Hickok CA-4 Adapter Sale is for one of the two CA-4 adapters in the pictures.
According to the brochure the CA-4 adapter can be used with other tube testers other than Hickok and is a "Universal Adapter". The CA-4 adapter preceded the CA-5 adapter.
Tube data for the CA-4 data can be found at Bama and it has all the data for about any Hickok tube tester, but if you need me to send it to you it will be sent as a PDF file via email. Read the brochure in the pictures for more information. The brochure is not included.
 
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