This is a Hickok 752A that I restored electronically and calibrated. This is a very nice tester and is very clean. The 752A has the ability to test a multi section pre-amp tube without having to re-do the settings for the second section. You just make the settings according to the tube chart, test the first section, then select the second section and make the tests in the second section.
The tester came to me with a blown Bias fuse so tubes could not be tested. The Bias fuse is used to protect the Bias potentiometer if incorrect settings are made for the tube being tested. When it is blown, the Bias voltage is not applied to the tube.
The 752A has the ability to test the older and newer tubes, including compactrons.