I like and have used are JJ Telsa from Slovakia used to be commie Chech. I am using them in my amp now (2) 6L6GC matched perfect and they sound great and the print is Red and perfect (I don't get it EW they are not commies anymore). That Chech. country that Russia took over split in half Chech Republic and Slovakia after the Russians split. But I like JJ tubes so far with the best print I have ever seen. I will try to post a picture of great print on a new tube and 1960's used tubes with off white print in very good shape. The red 12AX7 JJ Telsa and a picture of a quad of the Telefunken 1960's.

Amperex is one of the brands that has been bought and is very often paraded out as the 'genuine' item....sorry but only the name is genuine, the tubes are only shadows of the past. It takes more than just some of the original equipment to make good tubes, testing racks don't make the tubes! Tung-Sol is another brand bought out and paraded around....same thing....the tubes aren't that bad, they just aren't the genuine article!

Frankly, I think the price of many tubes are just plain ridiculous! First off, if there was such a shortage, how come there is a relatively constant supply of them coming into the market? Just enough to keep the prices up.

Actually, the Russians can be very good at making tubes, believe it or not, maybe not quite the same as Telefunken, RCA or Sylvania and others, but they CAN be very good quality. The problem is that there are also not so good tubes out there and it is very difficult to tell one from the other. The Chinese are another similar case, both the Russians and Chinese can produce really good tubes but very often, the Chinese in particular, quality control is problematic. I've seen a very good batch of tubes with very few rejects and the very next batch is just full of rejects. The only solution is to test 100% which is not a very good option.

I've had very good tubes from Tesla too but also not so good tubes.

One very big problem with making a quality 12AX7 is the physical problems involved in making it. It is small to begin with, the grid is wound with one of the finest gauge wires used in tubes, the control grid is very close to the cathode and very slight variances in winding the grid or making, and welding, the elements in place causes large variations in performance. It is a very problematic tube to make and contrary to general thinking, even Telefunken had a fair sized reject pile despite a really good production line. They were just a little more fussy about what tubes got shipped from the factory perhaps.

I've recovered very few Telefunkens, even right out of a unopened box, with print intact from the 'chalk' era. Back in the good old days, we weren't fussing about the print on a tube at all, it was of no concern. Besides, there were American tube brands that were buying batches of tubes from Telefunken and printing their own logos on them, it really was a very common thing back then for one 'brand' to buy tubes from another 'brand' and label them with their own logos. They all did it to one degree or another. That coveted black plate RCA may have been made by Sylvania and it wasn't always easy to tell.

You know I think you are right on!!! Your last 2 articles talked about print being a manufacturing problem and age also NIB even. My question has been completely answered mainly by you but a couple of others on this thread and I thank you all very much. I love it when Engineers come up with answers based on knowledge and experience.

I was thinking the same exact thing about Telefunken being hard to find and then I looked at the market and there were so many Tele tubes out there I could not believe it! And people will pay lots of money for them including me. Though I am biased (forgive the pun) since many years ago I listened to a real Telefunken radio from the 1950's I believe and my Mom still has it. It had SW and the reception was amazing using a built in antenna.

Russian fakes is another story. I just sold a quad of Raytheon 6L6GCs labeled "England" which if you read the web about these tubes why not say IN RED "USSR" the print is yellow and these tubes are pre-1980 NOS when I got them free from Water & Power. Though I was very honest in my ad that these are NOT English tubes which everyone seems to love and told people in my ad if you like Vintage Russian tubes here they are and they are fake. Since you spoke about fake tubes also I want to help educate everyone and show this picture of genuine fake Russian tubes manufactured pre-1980's and people still want to buy them!