Vacuum tube/thermionic valve measurement tool project

[Greg Robinson]

Hi everyone,
I'm new to the forum, and new to digital electronics. I work with analog circuits, primarily vacuum tubes.

First, some background on my project:
I'm hoping to design a specialist tool for measuring the operating parameters of vacuum tubes in new and existing designs.
It would be for observing power pentodes and beam tetrodes in power amplifiers, and I would like to measure a number of parameters:
 a: cathode voltage relative to ground
 b: cathode current (low side)
 c: control grid voltage relative to cathode
 d: control grid current
 e: screen grid voltage relative to cathode
 f: screen grid current (high side)
 g: anode voltage relative to cathode
 h: anode current (high side)

Obviously the high voltages involved in tube circuits will present some challenges (I would like to be able to measure circuits under operating conditions, such as transformer coupled push-pull power amplifiers, where peak voltages could reach up to 1.5kV), and relative voltage measurements and high side current measurements will need to be opto-coupled and will require isolated power rails.

I'm intending to develop this using the Arduino platform, and have recently acquired a Mega2560 board to familiarize myself with the environment.


So, my question is this:
I would like to use A/D converters with higher bit depth than the Arduino 10bit analog channels, preferably I would like to use 14 bit or higher for at least some of my inputs so as to retain high resolution over a wide input range and without resorting to any range switching, however, I am unsure how to accomplish this due to my unfamiliarity with digital circuits. I was hoping someone could advise me if this is possible, and how to approach it, or direct me to a source where I could learn more.

Thank you in advance for any assistance anyone can provide, and hope that you find my project interesting!

[commongrounder]

Hello Greg, and welcome to the forum!

A couple of questions for you:

Is this project intended to be a tester/analyzer that has in-line plug/sockets to allow parameter testing of tubes in a real world environment?  What is the ultimate purpose of the data gathered, and in what form will it be, i.e. raw for computer analysis or for numerical readouts?

I am interested in your project as I do much service work on tube audio electronics.  It is always a challenge to accurately assess how a tube is functioning in a working circuit.  This would be an interesting blend of venerable old and fresh new technology!

[EV]

Maybe you have seen this:

http://www.dos4ever.com/uTracer3/uTracer3.html

[Greg Robinson]

Hi commongrounder,
Yes, that is exactly my intention. An inline socket as found on many "bias-meter" type contraptions, but with much greater scope. The aim being to gather as much data as possible on tubes under operating conditions.
I intend to equip the tool with a display device (most likely TFT) that can display voltage, current, dissipation, as well as min/max/average.
With the quality of current production tubes being variable and questionable, it's often difficult to determine the actual cause of failures - I would be able to use such a tool to test tubes to destruction and observe what the fault was. I would also be able to use it to test new (or existing) designs to ensure that they do not cause the tube to exceed maximum ratings.
Hopefully this project will result in something that will be useful to others as well.

Thanks EV, that looks interesting, it's not something I have seen before. Not quite what I have in mind, but may help provide some inspiration.

[Excavatoree]

Maybe you have seen this:

http://www.dos4ever.com/uTracer3/uTracer3.html

Holycrap!  I'm glad I didn't bust out 1500 dollars (US) or more, I can't remember, for the computerized Hickok cardmatic tube tester.

Sounds like a great project.  Ever priced a Tek 570?