Dale Dieterle
Forum Participant

I bought a Stark 9-66A back in the late 1960’s,or 1970’s. I bought a universal add-on adapter, that came with installation instructions from Stark. This adapter screwed into the top compartment of the tester.The 9-66 models are based on the Hickok 533 circuits.There is four models,
the 9-66, 9-66U, 9-66A, 9-66AU. The only difference is the tube sockets that were added. The 9-66 has nine sockets, 9-66A has twelve sockets. The
9-66U has sixteen sockets including the adapter, that was factory installed. The 9-66AU has nineteen sockets installed at the factory. The 9-66 uses a 18 point filament switch,and the 9-66A, and 9-66AU use a 20 point switch,it has a off setting as well as a .63 volt setting. The 9-66’s use a signal voltage of 5 vac., same as the Hickok 533.
Hickok built tube testers for other company’s such as the Philco’s 9100
tube tester witch is identical to the 533A circuits.

Have a nice day,
Dale Dieterle