Tube Matching Strategies

[Martin Manning]

For those who are using uTracer to match power tubes, what is your preference? 

- A "perfect" tube specimen would match the spec Ia and Gm at the spec Va, Vg2, and Vg1.

- Consider the use case to be a push-pull amplifier, where Vg1 is adjustable, but all tubes will operate at the same DC Vg1 (at zero signal).

- The goal of "Matched" tubes is generally understood to be that they will exhibit the same Ia and Gm at some Va and Vg2 (often nearly equal to Va), and some Vg1 which is chosen to meet a target anode dissipation at zero signal.

- Typical practice would be to test a batch of tubes, sort them by the measured parameters, and then choose pairs showing similar results.

- uTJS has two options for QuickTest: 

Specified Va, Vg2, and Vg1, measure Ia, Ig2, and Gm

Specified Va, Vg2, and Ia, measure Vg1, Ia, Ig2, and Gm

Assuming a single point test is used to select matched pairs:

Which of the above test types do you prefer and why?

What measured parameters do you sort by and in what order?

How are the matched pairs chosen and by what criteria?

Thanks,

MPM

[Big Josh]

Also need to consider the percentage that is considered matched. Some people say within 5%, some say within 20%. 

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[Martin Manning]

That's where I was going with the third question: How are the matched pairs chosen and by what criteria?