[Amps] Question: looking for a design for a simple test fixture for4-125A

[k7fm]

"I just would love to find out if these tubes will work and pull current and 
handle some voltage."

In the 1930's, hams did not have tube testers - so they tested each tube 
manually by setting applying some voltages, measuring current, then 
calculating gain of the tube.  You can actually some testing with a filament 
transformer, a couple of analog or digital volt and current meters and a pot 
(or vaiable voltage source.

Not long ago, I wanted to know if a big old 211 was any good.  I set up a 
filament transformer, used a 9 volt battery for the plate supply, a 
microammeter for a plate current meter, another voltmeter for the grid. 
Then, I varied the grid voltage and logged the plate current change with a 
change in grid voltage.  Surprisingly, the gain was calculated in the ball 
park.

No, this will not test the tube under actual operating conditions - but at 
least you will be able to compare one tube with another and see if you have 
any real duds.  No, it is not like testing the tube on 6 meters.  But, you 
have a crude tube tester with not much expenditure in time and no money. 
Test the tube as a triode, strapping the screen to the plate.

The good news is that you do not have to worry about getting shocked.

73,  Colin  K7FM