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The Tektronix Type 531 is a 10 MHz oscilloscope that accepts letter-series and 1-series plug-ins. It is exactly like Type 535 except it does not have the Delayed Sweep (dual timebase) feature.

The 531 and 535 were the first Tektronix scopes to accept plug-ins. It was introduced in March 1954 simultaneously with the Type 535, and superseded in 1959 by the Type 531A, which has more convenient controls and a slightly faster (15 MHz) vertical amplifier.

In serial numbers 101 to 7600, the 531's L-C delay line is before the vertical amplifier. In serial numbers 7601 and up, the 531's delay line is between the vertical amplifier and the CRT. This change was the result of John Kobbe's insight that if the far end of the delay line was an open circuit (which the CRT approximates), the reflected wave could be absorbed at the source end. This "single termination" approach made it possible to do away with the output chassis. All Tek scopes using a lumped-constant delay line went to this topology.

There is also a rack-mount version, Types RM31 and RM31A. They have a sliding chassis so that the scope can be serviced without removing it from a rack.

The 532 is similar to the 531, but designed to be more reliable at the expense of slower risetime. The 541 is mostly the same as the 531, but has a distributed vertical amplifier for 30 MHz bandwidth, and a different CRT.


     — 531 SN 101-7600
Bandwidth DC to 10 MHz (≤ 3 dB) with Type A plug-in
Rise time 0.035 μs
     — 531 SN 7601 up & 531A
Bandwidth DC to 15 MHz (≤ 3 dB) with Type K plug-in
Rise time 0.024 μs
     — all
Line Voltage 108/115/122/216/244 VAC ±10%,selected via primary voltage selector and voltage range selector switches, 50 Hz to 60 Hz.
Thermal Protection Automatic resetting thermal cutout, in case internal temperature exceeds safe operating level
Power Consumption 475W with plug-in
Cooling AC Fan
Trigger Modes AC/DC/AC LF Reject, and HF Sync
Anode Potential 10 kV (relative to cathode)
Screen Area 6 cm × 10 cm
Construction Aluminum alloy chassis. Anodized front panel
Weight 61,5 lbs / 27,8 kg

Pictures of 531

Pictures of 531A

Pictures of RM31A