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The Tektronix 321 is a very compact single-trace,  
{{Oscilloscope Sidebar
single-timebase portable oscilloscope  
|manufacturer=Tektronix
that is almost completely solid state.   
|series=300-series scopes
It was [[introduced in 1960|introduced on April 8th, 1960]].
|model=321
The 321 includes several germanium bipolar transistors,
|summary=Portable single channel scope
which are a known reliability problem. 
|image=Tek 321 trace.jpg|321 front view
The 321A was [[introduced in 1964]].
|caption=Tek 321 front
The 321 and 321A have slightly different circuits. 
|introduced=1960
Early instances of the 321 (sn pre-720) use a
|discontinued=1972
[[5718]] peanut tube as the front-end cathode follower. 
|designers=Oz Svehaug;Oliver Dalton;Hiro Moriyasu
Later 321 and 321A use a [[7586]] nuvistor for that role. 
|manuals=
In several circuits, the 321 uses [[OC170]] transistors
* [[Media:070-196.pdf|Tektronix 321 Manual 070-196]]
where the 321A uses [[2N2207]] transistors.
* [[Media:070-0425-01.pdf|Tektronix 321A Manual 070-0425-01]] S/N 100-5999 (OCR)
* [[Media:Tek 321 irb.pdf|Tektronix 321 Instrument Reference Book]] (OCR)
* [[Media:Tek 321a mod 128A.pdf|Tektronix 321A Mod 128A]]
* [[Media:070-0891-00.pdf|Tektronix 321A SN 6000 up]] (OCR)
* [[Media:321 announce.pdf|Tektronix 321 Announcement]]
* [[Media:070-425.pdf|Tektronix 321A Manual]] (OCR)
* [[Media:tek_321_fcp.pdf|Tektronix 321 factory calibration procedure]] (bad-OCR)
* [[Media:Tek 321a fcp june 1968.pdf]]
* [[Media:Tek 321 mod 797A.pdf]]
* [[Media:Tek 321 mod 799F.pdf]]
* [[Media:Tek 321 single sweep lockout early schematics.pdf]]
* [[Media:Early tek 321 schematics.pdf]]
}}
The '''Tektronix 321''' is a very compact single-trace, single-timebase portable oscilloscope that is almost completely solid state.   
Design work took place in 1959 and it was [[introduced in 1960|introduced on April 8th, 1960]].
It was designed by [[Oz Svehaug]], [[Oliver Dalton]], and [[Hiro Moriyasu]].


[http://bama.edebris.com/manuals/tek/321a/ Tektronix 321A manual]
The 321 includes several germanium bipolar transistors, which are a known reliability problem.


[http://w140.com/tek_fcp/tek_type_321_factory_cal_proc.pdf Tektronix 321 factory calibration procedure]
The '''321A''' was [[introduced in 1964]].  The 321 and 321A have slightly different circuits. 
Early instances of the 321 (sn pre-720) use a [[5718]] peanut tube as the front-end cathode follower. 
 
Later 321 and 321A use a [[7586]] Nuvistor for that role. Latest 321A (SN6000 up) use a FET [[151-1011-01]].
In several circuits, the 321 uses [[OC170]] transistors where the 321A uses [[2N2207]] transistors.
 
==Power Supply==
The 321 uses a DC-DC converter to generate the DC voltages needed for the scope.
Prior to serial number 720, 321s used the [[120-153]] transformer along with a separate high voltage power supply with its own transformer
the +3350 V CRT anode voltage.
Starting at serial number 720, all DC voltages (including the CRT anode voltage, via a voltage multiplier) are generated by a single power supply
based on the [[120-210]] transformer.
 
{{BeginSpecs}}
{{Spec | Bandwidth      | 5 MHz (321) / 6 MHz (321A)  }}
{{Spec | Rise time      | 70 ns (321) / 64 ns (321A)  }}
{{Spec | Sweep          | 0.5 μs/Div to 0.5 s/Div, 1–2–5, ×5 magnifier (i.e. to 50 ns/Div) }}
{{Spec | Deflection      | 10 mV/Div to 20 V/Div }}
{{Spec | Input impedance | 1 MΩ // 35 pF }}
{{Spec | Calibrator      | 0.5 V<sub>p-p</sub>, about 2 kHz  }}
{{Spec | CRT            | [[T3210]] or [[154-433|T3211-31]] or [[154-433]], P31 phosphor, 10 × 6 Div. @ 6.25 mm (0.25"), 4 kV acceleration }}
{{Spec | AC Power        | 90–136 V or 180–272 V, 20 W }}
{{Spec | DC Power        | 11.5–35 V, 8.5 W min., 24.5 W max., 700 mA current typ. }}
{{Spec | Battery        | Ten size "D" NiCd cells, runtime 5 h (4 Ah cells), 3 h (2.5 Ah cells), charge time 16 h }}
{{Spec | Dimensions      | 21.67 cm × 14.6 cm × 40 cm (8.5" × 5.75" × 16") }}
{{Spec | Weight          | unknown, about 5 kg }}
{{Spec | Features |
* Ext Trig / X input (supports X-Y displays)
* External blanking input (Z modulation)
* Built-in battery
}}
{{EndSpecs}}
==External Power Connector==
Douglas W Jones wrote:
<blockquote>
I've got a Tektronix 321 scope (serial number 001917) that I need to run from an external
DC supply.  The problem is, I have only the line cord, and not the
DC cord.  The power input plugs on the scope are obviously
custom, long predating the standard IEC plug everyone uses today.
 
So I improvised.  The pin spacing for the 3-pin DC input plug is
very close to the spacing of Molex 6, 9 and 12-pin plugs, and the
pin diameter is not too much larger than Molex uses.  So, I
picked up a 6-pin Molex housing and 3 female molex pins, and
then cut the housing down to 4 pins (using my pocket knife).
 
I used an old IEC cord for the DC input wires, with the plugs cut
off both ends.  I attached the wires on one end to the molex pins
and pushed them into the housing, then jammed to housing down
onto the Tektronix connector (this flared the female Molex pins
to fit the Tektronix pins.  The other end of the DC power cord got
banana plugs to fit the output posts of my DC power supply.
 
The net result works fine, plugs and unplugs nicely, and unlike
other power supply solutions I've seen, involves no changes to
the scope.
</blockquote>
<div style="padding-left: 3em;"><gallery>
Dwj tek 321 ps connector.jpg|321 External Power Connector
Dwj tek 321 ps cable.jpg|Douglas W Jones' 321 External Power Cable
</gallery></div>
<blockquote>
Added note:  My bench supply has an analog Ammeter on it.
The starting surge of the 321 is about 1.5 amps, perhaps 2,
tapering down to 0.7 amps in under a second.  It seems to draw
a steady 0.7A regardless of what you're doing with it.  The
current drain doesn't change when you vary the supply from 12 to
18V — this is because the 321 uses a linear regulator.
</blockquote>
==Links==
* [https://sites.google.com/site/johnengsdeadtechrescue/photos/john-s-ideas-to-restore-dead-technology/repair-challenge-tektronix-321-oscilloscope--the-first-transistor-oscilloscope Repair Challenge Tektronix 321 Oscilloscope]
==Pictures==


<gallery>
<gallery>
Image:321_front.jpg|front view
tek-321-front.jpg | 321 rectangular front
Image:321_right_case.jpg|right case
tek-321-round-front.jpg | 321 round front
Image:321_left_internal.jpg|left internal
tek-321-round-vs-rect.jpg | 321 round vs. rectangular models
Image:321_right_internal.jpg|right internal
321_pair.JPG | 321 and 321A
Image:321_rear.jpg|rear view
321_front.jpg|321 front view
321_right_case.jpg|321 right case
321_left_internal.jpg|321 left internal
321_right_internal.jpg|321 right internal
321_rear.jpg|321 rear view
Tek 321 round.jpg|321 with round bezel
321A_FET.JPG|Latest 321A's frontend
Tek 321a trace.jpg|321A trace
Tek 321a trace2.jpg|321A trace
321SN1557.jpg|321 with no model number on panel
Tek 321a bottom.jpg|321A bottom view
</gallery>
</gallery>
{{Parts|321}}
{{Parts|321A}}
[[Category:Portable scopes]]
[[Category:300 series scopes]]
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