Since I do not have a tube tester to test 24 and 27 tubes, if I can get a hum [or buzz] with signal injector from grid of tube to speaker, can I assume tube is good [woorking]?

Not necessarily. All it may mean is that the tube is not totally clapped out.

:Not necessarily. All it may mean is that the tube is not totally clapped out.
:
What u mean by"clapped out"????? shorted?????

Hi

Most old tubes will still operate. What you are doing is a reasonable test. Hum by touching grid #1 should be louder than touching plate pin. This gives an idea of gain.

Norm

::Not necessarily. All it may mean is that the tube is not totally clapped out.
::
:What u mean by"clapped out"????? shorted?????
:

:Hi
:
: Most old tubes will still operate. What you are doing is a reasonable test. Hum by touching grid #1 should be louder than touching plate pin. This gives an idea of gain.
:
:Norm
:
:::Not necessarily. All it may mean is that the tube is not totally clapped out.
:::
::What u mean by"clapped out"????? shorted?????
::
:It sure would be nice if some one on here tested tubes for people with no tube tester. You pay postage both ways, maybe small fee. I done this once with gentleman about 70 mile east of me, but don't think he still with us. Just saying !
:

At any given time, eBay has a decent selection of tube testers. Most testers made in the 50s were still capable of testing the big-pin tubes like the 24, 26, 27, 45, and so on.

"Clapped out" = worn out, low emission. Tubes will pass signal until their heaters burn out, but they usually cease to be functionally-useful long before that. All injecting a high-level signal into a tube grid and getting a plate response can tell you is that the tube is not totally inert. It implies no level of "goodness".