The Type 513 oscilloscope was introduced in 1950 and was in production 5 years. A 513D model which included a single-ended 40 L-C stage delay line was also available. The 513 utilized a distributed amplifier to achieve a flat bandwidth from DC to 20 MHz.
This advanced information for the 513 appeared in the March 1950 Northwest Electronics World magazine (really a 12 page flyer).
These two photos are from a Tektronix Photo Album, date unknown.
We have a Type 513D oscilloscope on display at the museum.