No affiliation - but I think what this is, is an adapter to allow additional TV chassis' types to be connected to your 8JP4, 8YP4 and 8XP4 test picture tubes. I think.

http://www.ebay.com/itm/Anchor-Chek-Tube-Convertor-TC-438-CRT-Tester-Box-Instructions-NOS-/261016388670?pt=BI_Cellular_Optical_Television_Tes t_Equipment&hash=item3cc5ca043e

Cool. It even covers the Predicta CRT filament voltages.