The Tektronix Type G is a plug-in differential amplifier for 500-series scopes.
Unlike the Type D, the Type G is optimized for RF, achieving only a 100 to 1 common-mode rejection ratio but operating all the way to 20 MHz. Unlike "comparator" plug-ins such as the Type W and Type Z, the Type G does not contain an internal precision variable voltage source. It is for measuring the difference between two externally applied input signals. Its maximum sensitivity is 50 mV/div. It has seven tubes. (The early, slower 53G has five tubes.)
Its name changed twice. Type 53G was introduced in March 1955 along with the 541/545, but it was only specified to 10 MHz in a 535, and its performance in a fast mainframe was not documented. When the mainframe cabinet styles were revamped in August 1956, the Types 53A, 53B, 53C and 53G were all upgraded (sped up) and renamed; Type 53G became Type 53/54G. It was the only early plug-in that did not go through the awkward "53x/54x" phase. In 1959 it became Type G with no further change in design. It was dropped after 1970.
Types G and K are the only letter-series plugins where the Gain vernier is not concentric with the step attenuator.