What is the collective noun of tube?

There isn't a widely accepted collective noun for "tube."

Here are some options depending on the context:

General:

* Bundle of tubes

* Set of tubes

* Collection of tubes

* Group of tubes

Specific:

* A rack of test tubes

* A row of vacuum tubes

* A bank of organ pipes (if referring to musical tubes)

Ultimately, the best collective noun will depend on what kind of tubes you are talking about and the context of your writing.