500-series plug-in connector

500-series scopes (53x, 54x, and 55x) and 127, 132, 133 have bays that take letter-series and 1-series plug-ins which typically control the vertical axis of the display. Two exceptions are the 555 and the 536. The 555 takes four plug-ins: Two letter-series and 1-series plug-ins control vertical deflection of the two beams. Two 555-specific timing/sweep plug-ins (21, 22, 21A, 22A) control the horizontal deflection of the two beams. The 536 takes two letter-series or 1-series plug-ins; the left one controls vertical deflection and the right one controls horizontal deflection. 580-series scopes use their own plug-ins.