Questions about Tube Testers
We use this circuit since 25 years, and it never went wrong.
This is an approach below any professional level. It's called trial and error. It's only done when you know nothing else to do.
Here is an example. I tried to convince my young daughter when crossing the street, to look AND to the left, AND to the right, AND then to the left again, AND not run, but walk. Reason being when she walks, a car driver can better see what she is doing.
She says too many AND. This is to difficult, and not needed. You can hear a car, and if needed, you just run away quickly. All her friends do that, and it never went wrong.
We very often see the same approach with tube rectifier circuits, and companies, calling themselves experts. They just try something, violating the data sheet, and when tubes survives, they say that's because they are 25 years experienced experts. This is not a joke! You don't need to search very long for that. If you see for instance an amplifier with a 5U4G rectifier with 100uF first capacitor on it, or 274B rectifier with 20uF, you just found a product made by a fake expert.