uTracer (Micro Curve Tracer)

[martin manning]

Muahahahaha!

The parts kit was a bit under $300, and the enclosure and other hardware was maybe another $150. I also bought a DC bench supply for power rather than run it with a laptop PC brick. The DC supply is a much better way to go with its digital display to monitor operation, cleaner power, current limiting, and of course it will be useful for other things. All together something approaching $600, I guess? Still a bargain for what it can do, and it's not just an experimenter's toy.

[martin manning]

More uTracer madness...

A few days ago I tested an old TV horizontal sweep tube with a plate cap. This is basically a 6L6 that has been modified for high voltage use. At first I got the crumpled curves shown in the top plot, and not knowing quite what to make of that I asked.

This is likely the result of oscillation, I was told, and that adding a grid stopper might cure it. I thought I'd try a ferrite on the plate lead (Radio Shack, 2 for $3), since bringing the plate connection out of the box bypasses all of those little ferrites on the socket wiring. This cured the problem nicely, as shown in the lower plot.

The second attachment is a screen shot (from the uTracer web pages) of the recently added Quick Test forms which control a test around a single-point, like a traditional tube tester. Plate current, Ra, Gm, and mu are measured and reported, with dual triodes tested simultaneously (the screen supply is used as the plate supply for the second section). Most data sheets have specs at 250V (plate and screen), so the uTracer can get there with 50V to spare, and the complete set-up for this test (and full curve tracing) can be stored and recalled later. I'm asking for some additional inputs to include the nominal values of Ra, Gm, and mu.

I'm seeing quite a bit of variation in both new production and NOS tubes using the Quick Test feature, which we all knew was there, I guess. Now I'm even less likely to buy NOS tubes without some guarantee of their condition. I do see a correlation between a darkened getter flash and poor performance, so beware of that.

[ToneMerc]

Martin this is very cool, like a poor man's MaxiMatcher. thanks for sharing.

TM

[martin manning]

Thanks! The Maxi-Matcher is not a curve tracer, so the uTracer is more like a poor man's Amplitrex (which sells for $2675!). The uTracer's voltage limits are lower than either of those, but its current capability is the highest of the three since a pulsed measurement technique is used. There is more flexibility here too, since any tube type and any bias point (within limits) can be tested.

[Reeltarded]

You look like you are having fun. I have a vacation idea for you...

[ToneMerc]

Thanks! It's more like a poor man's Amplitrex (which sells for $2675!), since the Maxi-Matcher is not a curve tracer. The uTracer's voltage limits are lower than either of those two, but its current capability is the highest since a pulsed measurement technique is used. There is more flexibility here too, since any tube type and any bias point (within limits) can be tested.

I've drooled over the Amplitrex many a time. Hmmmm, maybe you should make TAG special run of these.

TM

[martin manning]

For anyone interested, there is now a user manual for the uTracer posted on Ronald Dekker's web site (see under "The User Manual" in the left column): http://dos4ever.com/uTracer3/uTracer3.html
I served as editor, and in a flurry of effort on both our parts this got done over the weekend. I have no financial interest in this project, just plenty of intellectual interest.

[cbass]

So everyone send their tubes to Martin to test he said he would even replace the ones that tested bad with good ones for free.

Seriously that is badass you are a genius

[VacuumVoodoo]

Massive body of work, impressive.

[martin manning]

So everyone send their tubes to Martin to test he said he would even replace the ones that tested bad with good ones for free.

Seriously that is badass you are a genius

Not me- think about this: R Dekker designed the thing from the ground up and wrote the 14,000-word manual in another language!

[Jack Hester]

Martin -

I'm very impressed with your invested time, on this instrument. I recently purchased one, to build over the Winter. I am just now discovering this thread, and have it bookmarked. I will try to post pictures of my contruction, but thinking it will be drawn out for a while. Thanks for sharing this information. I'll need it.

Jack

[martin manning]

That's great, Jack! I'll be happy to help where I can, and probably be posting updates here as I get more experience. Get a good soldering rig if you don't have one already- there are some fine-pitch pads on the board.

[Jack Hester]

That's great, Jack! I'll be happy to help where I can, and probably be posting updates here as I get more experience. Get a good soldering rig if you don't have one already- there are some fine-pitch pads on the board.

I do need to use something different, for this build, as my typical soldering setup is more geared towards tag boards and p2p builds. Nothing very precise.

I'll try not to be a worry, but will post any issues (hopefully not many) along with all the positive that I'm sure will result.

Jack

[martin manning]

More uTracer. This is a test of a 6L6GC, an RCA black-plate, no less. The Quick Test result, which probably has the widest appeal, is shown below. At 81% of the spec current ("emission") for the chosen bias point, this tube is usable, but a bit tired. Also shown are gm and ra, at 5.23 mA/V and 38.22 kohm. The specs are 6.0 and 22.5, so 87% and 170% respectively. Notice I had to increase the set-point voltages a bit to nail the spec anode and screen voltages in the actual test. That is not a calibration issue, it's just the way the thing works.

Traditional tube testers set some (usually unknown) operating point to measure emission (reported on percent scale), and then put a small AC signal on the grid to measure gm. The uTracer can be set to test at the data sheet spec point, and reports ra, mu, and screen current in addition to plate current.

The second plot shows the anode curves for 250V screen voltage, the same as in the Quick Test. I ran the full trace and then ran the Quick Test, and chose "keep plot," so the data for the Quick Test has been added to the anode curves (it's the hen-scratch at the lower right). Quick Test runs six points around the spec center condition, ~10% above and below the Va, Vs, and Vg, from which gm, ra, and mu are calculated. The anode voltage for the first screen voltage perturbation seems a bit off... Not sure why that is, but it shouldn't affect gm here, only the screen voltage derivative. Edit: This may be a bug. Investigation is ongoing.

The photo shows the test set-up including the small B&K power supply delivering 20V at 440 mA. The uTracer draws 200 mA at idle, but the heater is switched on here. You can see part of a cat in that picture too :^)

[martin manning]

The issue with the odd looking voltages for the Quick Test points is apparently due to the hardware needing a bit more time to stabilize when anode or screen voltage is going in the downward direction. All voltages are supposed to be at the center point or +/- 10%, but Va wasn't getting back to the set point after going high, and Vs wasn't getting down to -10%. Vg was hitting +/- 10% with no problem, and this doesn't happen without a tube connected. Fortunately there is a user input to add some delay to allow for stabilization of the tube being tested. I tried some of that (2s) and it cures the problem. A small tweak to the software to add some delay in the Quick Test will probably put this to bed, but it would be nice to fully understand what is going on.