Switching tubes in a radio is a good simple test, but still requires some
basic organization. I remember using a radio to test a batch of 6CB6 tubes.
I tested about ten old unboxed tubes and found two of them were bad.
Unfortunately, I had grouped the tubes into different groups of similar
performance. A couple bad, a couple very hot, some middle of the road and
so on. When I got done, I had forgotten where the bad tubes were, so had to
start over again.

Before a friend died, he requested that I purchase his collection of 14,000
used tubes - which I did. Fortunately, my wife was away and I got them home
and stored before she got home. It was weeks before she figured out there
was something new in my collection.

But, having 15,000 tubes (I had 1,000) is something like a curse. The last
time I needed a particular tube, I could not find it and had to buy one.
Found it 2 months later.

73, Colin K7FM