This a about a TERRIBLE and really disgusting way to FAKE the extremely expensive TELEFUNKEN ECC802S
Some information about ECC82, ECC802S, 6211
First, a small information about the right type of tube to use. Really some electronics designers think they can create "better" design just by doing things "different". But when I see this develop into a discussion about design problems vs. tube problems, it becomes a waste of time. Most problems result from choosing tubes for an application which they were not intended for. It results from doing things different. People see a particular tube (optically) and want to use it in a circuit, without reading the text part of the data sheet, writing what the tube intended for. Then we see driver tubes in a phone stage, or switching tubes (like 6211) as a audio tubes.
Of course we take it for granted when tubes for small signal are less microphonic. Yet accepting the other side if this story is generally a problem. So people simply use tubes intended for large signal in a pre amplifier, and any noise problems from this are called "tube problems". They feel justified, because they can prove the brand differences. The tubes are simply divided into such that are bad and noisy "by the brand" and some that are not, and the thinking ends at this level. Then, when explained how to use (what they regard) noisy tubes in the right circuit, and they are not noisy at all, they say this a silly excuse for the noise problems.
Another such a problem can result from taking tubes which are intended for small signal, and use them for high signal. Small signal tubes are by nature high gain of course. What else do you expect. However high gain tubes, have a higher output impedance than low gain tubes. The gain is coming at the cost of the negative properties that come along with it. Only with clear understanding of the intended use of products (not just tubes), a reliable product can result from it.
In this context we have to place the ECC82. This is by nature a general purpose tube. So it has reasonable low output impedance, at reasonable gain, and reasonable undistorted curves. This tube was very popular, because of the data is quite "general purpose". Some call it a tube of the kind: What goes in, is what comes out.
However, to get the low impedance, and to get the low distortion, there is a drawback, and that is you need high anode current. And the drawback from this is lower lifetime.
In this picture we have to place the SQ tubes, five star tubes, 6189WA, and from Telefunken the ECC8xx-S series. So I begin to speak again about the intended use. These Special Quality tubes are intended for the things they are intended FOR, and you need to read that in their data sheets, not in tube babble forums. Data sheets are really very clear on that.
Now comes ECC802S. What do we read in the datasheet? Well many, very many things are written there, which will fail in the ECC82 datasheet. This by itself describes the weakness of ECC82! So when you are interested what is less good about Telefunken ECC82, read in the Telefunken ECC802S datasheet what is improved. It is really that simple. The same way for Sylvania 12AU7 vs Sylvania 6198WA. That compare will unveil other information as Telefunken ECC802S vs Telefunken ECC82.
So we stay with ECC802S now. Mainly, this tube is described as "Long Life" 10.000 hours, and plate current of System 1 and System 2 is balanced, and min-max windows are specified, and it is low noise. The published improvements are the largest with Telefunken, and improved tubes USA brands do not match this high standard. This explains the popularity of the ECC802S
How was this achieved? The longer lifetime results from larger anodes, which reduces the temperature. Also TFK uses a special cathode coating. In the end, tighter specifications result from smaller manufacturing tolerance (on anode distance), longer burn in, and of course checking mire parameters, and check those more critical. The latter is called "uptesting".
We have to say it, ECC802S is the finest ECC82 ever made, but unfortunately the market was small for such an expensive tube, and production was always low. There are simply not many around, and a good pair cost around 500 Euro (price of 2019).
The TELEFUNKEN ECC802S.
There is another dedicated tube which is the 6211 switching tube. Switching tubes are really intended for on/off situations. So high output current, such as relays need, combined with high transconductance and high gain. How is that magic possible? Well very simple: Linearity is terrible, which doesn't matter for the application. Yet, when looking at the curves, they are not so terrible, as long as you work at low voltage. However at 250 or 350V as you can do with ECC802S, the tube is not good for HiFi..
Telefunken made their 6211 from the ECC802S parts, because they already had those, but used a grid with half the wire distance. Also increase the anode distance a lot. This makes it a totally different tube, with twice the transconductance, and twice the gain of ECC802S.
Yet in several auto bias circuits, the tube appears to work, though plate current will be only 60%. Only, it works not very good, because high signal will come at the cost of too much distortion.
It should be clear, the FAKING MAFIA will re brand the TFK 6211 as ECC802S, and end users have only small chance to find it out. However, today's mobile phone cameras are now so good, you can use them as a magnification tool.
How to recognize fake ECC802S made from 6211.
1) By electrical testing
At fixed grid voltage, they test like "just ok" ECC802S. So a bit low on anode current. However if they were really weak indeed, just go to 10% over heating, and they would become a lot better. Doing so with 6211 will give no change. This is proof the 6211 is at least not poor in emission, and then it is also proof this is a faked ECC802.
2) By electrical testing
This is very confusing, and Gm will be "excellent" when you use non-numeric testers like TV7. Moreover you would use bias for 12AU7 of course, but that will reduce plate current, and consequently reduce Gm too. So the tube will test "excellent" still but not crazy high. But now try it with 6211. And you will see it is no more than a good 6211.
When you use testers with real parametric testing, you should set the plate current to values which are normal for ECC802S. (Since you have a 6211 on the tester) Now the truth will unveil quickly, Gm is 6000 instead of 2000 for ECC802S. So a CRAZY difference.
3) By electrical testing
Few testers can do this, but if you can you will find gain is 40x instead of 20x.
So electrically it is a total fraud.
4) Visually. This text here applies for TELEFUNKEN only.
You can see the grid though the little inspection holes in the anode. The grid of real ECC802S will show 3 grid wires. s.
The grid of 6211 will show 6...7 very fine grid wires.
Here are some pictures I made of faked ECC802S with a low cost mobile phone. ( I used an Iphone 5c)
I bought these from a large and very well known tube dealer in Germany. I can not write his name here of course.
Original Telefunken ECC802S, showing three grid wires through the inspection holes.
Faked Telefunken ECC802S (re branded Telefunken 6211), showing seven grid wires through the inspection holes.
CAREFUL: This grid bar color may NOT have to say very much. You should not use it to determine spot a fake, because I have seen also (real) 6211 with white grid bars. It is at least something to keep an eye on. What really counts is the grid wire distance as in the previous pictures.
5) The data code. Fakes have typical always the same date code. With originals when buying RARE tubes (and ECC802S certainly is) you can call yourself very lucky when two date codes are the same. But here, from 10 tubes, 10 had the same date code.
Moreover the date code originally is printed vertical as a SEPARATE printing. Just imagine a production environment. Logically, the data code. stamp is made by it's own tool, with a date clock in it. Perhaps even stamped by hand, and print quality can be lower, so we talk about a tool here. Not about a special logo stamp. Whereas Telefunken brand logo is stamped with a very high quality tool, which gets made and then used for many tubes. That can never include a date code of course. .
With the fakes, the date code is part of the branding print.
7) Plate distance. Not only they used another grid for the 6211, also the plate distance is wider. I did not want o break tube glass, just to see that, but I would estimate with ECC802S it is a little below 3mm, and with 6211 it 4.5mm. A bit difficult to see when looking at only one tube, but very easy in direct compare.
Increasing plate distance will increase the gain because there is now less anode field feedback to the grid field. (fields add up, but anode field is 180° phase shifted). Also this generally stretches the vertical axis and compresses the horizontal axis.
6) The individual number. This is the small printing on the TOP of which I do not fully know it's function. These 3-digit numbers seemed randomly, on the 10 tubes I received.
CALL FOR HELP: If somebody knows more about these numbers, please let me know!
7) The boxes. It hard to fake old boxes.
8) The tube curves.
This is from the faked ECC802S.
I made the curves myself, with my SOFIA Tester, using some pairs of FAKED ECC802S, I recently bought from a well known, large German tube dealer. It is clearly visible from the curves, these are 6211. It was no problem to give them back, but I can tell you when you only use a parametric tester, like the AT1000, or every other tube tester, and set it for ECC82, these tubes will test 'good'. It went like this: The first tube was "just ok". Well it can happen. The second tube was "just ok". Well, bad luck. And the third tube, and the fourth... etc. So I just made the tube curves, to see if there is some general problem with the emission. But the emission was good. Only.... what weird curves, totally unlinear. It took me quite some time, to realize I was fooled, because I never heard of this faking method. Then when I compared the curves with 6211, it was a hit. Yes, these are 6211, they rubbed off the 6211, and printed ECC802S on it.
The strange shape of the 0V curve is typical, and of course the bias point at 250V 10.5mA is totally wrong.
These are the faked tubes. These are 6211, not ECC802S.
Date code: U1006203 d