The Tektronix Type 541 is a 30 MHz* oscilloscope that accepts letter-series and 1-series plug-ins. It has a distributed amplifier and is exactly like the Type 545 except it does not have the Delayed Sweep (dual timebase) feature.
It was introduced in 1955 simultaneously with the 545, and was superseded in 1959 by the 541A, which has more convenient controls. For example, the 541 required the operator to set two rotary switches to get the desired sweep time/div . The 541A replaced the two-switch design with a many-position rotary switch. This was also the case with setting the calibrator amplitude, which involved two switches on the 541 and one switch on the 541A.
There is also a 541-S7 version, which has single-sweep mode.
* 33 MHz with a 50 MHz plug-in such as the Type 1A1.