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The Tektronix 211 is a 500kHz single-channel miniaturized analog battery-powered oscilloscope.
{{Oscilloscope Sidebar
|manufacturer=Tektronix
|series=200-series scopes
|model= 211
|summary=500 kHz miniature analog scope
|image=Tek 211 front.JPG
|caption=Tektronix 211
|introduced=1971
|discontinued=1976
|designers=Dave Allen
|manuals=
* [[Media:070-1163-00.pdf|Tektronix 211 Operator]] (OCR)
* [[Media:070-1160-00.pdf|Tektronix 211 Maintenance]] (OCR)
}}
The '''Tektronix 211''' is a 500 kHz single-channel miniaturized analog battery-powered oscilloscope.
The 1 MΩ input probe is directly wired to the instrument. External trigger and horizontal inputs are provided via banana jack.
The 211 "Miniscope" was developed by a group led by [[Dave Allen]].


The probe input first goes through compensated attenuators and then into one gate of Q18, a dual JFET.
{{BeginSpecs}}
The drains of the dual JFET drive the inputs of an amplifier IC, U25, part number [[155-0057-00]].
{{Spec | Bandwidth | DC to 500 kHz (100 kHz at 1 mV/div) }}
{{Spec | Input Impedance | 1 MΩ // 130 pF }}
{{Spec | Input Voltage | max. 600 V DC + peak AC, or 600 V<sub>p-p</sub> AC  }}
{{Spec | Sweep Range | 200 ms to 5 μs  per division }}
{{Spec | CRT | [[154-0642-00]] (<B080000) or [[154-0699-00]], 6(V) × 10(H) }}
{{Spec | Battery Runtime | 3-5 Hours with maximum intensity  }}
{{Spec | Battery | 10 rechargeable NiCd cells }}
{{Spec | Line Voltage | 110-126V <sub>AC</sub> ±10%, 58−62 Hz }}
{{Spec | Power Consumption | < 2 W @ 126 V<sub>AC</sub>, 60 Hz}}
{{Spec | Dimensions  | (H/W/D) 3" × 5.2" × 8.9" (7.6 cm x 13.2 cm x 22.6 cm)  }}
{{Spec | Weight | 3 lbs/1.38 kg }}
{{EndSpecs}}


Triggering is done using a [[155-0048-01]].
==Internals==
===Vertical===
The probe input first goes through compensated attenuators and then into one gate of Q18,
a dual JFET. The drains of the dual JFET drive the inputs of dual output amplifier IC  U25,
part number [[155-0057-00]]. U25 drives one section of dual output amplifier U105 [[155-0047-00]]  which drives CRT V-plates via  output transistors Q110/Q107.


The 211 uses a [[155-0047-00]] for X and Y amplification until the final stages,
===Horizontal===
which use NPN transistors to drive the CRT deflection plates.
Triggering is done using  U65 [[155-0048-01]], which contains a horizontal amplifier (for external), trigger, and sweep generator.
The output of U65 drives the second section of dual output amplifier IC  U25 [[155-0057-00]] whose output is fed to the H-plates via output transistors  Q119/Q122.
U65 is mounted on the input board. The unblanking signal from U65 is driven to CRT via Q134.


* [http://w140.com/Tek211_OpSVC.pdf Tektronix 211 Manual (PDF)]
===Power Supply===
Tek 211 can be operated from line power or the internal Ni-Cd battery. Line power is also used for charging the batteries. Internally the unit uses a DC-DC converter to generate the required voltages from the battery or line, using Q242, Q249, and T250. DC-DC converter generates
the +5.6 V, -5.6 V, and +65 V used in the unit. -1 kV for CRT is generated using a voltage multiplier.
 
Instead of the transformer, a capacitive divider is used to step-down down the line voltage. C210 is the capacitor for providing charging voltage and C212 gets parallel to C210 for line operation. The value of these capacitors needs to be adjusted based on operating line frequency and voltage. Manual suggests recommended values of these capacitors for common line frequency and voltages. Input AC must be sinusoidal to offer the correct reactance to step-down the line voltage.
 
Like other instruments of the era, there are no filter capacitors in the power supply, rather the battery is used as the filter capacitor. Hence disconnecting the battery can affect the unit's operation.
 
==Background==
 
Regarding his experience as a Tektronix manufacturing engineer for the CRTs for the Miniscope
series (211, [[212]], [[213]], and [[214]]), [[Dale Dorando]] recalls:
<blockquote>
I worked under [[Bill Johnson]], one of the manufacturing managers, especially the
flood guns used in the storage CRT's.
I was the weld lab manager too.  We designed, tested, selected electrodes, and weld
settings for the elements inside the CRT.
 
The CRT division had a great concept where the new engineers work at each station
for a week or two learning all the processes and actually making parts.  The side
advantage is you meet the production people and when you need something you know who
to ask.
 
The CRTs for the 211, 212, 213, and the storage version, 214, were manufactured
using a pilot program where the same assembler worked on all phases of the tube.
The other CRT's were being built by a person that only did one portion of the
assembly. As an example, the deflection plates were assembled and carefully aligned,
the next operator may not realize that and if accidentally bent, tried to bend them
back. Naturally they wouldn't be properly aligned. By having the same people
perform every process, they could see what was important and what could be improved.
The primary goal was to find ways to improve the processes.  By performing all
the steps it was easier to find these improvements. The result was that with just
these four operators, the yield and volume for the Miniscope CRT became much higher
than the conventional CRTs.
 
The cathode for the Miniscope CRT was a critical part of the design.  It took
several tries to get that right.  It was being done in conjunction with our partner,
Sony.  Sony was to use the same 1/4 watt cathode in the Trinitron TV.
The cathode was a direct heated type - the filament and cathode were on the same
flat wire.  This reduced the power necessary to heat the cathode to the required
temperature.  This was important for a battery operated device.  The spacing
between the cathode and the grid with extremely important for the intensity and spot
size. If the filament deformed while being heated, the cathode could move.  The
filament had springs that kept it taught across a ceramic ring inside the grid cup.
The cathode was a small disk with the triple carbonate coating blown on to the
surface at a precise thickness.
 
As with most of the Tektronix CRTs, it used deflection blanking where the beam is
aimed off the screen during the horizontal retrace.  This was faster and easier to
control with the associated electronics than changing the negative high voltage with
respect to the grid.
 
Glass rods hold the elements in place inside the CRT.  Having so many elements
embedded in such a small glass rod made them fragile.  The rodding process was
carefully controlled for temperature and time.
 
The bulb of the CRT was ceramic with an internal gold plating as the anode.  The
bulb was frit-bonded at high temperatures to the glass neck.  The faceplate was also
frit-bonded to the ceramic bulb.  The faceplate was first silkscreened with the
graticule.  After the faceplate was bonded to the bulb, the phosphor was allowed to
settle in a liquid onto the faceplate.  The liquid was poured out and then aluminum
pellets were evaporated on to the phosphor in a mild vacuum.  The aluminum helped
resist burning the phosphor and reflected the light from the back to the front for a
brighter sweep.
 
The electron gun was welded to the stem with the pins.  That was inserted into the
neck, that was previously bonded to the ceramic bulb, and using a lathe with a
torch, melted the stem to the neck.  The CRT was evacuated and the metals
inductively heated to remove the gasses in the metal, then sealed.  The getter was
inductively flashed to a size dictated by a template for that CRT.  The larger the
flash, the better is absorbed the impurities, but too much flashing could short out
metal parts.
 
A coil was wound around the CRT to allow for a trace rotation adjustment in the
oscilloscope.  This would correct for any small gun rotational alignment.
</blockquote>
 
==See Also==
* [https://www.youtube.com/watch?v=BJTZIawR1Iw LazyElectrons Video: Tektronix 211 - Internals, battery replacement]
 
==Prices==
 
{| class="wikitable"
|-
! Year
! 1973
|-
! Catalog Price
| $545
|-
! In 2023 Dollars
| $3,800
|}
 
==Pictures==
 
<gallery>
Tek 211 front.jpg
Tek 211 front.JPG  | 211 Front view
Tek 211 right2.JPG | 211 RHS
Tek_211-wHood.jpeg | 211 with Viewing Hood Part [[016-0199-00]]
200 series compared.jpg | Tek [[214]] (top), [[213]] (center) and [[211]] (bottom) stacked
Tek_211_Vs_555.jpeg | Size comparison, 211 vs. [[555]]
Tek_211-BatLevel.jpeg | 211 Battery charge meter
Tek_211-Internal-Top.jpeg | 211 Internal top
Tek_211-Top-WoAmp.jpeg | 211 Top w/o amplifier board
Tek_211-Internal-Bottom.jpeg | 211 Internal bottom
211 int 01.jpg | 211 Internal bottom w/o PS board
Tek_211-Int-Side.jpeg | 211 Internal LHS
211 int 05.jpg | Input Board (rear)
Tek_211-Inputboard.jpeg | Tek 211 Input board (rear)
211 int 08.jpg | Input board front (w/o front panel)
211 int 02.jpg | Amplifier board
211 int 03.jpg | Amplifier board
211 int 06.jpg | Amplifier board (trace side)
211 int 04.jpg | Power supply board
Tek_211-PSBoardwBat.jpeg | Power supply board and battery
211 int 07.jpg | Power supply board (trace side)
Tek_211-OPTransistors.jpeg | Output transistors
Tek_211-PS-Capacitor.jpeg | Dropping caps in power supply
Tek 211 battery pack.jpg|Tek 211 internal battery pack
</gallery>
 
==Components==
{{Parts|211}}
 
[[Category:200 series scopes]]
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