While there were many leads available for Hickok testers and many card options for the Card-O-Matics to fill out their sets, there were three main options that were necessary over the years to backdate or update the testers.
The first is the CA-4 option. This consisted of a set of later sockets mounted in an adapter to allow testing of late tubes such as compactrons and minature tubes for testers such as the 546 which lacked that capability. The knobs made certain that the correct signals whent to the right pins.
The CA-5 adapter on the other hand was used to allow later testers lacking early sockets to test tubes such as the four pin 83 regulator tube used in every Hickok tester prior to the 580.
Next is the RSP-4 module which could replace the standard socket set in a 6000 (lacking 4 pin and other sockets) and allow testing of the early tubes. Later buyers were given the option of either module on purchase.
A final adapter is the CA-99 which was used as an add-in to the model 799 "Mustang" tester to extend its capabilities.