Two Way Hourglass Bends on My KCS47

[Chris K]

I guess I could put the chassis and yoke back in the unit with the weak CRT and see if it produces a proper image. That would all but confirm Penthode's suspicions of a magnetized CRT bell.

[old_tv_nut]

A thought: is it possible this set is intended to have some anti-pincushion magnets or pole pieces that are missing?

[Chris K]

Originally Posted by old_tv_nut

A thought: is it possible this set is intended to have some anti-pincushion magnets or pole pieces that are missing?

I don’t see any on either set. It does have permanent magnets in the focus ring but they are a ways away from the tube.

[Penthode]

Originally Posted by old_tv_nut

A thought: is it possible this set is intended to have some anti-pincushion magnets or pole pieces that are missing?

The fixed anti pincushion magnets only appeared with the later wide deflection angle CRTs in the 1960s. I recall seeing them on later sets.

The 70 degree tubes like the 16GP4 generally did not suffer from pincushioning or raster distion unless there was a strong external magnetic field nearby.

My guess it is a magnetized cone are the corner distortions as the beam reaches a sweep extremity.

[Penthode]

I would think the best thing to do is to remove the tube from the set and go over the tube with a color TV degaussing coil.

[Kevin Kuehn]

Originally Posted by old_tv_nut

A thought: is it possible this set is intended to have some anti-pincushion magnets or pole pieces that are missing?

I haven't noticed any on the 2 or 3 sets I've had here with 16GP4's. If that was a thing wouldn't it be listed on the 16GP4 data? I have seen magnets on newer rectangular tube yoke assemblies.

[Penthode]

Originally Posted by Kevin Kuehn

I haven't noticed any on the 2 or 3 sets I've had here with 16GP4's. If that was a thing wouldn't it be listed on the 16GP4 data? I have seen magnets on newer rectangular tube yoke assemblies.

It wouldn't normally be a problem with a 16GP4. Unless in the past the tube was subjected to a strong magnetic field.

[Kevin Kuehn]

One thing that bothers me about this set Chris is working on is that the raster apparently won't fill the mask. I would definitely be verifying the power supply voltages.

[Kevin Kuehn]

For some perspective here's my Sentinel with a 19AP4 crt. You can definitely see some outward bowing, which seems quite normal for one of these big flat face tubes. Some of it is distortion from the face curvature. Never mind the guy peeking out from inside the TV.

[Chris K]

Originally Posted by Kevin Kuehn

One thing that bothers me about this set Chris is working on is that the raster apparently won't fill the mask. I would definitely be verifying the power supply voltages.

Definitely going to do that Kevin. Like I said before I never checked it because the rectifier is new.

[Chris K]

And there’s no mention of anything like that in the Rider’s service info which has an extensive setup section

[Chris K]

Wow!

[Penthode]

The slight bend is normal. It is due to the geometry of the CRT. The greater the deflection angle, the greater the bend.

The 15GP22 color CRT has a flat panel screen mounted internally within the tube. Because of this, the pincushion is very noticeable.

Wider deflection angle tube used pincushion correction. For monochrome sets, permanent magnets were used. For color, the introduction of the 25" rectangular CRT in 1965 required dynamic pincushion correction circuitry because permanent magnets would affect color purity.

I still contend the bell of the replacement 16GP4 has become slightly magnetized and removing the tube and carefully going over it with a degaussing coil will alleviate the problem.

[bandersen]

Perhaps it was intentional to counteract the outward curve of the CRT face in metal cone CRTs?

[Chris K]

Originally Posted by bandersen

Perhaps it was intentional to counteract the outward curve of the CRT face in metal cone CRTs?

Problem for me is it can be seen when the image has straight lines in it. As you get towards the center it’s not noticeable but it is the last 2” or so of the vertical and horizontal limits of the tube