John Kobbe recently jotted down his recollections of Tek's development of the 500 Series oscilloscopes. Starting with the 310/315 he charts the evolution of many developments, including Howard Vollum's desire to incorporate plug-in vertical amplifiers, and build our own CRT's and stop using our competitors' tubes. Internally we long suspected Dumont and RCA were shipping us their culls, saving their best CRT's for themselves.
This is an interesting read, even inserting the development of the 570 tube curve tracer, and the 575 transistor curve tracer that enabled engineering to characterize tubes and transistors to further the performance of their designs. John describes 1n 1957 when HP introduced a scope with a 100x sweep magnifier. HP, they theorized, must have thought they had us because our post accelerator CRT design limited us to 5x magnification. Beyond that, the beam hits the deflection plates, and secondary electrons are accelerated forward to the display area, creating blobs of light on the screen, worsening at higher magnifications. Solution, paint the CRT plates with the carbon material used for making the spiral resistor. It made the problem look better, and allowed us to produce a 533/543 with a 100 times magnifier.