µTracer Build Questions

[dorrisant]

When running through the build, (came out fine) there were a couple of things I found odd:

Referring to page 41 and a little after, I got a measurement of 69v at the 50v interval even when the 200v was calibrated to within .5v. The same thing happened on the anode and screen supplies. Both showed measurements of +15 to +18 over the steps of 150v to 300v. Still showed 69v where I should see approximately 50v. I went forward with the con manual, thinking that it would be covered later. It never did. Is this just tuning the scale at 200v?

The other thing is on page 45, step 43 calls for a measurement of 10mA. I believe this should be 20mA. Please correct me if I'm wrong.

Going through the user manual now. Will test with it very soon. Concurrently I'm planning the details of the enclosure. All fun!! ...and more questions.

[martin manning]

When you are measuring from ground to the anode or screen you will see a voltage that is higher by the amount of the supply voltage (~19V) because the cathode terminal is sitting at Vsupply. For that test the manual tells you to look for a voltage that is set point voltage plus Vsupply.

On the current cal, it asks you to verify that the current and voltage are consistent with a 10k resistor, i.e. V from the plot divided by 10, with the answer in mA. The 10 is 10k ohms.

[dorrisant]

Thanks Martin! That is what I needed... to read a little deeper and then do the full cal. All is great now!!

Just traced a burned-in matched pair of JJ EL84s from CED. Not too bad at all.

[martin manning]

Nice! You can clearly see that testing at a single point does not tell the whole story ;^)

[dorrisant]

Where is the information for the connection of a twin triode for quick test? I see the connections for the plates using the plate and screen connection for the plates and I assume the grids get tied together for this test, but where exactly does the second cathode get connected? I do not see this in the manual anywhere.

In my opinion, this should be clearly explained in the user manual. I don't see it anywhere. This is very disappointing... I have time to try this out but have to wait (for who knows how long) an answer that doesn't seem to exist in the manual or on the internet.

I did find this: http://tronola.com/html/tube_analyzer_y ... page2.html

"I also used the Supp (Suppressor) “source” to connect the second cathode. So the full connection list for the 12AX7 is:

Source Pin Comment
Htr 4
HtrG 5
Cath 3
Supp 8 for the second cathode
Grid 2
Scrn 6 for the second plate
Plate 1
Pin-2 7 banana cable jumper for the second grid"

This does not help at all.

[martin manning]

Both cathodes are connected to the uTracer's cathode terminal.

[dorrisant]

Both cathodes are connected to the uTracer's cathode terminal.

Is that in the manual? If so, where?

[martin manning]

Both cathodes are connected to the uTracer's cathode terminal.

Is that in the manual? If so, where?

Apparently it's not, but how else would it go? ;^) The same applies if you are tracing curves. It would be better to avoid any confusion and write it like this:

"The triode Quick Test has been designed so that both sections in double-triodes are tested simultaneously (Fig. 5.2.2). In this case the anode of the second section is connected to the screen terminal of the uTracer, and the grids and cathodes are connected as if the two triodes have been paralleled."

[dorrisant]

On the quick test... what value is entered in the field indicated by the red oval? When I enter the Amplification Factor here for 12AX7s all is fine and the percentages are as expected. When I have tried to set up power tubes, I entered this number (AF) and get wildly high percentages. Is there a way to derive what this number should be from the datasheet? I can't find anything by googling the formula so I have tried here.

µTracer Question.jpg

[martin manning]

The definition is the same as for triodes. The uTracer will calculate it for pentodes, but you can ignore it. The reason is because pentode curves are nearly horizontal, and the number will vary wildly with even a small variation in Vg1. Ra is also given as an "approximate" value on pentode data sheets for the same reason, and I wouldn't pay much attention to that either.

[dorrisant]

Today I noticed something strange. The plots did not look right. After further inspection, I have nothing for my -15 and -40 volt supplies. Cannot calibrate at all. Doesn't matter if the computer is connected or not. No dice.

[martin manning]

After further inspection, I have nothing for my -15 and -40 volt supplies...

See here: https://ampgarage.com/forum/viewtopic.p ... 41#p447541 I suspect you have run into this issue. Pull transistor T2 and confirm it's shorted with a DMM. If so, replace it, and in any case add the two resistors shown to make its life easier. Plenty available: https://www.mouser.com/ProductDetail/ST ... tVBA%3D%3D

[dorrisant]

I replaced T2 and the 100Ω resistor under the board. All seems to be well now.

Another question: If using the uTmax GUI, is it a requirement to use the associated firmware? I only ask because I tried it out last night but it would hang up on the current calibration through the cal wizard. Other than that all seems to be fully functional.

Is there a procedure t0 upgrade the firmware through the uTracer or uTmax software? It seems that you can upgrade the firmware on a previous version of uTmax but not the latest.

[martin manning]

I replaced T2 and the 100Ω resistor under the board. All seems to be well now.

What about the 4k7 across the inductor? Both of those are soldered to pads on the underside of the board.

Another question: If using the uTmax GUI, is it a requirement to use the associated firmware? I only ask because I tried it out last night but it would hang up on the current calibration through the cal wizard. Other than that all seems to be fully functional.

Is there a procedure t0 upgrade the firmware through the uTracer or uTmax software? It seems that you can upgrade the firmware on a previous version of uTmax but not the latest.

I do not know much about the uTMax, but any firmware update is going to require reprograming the PIC, or replacing it with a pre-programed one.
uTMax was originally aimed at increasing voltage and current capability of the original uT3, which was 300V and 200mA. With the 3+'s 400V capability and high-current mod (set up for 600 mA), it's fine for me. I'm using Ihor's uTJS interface almost exclusively now because it's faster, and most importantly, it runs on iOS.