I thought about pincushion but have never heard of anyone have that problem on this old of set. Would you degauss from the front or the back side, or no matter?

I'm not going to get within 5" of this CRT so doing anything inside the cabinet while it's on is something I can't risk...not with my unsteadiness (from medication). If I am going to do any demagnetizing, my only options are outside while it's on or inside when it's off.

Degaussing coils are still relatively available due to the prevalence of old arcade units with standard CRTs.

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.

Monochrome tube does not have a shadow mask. In this case you want to run the degaussing coil all around the bell.

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.

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

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.

If that’s the case, maybe I should get the cheap wand style on eBay. I’d have to find a way to get 220V to it.

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.

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.

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

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.

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.

https://live.staticflickr.com/65535/...a4159cce_z.jpg

https://live.staticflickr.com/65535/...a835166e_z.jpg

https://live.staticflickr.com/65535/...84803dbb_z.jpg

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