Tube Curve Tracer design

[bepone]

in practical use, measurements on PL95 small output pentode:

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some screens (screens and messages are rolling during measurements):

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overcurrent protection included and when happen PIC is switching off main contactor which is in incoming DC line , adding alarm message on the display.
this is tube tester and idea of curve tracer was always triggering me..so few years later i start to build also this...

[TUBEDUDE]

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[TUBEDUDE]

Miscellaneous thoughts;

Although an Arduino could do the job well enough, a $17 Raspberry Pi Zero W would be a good choice, hosting all of the UI natively (in Python...) and communicating through WiFi with a PC by VNC. Or, if you want to make a standalone machine instead of co-opting a used and possibly free laptop or older desktop machine, you can hook a display, keyboard, and mouse directly to the Pi.

Having looked at the situation a bit, I think that instead of using Hall effect current monitors, I'd use small shunt resistors floating in series with the plate, screen, and grid, and isolating differential amplifiers to get the currents out to A-D converters.

There are convenient 4 channel, 16 bit A-D converter modules available for $2.00 each on ebay, which offer two differential channels of A-D (and four single ended channels) that would be about ideal for converting the differential output of an isolating diffamp. They're only good up to 860 samples per second, so the speed of the measured signal would need to be limited to less than 400Hz. That may be OK for a tube characterizer, and is cheap for proof of concept. A second module gives you four single ended 16 bit channels, and could be used for measuring Vgrid, Vscreen, and Vplate, as well as a Voutput if you used appropriate resistor-capacitor scaling on the voltages.

So the front end measurement system looks like

Iplate: Sense resistor => Si8190 isolating diffamp => 2x channels of A-D#1 => host via i2C
Iscreen: Sense resistor => Si8190 isolating diffamp => 2x channels of A-D#1 => host via i2C
Vgrid: Resistor network divider => inverting opamp => 1x channel of A-D#2
Vplate: Resistor network divider => inverting opamp => 1x channel of A-D#2
Vscreen: Resistor network divider => inverting opamp => 1x channel of A-D#2
Voutput: Resistor network divider => inverting opamp => 1x channel of A-D#2

Reading all the outputs amounts to reading the channels via i2C on the two A-D's.

After that, it's ASMOP (A Simple Matter Of Programming).

Hmmmm... I don't know why this didn't strike me before - you could build a sampling probe head into an octal-socket standoff so you could do the actual sampling for a tube inside a functioning amp. The grid supply would be carried along on the measurement system, so you could insert the sampling head. Hmmm... no, wait - you build two sampling heads, so you can use it in a push pull amplifier and actually test the output stage separately from the rest of the amp. That saves you from having to build the power supply, OT and other appurtenances needed that are not the measurement system. Of course, it still works with a test bed separate from an amp, too.

Dang. More design to do.

That seems the way to go. Adds troubleshooting functionality for the amp power stage also.

[pompeiisneaks]

I don't know if R.G. had the time to pull together osme kind of schematic for this, I still have that board you sent me, and I have the pi and several arduino's. I'd be happy to build something. I've also gotten practice with SMD soldering and have an smd heat station and a microscope for tiny soldering. I'd be game to give this a go again, if you've got a more concrete design in mind?

~Phil

[cys]

^Another tracer option.

[Jim Hagerman]

I designed and built a curve tracer once. Not sure it will help anyone, but here is some design info...

http://www.hagtech.com/pdf/vacutrace.pdf