[R-390] Best R 390A Tube Tester

[Doug Millar]

The best R 390A tube tester is a set of substitution tubes. Most tube 
testers only measure tube performance at low frequencies and may not give a 
good picture of what the tube is like. I am trying to find an article 
written in the '50s that described the workings of most tube testers and 
their limitations. The final suggestion was to use substitution.
	Doug K6JEY