291
The Tektronix 291 Diode Switching Time Tester Power Supply was introduced in 1963. The 291 uses the TF-1 test fixture.
TF-1 fixtures have been known to have issues with bad connections with the diode. In at least one case, a TF-1 has been made to work reliably by replacing the weak AlNiCo magnet that holds the axial leaded (magnetic) diode in place, by replacing it with a much stronger FeNdB magnet the same size (easily available on Ebay). The TF-1 was later superseded by an adapter 017-0075-00 to be used with the diode test jig 013-0075-00.