The Tektronix 7403N is a 65 MHz oscilloscope mainframe that takes two 7000-series vertical plug-ins and one 7000-series horizontal plug-in. It has a large CRT (8 × 10 divisions @ 1.22 cm each, 154-0640-xx or 154-0672-xx tubes). There is no readout system.
There are two versions, the benchtop 7403N with the CRT above the plug-ins, and a rackmount version, the R7403N, with the CRT to the left of the plug-ins.
The 7403 was designed from the ground up. Phil Crosby led the design. The design team decided to use a discrete transistor vertical output amplifier rather than a hybrid on beryllium oxide. The output stage approximated a 3 pole MFED response with an additional real pole closer to the origin. Since the DC requirement was 3 screen diameters, the gain at the -3db point could be substantially less, meaning that the load resistor (and output stage dissipation) could be reduced, allowing the design to meet scan bandwidth and corner shift criteria with substantially reduced power dissipation.
The 7403N was discontinued around 1975, having been superseded largely by the popular 7603 introduced in 1973. In 1974, the 7403N had a list price (without plug-ins) of $950. In the same year, the 7603 was $1600.
The 7403N consumes a maximum of 130 watts and uses convection cooling, no fan. It weighs 30 pounds.
The power supply is a linear design, similar to that of the 7313. The vertical and horizontal amplifiers are made of discrete bipolar transistors. The only integrated circuit in the vertical signal path is U214, the vertical channel switch, a 155-0022-00.
The 7403N uses a CRT anode voltage of 12 kV, produced by a solid state voltage multiplier.