These are some early bulletins and publications from Tektronix
Phase Angle Measurements
This Electronics December 1954 ad features the Type 531 and 535 oscilloscopes which were the first to feature plug-ins. The Type 53 plug-in featured dual trace.
Note the ad for a free booklet on how to do phase angle measurements.
Here is the Phase Angle booklet. Click on the image to view the PDF.
These 1955 bulletins compare new products features and announce phase out of older products. We especially like the obsolescence notice for the 512 with tnew orders will be built on a "when-we-get-to-it" basis, whatever that means. Click on the image to view the PDF.
This March 27, 1956 bulletin appears to be a summarization of an Electronics February 1944 article on on using load lines to set triode bias. We cannot find the original Electronics magazine. Click on the image to view the PDF.
Fundamental Electronic Concepts For Oscilloscope Use & Maintenance 1956
This 1956 document describes a number of electronic concepts as visualized on an oscilloscope. Click on the image to view the PDF.
Using The Oscilloscope As An Instrument Maintenance Aid 1958
This paper was presented at the 1958 Instrument Automation Conference. It covers basic oscilloscope operation. Click on the image to view the PDF.
Factors Affecting Scope Value 1961
This document is an excerpt from the 1961 catalog on the value of Tektronix products. Click on the image to view the PDF.