647

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The Tektronix 647 is a 50 MHz oscilloscope with plug-ins for both vertical and horizontal deflection. It was introduced in late 1963, along with a minimal set of plug-ins, and replaced by the higher bandwidth 647A in 1967. Except for the CRT and the rectifiers in the HV power supply, the 647 is all solid state.

The intent was to offer a higher performance scope in a small form factor, roughly the size and weight of the 560 series. Additionally, the 647 was promoted as “ruggedized” with an extended operating temperature range, and higher shock and vibration ratings than previous lab grade instruments.

The 647 uses 10 series vertical and 11 series time base plug-ins. At introduction, the 10A2 a dual channel 50 MHz vertical, 11B1 single time base, and 11B2 dual time base were offered. These plug-ins are unique to the 647 and 647A.

Specifications

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Internals

Unlike the threaded knob used for retaining the 530/540 series plug-ins, the 647 uses a lever actuated cam mechanism. The single lever both engages and disengages the plug-in with a quick, smooth motion. Many users considered it to be the best plug-in retaining system Tek had ever offered.

Unlike the 560 series where the plug-ins directly drive the CRT deflection plates, the 647 has amplifiers for both the vertical and horizontal signals in the mainframe. In addition to supporting the higher bandwidth, the amplifiers provide a normalized gain at the plug-in interface, eliminating the need to adjust the gain or sweep cal every time a plug-in was swapped.

The 647 has a 140 ns delay line between the vertical plug-in connector and the input of the vertical amplifier. The interface between the vertical plug-in and the mainframe is a 93 Ω controlled-impedance connection. This is in contrast to the 500-series scopes, which appear to the plug-in as a high impedance.

The horizontal and vertical plug-ins are not electrically interchangeable. Only a 10 series plug-in will work in the vertical compartment, and only a 11 series time base will work in the horizontal compartment. X-Y mode requires the use of the external horizontal input in an 11 series time base.

The 647 uses the T6470 CRT with electromagnetic trace rotation and 14 kV total accelerating voltage. The HV power supply contains five 5642 rectifier tubes: three for the +11.2 kV CRT anode supply, one for the -2.2 kV CRT cathode, and one for the -2.2 kV CRT grid/blanking.

The calibrator in the 647 is based on a 4 kHz crystal, which is divided down to 1 kHz. Its specified tolerance is +/- 1Hz.

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