565

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Tektronix RM 565
10 MHz dual-beam scope
Tektronix RM 565

Produced from 1962 to (?)

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The Tektronix Type 565 is a dual-beam scope that takes two 560-series vertical plug-ins. It was introduced in 1963.

A rackmount version, the RM565, was also produced. Aside from being dual-beam, the 565 is unusual among the other 560-series scopes in the fact that it (the mainframe) has built-in trigger, sweep, and horizontal amplifier circuits.

Specifications

The vertical characteristics are mostly determined by the vertical plug-ins.

The fastest sweep is 1 μs/div (100 ns/div with 10x horizontal magnification enabled). The sweep delay can be adjusted over a range from 10 μs to 50 seconds.

Power consumption, including plug-ins, is about 600 watts, maximum.

The internal calibrator produces a 1 kHz square wave with amplitude selectable in decade steps from 1 mV to 100 V.

Circuits

The 565 uses the T5650 CRT.

Vertical Signal Path

As is usual for 560-series scopes, the vertical deflection plates of the CRT are driven directly, differentially, by pins 17 and 21 of the vertical plug-in. The left plug-in bay is for the lower beam and the right plug-in bay is for the upper beam.

A 0.7—3 pF trimmer capacitor is connected immediately behind each of the plug-in connectors, and allows for the mainframe to be calibrated so that plug-ins can be interchanged without requiring the high-frequency compensation of the system to be readjusted. The capacitance seen by the plug-in driving the scope should be 14.3 pF for either beam.

There is no trigger pickoff in the vertical signal path of the 565. That function is performed by the plug-ins.

Trigger and Sweep

The triggering signal comes from pin 11 on the plug-ins, is amplified by a 12AT7-based cathode follower, and sent to "TRIGGER" switches. From there, the trigger signal is sent through a 6DJ8-based differential amplifier and then is discriminated by a 6DJ8-based Schmitt trigger.

The 565 is also unusual in that it employs a tunnel diode (D845, a TD4, which is equivalent to the 1N3718) in the trace intensification circuit. The tunnel diode forms a bistable multivibrator: kick it one way and it turns on and stays on, kick it the other way and it turns off and stays off. The tunnel diode is DC-coupled to the base-emitter junction of Q843, which is a 2N404 germanium PNP transistor. Because the tunnel diode and transistor are DC-coupled, the transistor needs to be germanium. This is one of the rare cases when a failed germanium transistor cannot be replaced with a silicon part. Contrast this with the timebase A trigger of the 585A, which uses a tunnel diode AC-coupled to a transistor, which makes the forward voltage of the transistor's base-emitter junction irrelevant.

Calibrator

The calibrator is an astable multivibrator formed by one half of a 12AT7 and a 6AU6. The other half of the 12AT7 serves as the output cathode follower for the calibrator.

Comparison with the 556

The 565 appears similar to the 556, but is different in many ways. The 556 uses tunnel diodes for triggering, while the 565 uses tubes. The 556 uses letter-series and 1-series plug-ins while the 565 uses 560-series plug-ins. Moreover, the bandwidth of the 556 is specified as 50 MHz, while the bandwidth of the 565 is specified as 10 MHz. Subjectively, the trace of the 565 is very sharp, sharper than the trace of the 556.

Mechanical

Benchtop (565) and rackmount versions (RM565) were made. The benchtop version has the following dimensions:

  • Width: 17 inches
  • Height: 13.5 inches
  • Depth: 23.375 inches
  • Weight: 62 pounds

Pictures

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