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The Tektronix S-4 is a sampling head for 7000- and 3S-series samplers. It was designed by George Frye and introduced in 1968. It is the fastest of the S-series plug-in samplers.

During the development of the S-4, the velocity gate theory was tested using a length of transmission line between diodes. This led to a aperture time that depended upon twice the propagation delay of the length of transmission line.

Key Specifications

Rise time 25 ps (observed with S-50 or S-52, 35 ps)
Bandwidth 14.5 GHz
Input impedance 50 Ω (terminated SMA connector)
Input range 1 Vp-p (operating)
Maximum input ±5 V max. non-destructive
Noise < 5 mV
  • trigger signal pick-off for internal triggering


The S-4 sampling gate is based upon a traveling wave trapped-charge transmission line in which the sampling window is set by the propagation time of a pulse edge through a thick-film transmission line. This technique requires only a sharp pulse edge rather than a precise pulse width, which is harder to generate. The sampling diodes are housed in a special coaxial connector that provides a high bandwidth signal path.

To disassemble the sampler hybrid, first remove it from the sampler board as per the manual. Remove the input connector using a 7/32" wrench and remove the 20 dB attenuator with small pliers. The ceramic board is held to the housing using roll pins that can be pressed out with a 0.030" pin punch. The hybrid has six diodes, each about 0.75mm square. The cathodes are glued to the gold substrate with conductive epoxy and the anodes are wire-bonded (twice) over a gap to the next step in the strobe line. It appears that a standard beam-lead diode may fit across the gap but cleanly removing a failed diode without damaging the substrate would be quite difficult.


1979: $1,435 (~$5,600 in 2022 Dollars)

According to an internal memo, in 1979 annual sales were estimated at 150 units.




Some Parts Used in the S-4

Part Part Number(s) Class Description Used in
152-0335-00 Discrete component step recovery diode S-4 S-6
152-0335-01 152-0335-01 Discrete component 150 ps step recovery diode 1502 S-2 S-4 S-6
155-0001-00 155-0001-00 Hybrid integrated circuit gate assembly S-4