A 350 MHz spectrum analyzer plug-in for use in the 18x-series oscilloscope displays. The 18xT-series displays are preferred because they include rear-panel connectors for an X-Y plotter.

The 8557A (and certain other models) use a construction technique in the rotary switches that becomes a problem with age. The switches are made with a plastic drum with spring-finger wipers that are attached with only a tiny nib of plastic that is melted in a hole (like a tiny plastic rivet). With age, the plastic has weakened, and the wipers break off. The wiper pieces are often lost. Re-attaching an original or fabricated replacement wiper is challenging. An alternative repair strategy is to replace the entire switch with an external switch cabled outside of the chassis. This is feasible because (typically) the switches are switching low-speed logic circuits, NOT high-speed analog signals. Consult the schematic to see if it may work in a particular case.

Below is an 8557A installed in a 182T display, showing the spectrum of the FM broadcast band.