Creating UTS Files (Example: 12AT7)

[Rocko]

First off I am really sorry about posting again. 

I looked at the 12AU7 spec sheet and well that was easy, the numbers and wording is clearly laid out to enter the correct values to save a UTS file for testing all 12AU7 tubes, yeah!  This applies to all software really saving tube data for later use.

But, when you get to the 12AT7, how am I supposed to know that you enter -2 for Vg?

https://frank.pocnet.net/sheets/093/1/12AT7.pdf

I there a tried and true way of figuring this stuff out?

Thanks in advance,

Rocko

[Martin Manning]

Top of page 2, 250V Va. That's always Va-K. You can read there the amplification factor µ = 60, plate resistance ra = 10,900Ω, and transconductance gm = 5500 µ-mho (that's 5.5 µS). Plate current is 10 mA. It doesn't give a grid voltage there, but if you find that point on the plate curves (top of page 3) it's -2V. 

[Martin Manning]

Oops, sorry, 5500 µ-mho is 5.5 mS.

[Rocko]

Martin,

Thank you very much.

So just so I am clear for a 12AV7 I would do the same thing and this is what I would enter for a quick test as an example?

https://frank.pocnet.net/sheets/093/1/12AV7.pdf

So everyone of the 1987 users of Utracer3 world wide has had to do this and create hundreds of UTS files for all the different tubes?

Rocko

[Ihor]

No, those files/measurements are already created by all possible tubes by the manufacturers, those are plots in datasheets :) Those 1987 users just do test to see how their specific examples differ from the expected average claimed by the manufacturer. 

In reality, you can test any point on the curve to see how good your tube is, and most of the time it is done at the Operation point of your amplifier, or where you want to get matching and so on. You can always go the the description of Class A amplifier in any datasheet and pick up Va Vg and Ia from there :)

[Martin Manning]

That looks fine to me. Those two are older data sheets. Most will have a 250V operating point with all of the parameters listed. It really takes no time at all to accumulate .uts files for the tube types you normally encounter.

[Rocko]

Martin/Ihor,

Thank you for the clarification, when I looked at the graph to find the -1 for the 12AV7 I figured that I could pick any of the intersecting points and test to see how it would perform and create my own test if I wanted.

I did decide to build the Utracer3+ because I wanted to learn a little more about tubes.  I have 1000's of them and want to be able to check what their state of operation is. 

In addition, when I purchase tubes I wanted to be able to verify I was getting what I was supposed to get.  Unfortunately, so far my brand new tubes test like garbage and my NOS tubes test darn fine to the "Characteristics and Typical Operation" sections on the tube data sheets.

Here are 2 brand new tubes (maybe I am doing something wrong?):

Brand New Gold Lion Genalex 12AU7:      

https://www.tubeampdoctor.com/en/gold-lion-12au7/ecc82-genalex/russia?c=177

Brand New TAD Highgrade 7025:  

https://www.tubeampdoctor.com/en/7025-highgrade-tad-premium-selected?c=138

I still need to figure out what tracing parameters I want to have for each tube and save that in the setup file for each tube as well.  

The idea of it only takes a few minutes to enter this information for each tube may be true for someone who reads university physics textbooks for fun, but for a fat old drunk who likes to listen to music and is a tube enthusiast, I hope I have not bitten off more than I can chew or I run out of life before I get them completed, lol.  Maybe the 3k on an Amplitrex would have been the smart thing.........

Time for a glass of vino, :).

[Martin Manning]

>>>>I did decide to build the Utracer3+ because I wanted to learn a little more about tubes. 

Mission accomplished.

>>>>I wanted to be able to verify I was getting what I was supposed to get.  Unfortunately, so far my brand new tubes test like garbage and my NOS tubes test darn fine... Here are 2 brand new tubes (maybe I am doing something wrong?):

Doesn't look like it. You'll get slightly better numbers if you tweak the set voltages up so the measured test voltage hits closer to the target (you're a couple of volts low there). Ihor's uTracerJS has a built-in iteration that does that, which is nice. Tube quality isn't up to what it was when they were current technology. Most sellers don't specify tolerances when they advertise "select" or "matched sections," but that 7025 is definitely send-it-back bad. Note the TAD write up has no numbers quoted for what they deem to be premium quality.