My Kriesler 79-2 is fitted with a 21DJP4 replacement CRT (21” 90 degree).

Pete, your Philips has the same CRT. It was a very popular replacement tube in the 60's and early 70's.

I have found it impossible to centre the raster using the centering magnets on the yoke without defocussing, loss of brightness and shading. Overall, when correctly focussed, the raster is about 10% down and to the left. The chassis can overscan the tube sufficiently to hide this but I find it annoying to lose so much of the picture.

Researching this, I have discovered the following:

1. The original CRT was a 21ALP4 (AW53-80). It has a neck length of 7.5”
2. The replacement 21DJP4 has a neck length of 5.5”. That's 50mm shorter!
3. The Philips yoke is encapsulated in an aluminium can and the centering magnets are outside the can. That puts them nearly 5” back from the CRT bulb.
4. When installed on the 21DJP4, the centering magnets are almost back at the tube's cathode, roughly where the ion trap would be if it was used. (The 21DJP4 is a later design that doesn't use an ion trap).

No wonder the centering magnets shade and defocus the beam!

There isn't a lot you can do about this, that I can see anyway. I've tried placing magnets around the outside of the yoke to no worthwhile effect.

TVs that will be affected by this are all 90 degree sets that use the Philips yoke. That's Philips and Kriesler.

HMV F series models will also be affected because they use a can for the yoke that moves the centering magnets back to a similar position. At least with the HMV you can lose the can.

Of course you may be lucky enough to have a tube that's design centre or an original 21ALP4 that's still good.

The pucture on my Philips is good.
It has a 5.5 neck ,so does my pye w102 and the w101 is 7.5 inches.
So imagine its only on TVs that had a crt replacement .

Pete

Hmmm sorry I had to read that a few times , ok the penny has dropped I understand. I will check out the other necks on the tellies