The Tek 575 Transistor Curve Tester can be used to measure tubes like the twin triode 12AX7 (which has a 12V heater requirement) and the 6DJ8 (which uses 6V at the heater). The 575 can sweep collector (plate) voltage between 0 and 200 Volts, which is a useful range for these tubes. All the 575 is missing is a heater supply, and a suitable tube socket.
I constructed a tube adapter that can plug in to the banana plug sockets on my 575’s DUT panel, using a panel from a parts 575 I acquired years ago (to replace the bad CRT tube in my original 575). The angled faces on the panels combine to result in a horizontal surface, which I used to mount the tube socket (B9A), a pair of terminals for an external heater supply (I used a 6VDC wall wart adapter rated at 300mA), and a single pole double throw (SPDT) switch to select between 12V and 6V tube types.
Here is the completed adapter, measuring the transfer curves for a 12AU7A dual triode.
One convenient aspect of the wiring in the adapter is that the tube’s two triodes can be compared easily by flicking the 575’s transistor A/B select switch. This allows an instant comparison of the transfer curves, and shows how well (or badly) they match.