The Tektronix 133 is an external enclosure and power supply for a letter-series or 1-series plug-in. It was introduced in 1961. The enclosure supplies power to the plug-in and the outputs from the plug-in are available. The bandwidth of the 133's outputs is 100 kHz, which is much slower than the 16 MHz bandwidth of the 132. However, the 133 has a 2 Ω output impedance compared to 5 kΩ for the 132, and the 133 can drive 1.5 amperes at its output, versus a maximum of 10 mA for the 132.