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661 (view source)

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The timing units use [[tunnel diodes|tunnel diode]] triggering.   
The timing units use [[tunnel diodes|tunnel diode]] triggering.   
Two 50-ohm coaxial cables in the scope connect the sampling unit to the timing unit.   
Two 50-ohm coaxial cables in the scope connect the sampling unit to the timing unit.   
One cable sends the trigger pickoff signal (if available) from the sampling unit to the timing unit.   
One of these cables sends the trigger pickoff signal (if available)  
The other cable sends the timing signal from the timing unit to the sampling unit, telling it when to sample.
from the sampling unit to the timing unit.   
The other cable sends the timing signal  
from the timing unit to the sampling unit,  
telling it when to sample.
 
The 661 mainframe essentially consists of four subsystems:
* power supply
* indicator
* amplitude/time calibration signal generator
* delayed pulse generator
 
The power supply is typical of
Tektronix scopes of early 1960s.
An [[OG3]] tube is used as a
voltage reference for the +300V supply.
The other supply voltages use the +300V
supply as their reference.  The +19V and -19V supplies
use BJT-based regulators.  The other regulators are tube-based.
 
The indicator is a conventional 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 vertical amplifier has a feedback loop around it
that determines the gain.


The mainframe of the 661 is quite simple. 
A significant fraction of the sophistication of the 661 is in the plug-ins.
It contains a 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 vertical amplifier
has a feedback loop around it that determines the gain.
The amplitude/time calibrator is a Colpitts oscillator that uses a [[7119]]
The amplitude/time calibrator is a Colpitts oscillator that uses a [[7119]]
tube.  It produces clippped sine waves at frequencies from 100kHz to 100MHz and
tube.  It produces clippped sine waves at frequencies from 100kHz to 100MHz and
amplitudes from 1mV to 1000mV.  The output is 50-ohm [[Connectors#GR-874|GR-874]].
amplitudes from 1mV to 1000mV.  The output is 50-ohm [[Connectors#GR-874|GR-874]].
The delayed pulse generator is a [[tunnel diodes|tunnel diode]] circuit
that produces a negative-going pulse with a risetime of about 150ps. 
The output is 50-ohm GR-874.
The signal from the calibration generator is available on the front panel and  
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.   
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.   
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 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. 
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 4S2 is very similar to the 4S1, but has faster rise time.  This
The delayed pulse generator is a [[tunnel diodes|tunnel diode]] circuit
is partly due to the elimination of the trigger pickoff and [[delay line]]
that produces a negative-going 250mV pulse with a risetime of about 150 ps
on each channel.  Since the 4S2 does not provide a pickoff signal to the
and a pulse width of about 400 ns.   
timing plug-in, when using a 4S2 only one of the coaxial
The output is 50-ohm GR-874. 
interconnect cables in the 661 carries a signal.  The timing unit
When the timing unit triggers (e.g., a 5T1),
gets the trigger signal either from external input or from the internal
it sends a pulse through pin 10 of the J4 interconnect
pulse source in the 661.   
to the delayed pulse generator, which regenerates the pulse.
There are three versions of the 661 delayed pulse generator.
The first is in serial numbers 101 through 2829.   
The second version is in serial numbers 2830 through 3459.
The third version is in serial numbers 3460 and up.


Based on the available schematics, the 661 appears to have been designed in 1961.   
Based on the available schematics, the 661 appears to have been designed in 1961.   
Retrieved from "https://w140.com/tekwiki/wiki/Special:MobileDiff/6305"

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