211

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Tektronix 211
500 kHz miniature analog scope
Tektronix 211

Produced from 1971 to (?)

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The Tektronix 211 is a 500 kHz single-channel miniaturized analog battery-powered oscilloscope.

Specifications

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Internals

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 an amplifier IC, U25, part number 155-0057-00.

Triggering is done using a 155-0048-01.

The 211 uses a 155-0047-00 for X and Y amplification until the final stages, which use NPN transistors to drive the CRT deflection plates.

The CRT is a 154-0642-00 (<B080000) or 154-0699-00.

Background

Regarding his experience as a Tektronix manufacturing engineer for the CRTs for the Miniscope series (211, 212, 213, and 214), Dale Dorando recalls:

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 CRT's 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 4 operators. The yield and volume for the Miniscope CRT became much higher than the conventional CRT's.

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 CRT's, 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.

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