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Revision as of 20:03, 28 April 2010

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calibration signal generator and a high-speed pulse generator, but
calibration signal generator and a high-speed pulse generator, but
otherwise it is just a low-speed X-Y indicator.  The total CRT accelerating voltage is 3kV and the vertical and horizontal amplifiers are relatively mild differential amplifiers made of 6DJ8 tubes.  The sophistication of the 661 is all in the plug-ins.  The signal from the calibration generator is available on the front panel and is also sent to the timing generator through the multi-pin plug-in connector.  This allows the timing plug-ins to select "CAL" as a trigger source.  In this mode, the calibration generator can be used as the stimulus for the device under test.  In many situations, this eliminates the need for external triggering.  When the timing unit triggers, a pulse is sent to the high-speed delayed pulse generator in the 661, which triggers and outputs a positive 250mV pulse about 400 nanoseconds long.  The rising edge of this pulse is very fast.
otherwise it is just a low-speed X-Y indicator.  The total CRT accelerating voltage is 3kV and the vertical and horizontal amplifiers are relatively mild differential amplifiers made of 6DJ8 tubes.  The sophistication of the 661 is all in the plug-ins.  The signal from the calibration generator is available on the front panel and is also sent to the timing generator through the multi-pin plug-in connector.  This allows the timing plug-ins to select "CAL" as a trigger source.  In this mode, the calibration generator can be used as the stimulus for the device under test.  In many situations, this eliminates the need for external triggering.  When the timing unit triggers, a pulse is sent to the high-speed delayed pulse generator in the 661, which triggers and outputs a positive 250mV pulse about 400 nanoseconds long.  The rising edge of this pulse is very fast.
The 4S1 is a dual-trace sampling unit for the 661.  Each channel has a trigger pickoff, a delay line, and a sampler.  The sampling pulses for each channel are generated by a step recovery diode are are fed to a sampling bridge made with of GaAs diodes.  These diodes are fragile and exact replacements are hard to find.  People have improvised replacements using modern integrated Schottky diodes such as those in HP/Agilent's HSMS-28x series.
The 4S1 has a dual-trace mode, where the A waveform and the B waveform are both displayed in the time domain at the same time with a single trigger source and a single equivalent-time sweep rate.  Another mode of is called "A vert/B horiz".  This mode is used in conjunction with an X-Y mode switch on the panel of the 661 to allow arbitrary external control of the sampling point instead of a linear or random equivalent-time sweep.


The 4S2 is very similar to the 4S1, but has faster rise time.  This
The 4S2 is very similar to the 4S1, but has faster rise time.  This
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