Yokes, what's the difference?

[Don Lindsly]

Your thinking makes sense. Consider these factors as well. Maximum energy is at the center of the yoke. It is wound so as to deflect the beam with no neck shadows. Sharper deflection angles require flaring out the front to move the energy as close to the CRT bell as possible.

The yoke does look more like as inductor. The inductive energy stored during the trace scan is released on retrace. That energy is rectified by the damper and added to B+ to develop the higher boost voltage. The diode action also dampens the retrace ringing as well. To a point, higher inductance is beneficial. You will notice when you disconnect the yoke, the boost voltage decreases.

Cosign wound is intended to compensate for the varying distance from the electron gun to the screen, depending on beam position. With this compensation, linearity would be more difficult to achieve.

Don

[jeyurkon]

Thanks Don, that helps.

My question was mostly out of curiosity. In the 1957 Merit catalog they state that "there are six different types of deflections yokes, without regard to the deflection angle." It wasn't clear to me what they meant by the last part of the statement. They go on to say that several different manufacturers will use yokes with the same horizontal and vertical inductance's, but that the damping networks may be different. Merit tried to choose their networks to work with most sets.

Your comment about the bell shadowing is interesting. I'm having that problem with trying to use a 12LP4 in the Sylvania 1-108 chassis. I have to very carefully adjust the positions to avoid that. The yoke was designed to be used with a 10MP4 or 12VP4, but Sylvania also used the same part number yoke with a 16LP4 so I assumed it would work with the 12LP4. Of course I'm still operating it at a lower HV than is optimal for the 12LP4.

I tried various 12LP4s and I was surprised at the differences in the bell shapes. I thought they'd all be the same. On one the transition between the neck and the bell looks just like it does on a metal CRT.

John