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* http://w140.com/ragsdale_661_1963.pdf
* http://w140.com/ragsdale_661_1963.pdf
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The Tektronix 661 is a [[sampling oscilloscope]] that was [[introduced in 1961]].   
The '''Tektronix 661''' is a [[sampling oscilloscope]] that was [[introduced in 1961]].   
It accepts two plug-ins: a sampling unit and a timing unit.   
It accepts two plug-ins, a sampling unit and a timing unit.   


Four sampling units were made:  
Four sampling units were made:  
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* [[5T3]]
* [[5T3]]


== Inter-module Signals ==
== Inter-module signals ==
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 Ω coaxial cables in the scope connect the sampling unit to the timing unit.   
One of these cables sends the "internal trigger signal" from the sampling unit to the timing unit.   
One of these cables sends the "internal trigger signal" from the sampling unit to the timing unit.   
The other cable sends the "start sample signal" from the timing unit to the sampling unit,  
The other cable sends the "start sample signal" from the timing unit to the sampling unit, telling it when to sample.   
telling it when to sample.  The connectors used for the inter-module
 
coaxial connections were made by Gremar.  The connector on the plug-in side  
The connectors used for the inter-module coaxial connections were made by Gremar.  The connector on the plug-in side  
is a Gremar 8212A. The connector on the scope side is a Gremar 8205A.
is a [[Gremar connector|Gremar 8212A]]. The connector on the scope side is a Gremar 8205A.
When operating one or both of the plug-ins outside of the 661, the sampling unit still
When operating one or both of the plug-ins outside of the 661, the sampling unit still
needs the sampling pulse from the timing unit.  The Gremar extension cable,  
needs the sampling pulse from the timing unit.  The Gremar extension cable, part number 012-070 (shown below) enables that.
part number 012-070 (shown below) enables that.


== Triggering Modes ==
== Triggering modes ==
A 661 can be triggered in at least four distinct modes:
A 661 can be triggered in at least four distinct modes:
* The 4S1 uses a trigger pickoff transformer to produce the internal trigger signal that can trigger the timing unit.  The 4S1 is the only 661 sampling unit that produces an internal trigger signal.
* The 4S1 uses a trigger pickoff transformer to produce the internal trigger signal that can trigger the timing unit.  The 4S1 is the only 661 sampling unit that produces an internal trigger signal.
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=== Power Supply ===
=== Power Supply ===
The power supply is typical of  
The power supply is typical of Tektronix scopes of early 1960s. An [[OG3]] tube is used as a voltage reference for the +300 V supply.
Tektronix scopes of early 1960s.
The other supply voltages use the +300 V supply as their reference.  The +19 V and -19 V supplies use BJT-based regulators.   
An [[OG3]] tube is used as a
The other regulators are tube-based.
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.


=== Indicator ===
=== Indicator ===
The indicator is a conventional X-Y indicator.   
The indicator is a conventional X-Y indicator.  The total CRT accelerating voltage is 3 kV and the vertical and horizontal amplifiers are  
The total CRT accelerating voltage is 3kV and  
relatively mild differential amplifiers made of [[6DJ8]] tubes and [[OC170]] germanium bipolar junction transistors.  
the vertical and horizontal amplifiers are  
The vertical and horizontal amplifiers have feedback loops around them that determine their gain.
relatively mild differential amplifiers made of [[6DJ8]] tubes
and [[OC170]] germanium bipolar junction transistors.  
The vertical and horizontal amplifiers have feedback loops around them  
that determine their gain.
The 661 uses a [[T5030]] CRT with P2 [[phosphor]].
The 661 uses a [[T5030]] CRT with P2 [[phosphor]].


=== Calibrator ===
=== Calibrator ===
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
tube.  It produces clippped sine waves at frequencies from 100kHz to 100MHz and
from 100 kHz to 100 MHz and amplitudes from 1 mV to 1 V. The output is 50 Ω [[GR-874 connector]].
amplitudes from 1mV to 1000mV. The output is 50 Ω [[GR-874 connector]].
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.   
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.   
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.   
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=== Delayed Pulse Generator ===
=== Delayed Pulse Generator ===
The delayed pulse generator is  
The delayed pulse generator is a [[tunnel diodes|tunnel diode]] circuit that produces a negative-going 250 mV pulse with a risetime of about 150 ps and a pulse width of about 400 ns.  The output is a 50 Ω [[GR-874 connector]].
a [[tunnel diodes|tunnel diode]] circuit  
When a timing unit (e.g., a 5T1) triggers, it sends a pulse through pin 10 of the J4 interconnect to the delayed pulse generator, which regenerates the pulse.
that produces a negative-going 250mV pulse  
There are three versions of the 661 delayed pulse generator (serial numbers 101 through 2829, 2830 through 3459, 3460 and up).
with a risetime of about 150 ps  
All three versions use a 50 mA, 6 pF germanium tunnel diode to generate the actual output pulse.
and a pulse width of about 400 ns.   
In early 661 production, a [[1N3130]] tunnel diode was used. Then it was replaced by a [[TD1081]].
The output is 50-ohm GR-874.
The circuit versions also differ in how they bias and trip the output tunnel diode.
When a timing unit (e.g., a 5T1) triggers,  
it sends a pulse through pin 10 of the J4 interconnect
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.
All three versions use a 50mA 6pF germanium tunnel diode  
to generate the actual output pulse.
In early 661 production, a [[1N3130]] tunnel diode was used.
Then it was replaced by a [[TD1081]].
The circuit versions also differ in how they
bias and trip the output tunnel diode.


Based on the available schematics,  
Based on the available schematics, the 661 appears to have been designed in 1961.   
the 661 appears to have been designed in 1961.   
:''During what years was it manufactured?''
During what years was it manufactured?
:''Why is it that the 661 has a dedicated high-speed coaxial interface between the sampling unit the timing unit while later 560-series sampling systems ([[3S2]], [[3T77A]], etc.) simply use the regular plug-in connector and mainframe wiring harness for routing trigger and timing signals between the two units?''
Why is it that the 661 has a dedicated  
high-speed coaxial interface between  
the sampling unit the timing unit while  
later 560-series sampling systems ([[3S2]], [[3T77A]], etc.)  
simply use the regular plug-in connector  
and mainframe wiring harness  
for routing trigger and timing signals between the two units?


Some 661s have a 41 pin Bendix connector on the rear panel, perhaps to allow the 661 to be interfaced to low speed data acquisition equipment or a computer.  This is essentially a pass-through from J2 & J3, the secondary multi-pin connectors on the vertical & horizontal plug-ins.  These connectors carry switch position information (number, magnitude & units) and clock & gate pulses. Not all plug-ins had this 2nd connector; the [[5T1A]] does, while the [[5T3]] does not.   
Some 661s have a 41 pin [[Bendix connector]] on the rear panel, perhaps to allow the 661 to be interfaced to low speed data acquisition equipment or a computer.  This is essentially a pass-through from J2 & J3, the secondary multi-pin connectors on the vertical & horizontal plug-ins.  These connectors carry switch position information (number, magnitude & units) and clock & gate pulses. Not all plug-ins had this 2nd connector; the [[5T1A]] does, while the [[5T3]] does not.   


The 661 has a 137°F [[thermal cutoff]].   
The 661 has a 137°F [[thermal cutoff]].  In practice, it doesn't run hot.
In practice, it doesn't run hot.


The Tektronix 012-064 is a plug-in extension cable for the 661.
The Tektronix [[012-064]] is a plug-in extension cable for the 661.


==Specifications==
{{MissingSpecs}}


==Links==
==Links==


* [http://readingjimwilliams.blogspot.com/2013/06/scope-sunday-45.html Reading Jim Williams: Scope Sunday #45]
* [http://readingjimwilliams.blogspot.com/2013/06/scope-sunday-45.html Reading Jim Williams: Scope Sunday #45]
* A 661 can be seen in the [https://www.youtube.com/watch?v=I9m2w4DgeVk Tektronix film on Transmission Lines].


==Pictures==
==Pictures==


<gallery>
<gallery>
File:661_top_int.jpg|top internal view
661_top_int.jpg | top internal view
File:661_front.jpg|front view
661_front.jpg | front view
File:661_trace.jpg|trace with 10 samples/cm and 2x horizontal expansion
661_trace.jpg | trace with 10 samples/cm and 2× horizontal expansion
File:661_left_int.jpg|left internal view
661_left_int.jpg | lleft internal view
File:661_rt_int.jpg|right internal view
661_rt_int.jpg | right internal view
File:Tek_661_rear.jpg|rear view (fan removed)
Tek_661_rear.jpg | rear view (fan removed)
File:Tek_661_solder.jpg|close-up of solder & inspection markings
Tek_661_solder.jpg | close-up of solder & inspection markings
File:4s1_top.jpg|top view of 4S1
4s1_top.jpg|top view of 4S1
File:4s1_timing_pulse_connection.jpg|Coaxial interconnect from timing plug-in goes through the mainframe, into the 4S1, and ends here, at the sampler.
4s1_timing_pulse_connection.jpg | Coaxial interconnect from timing plug-in goes through the mainframe, into the 4S1, and ends here, at the sampler.
File:4s1_sampling_bridge.jpg|This is the sampler.  The GaAs sampling diodes are arranged in a diamond shape and are directly connected to the socket from the delay line.
4s1_sampling_bridge.jpg | This is the sampler.  The GaAs sampling diodes are arranged in a diamond shape and are directly connected to the socket from the delay line.
File:4s1_delay_connection.jpg|The delay line is a coil of coax going from the trigger pickoff to the sampler.
4s1_delay_connection.jpg | The delay line is a coil of coax going from the trigger pickoff to the sampler.
File:661_timing_interconnect.jpg|The 661 mainframe has two pieces of 50-ohm coax that connect the sampling unit bay to the timing unit bay.  The plug-ins engage with these interconnects when inserted.
661_timing_interconnect.jpg | The 661 mainframe has two pieces of 50 Ω coax that connect the sampling unit bay to the timing unit bay.  The plug-ins engage with these interconnects when inserted.
File:4s2_4.jpg|4S2 top view
4s2_4.jpg | 4S2 top view
File:4s2_3.jpg|4S2 front view
4s2_3.jpg | 4S2 front view
File:Tek 661 extension.JPG|012-064 plug-in extension cable for 661
Tek 661 extension.JPG | [[012-064]] plug-in extension cable for 661
File:Tek_gremar_extension_012-070.jpg|012-070 Gremar Extension Cable
Tek_gremar_extension_012-070.jpg | [[012-070]] Gremar Extension Cable
File:Tek 661 d992 mod.png|Mod described in June 1963 Service Scope regarding the delayed pulse generator
Tek 661 d992 mod.png | Mod described in June 1963 Service Scope regarding the delayed pulse generator
</gallery>
</gallery>


[[Category:Sampling scopes]]
[[Category:Sampling scopes]]
[[Category:661 series scopes]]
[[Category:661 series scopes]]
[[Category:Specifications needed]]
Retrieved from "https://w140.com/tekwiki/wiki/Special:MobileDiff/23806"

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