Wednesday, 10 April 2013

Yoke testing

I had a bunch of old Philips moulded yokes hanging around and decided to see if swapping through them on my modified Blaupunkt would make any different to the image quality. I'd been meaning to do this for ages so I could ditch some of these spare yokes. Today I finally got around to it...

Collection of Philips yokes
Underside of the yokes
I tested each yoke by comparing the "Dot Cloth" test pattern in the Street Fighter II test mode. The geometry wasn't adjusted for each test. I simply unplugged the yoke wires and neckboard before unscrewing the clamp and swapping yokes.

Yoke 1
Yoke 2
Yoke 3
Yoke 4
Yoke 5
As you can see, there really wasn't any noticeable difference between the first 4 yokes. The fifth yoke must have been taken from a Loewe CT1170. The yokes from these more modern darker tubes are incompatible with the earlier Philips tubes used in the CUC 5xxx era Grundig TVs hence the need for a yoke swap in the first place. In the fifth picture the image is compressed vertically and expanded horizontally because of the yoke/chassis mismatch. The vertical compression can be adjusted out but the horizontal expansion can't be.

The only difference I noticed between the first four yokes was the convergence in the corners of the image. None was really better than the others: all were imperfect with slight mis-convergence in the corners.

I guess this experiment didn't really yield any benefits: I ended up sticking with the original yoke I had in there. However, at least now I know. Sometimes the itch of curiosity just needs to be scratched.

Finally, even with the slight imperfections, the TV looks pretty damn good in game!

The Last Blade2


  1. Purity/convergence on Philips tubes is done through a non-adjustable magnetic ring inside the tube itself so even if you swap yokes the convergence remains the same.

    When talking about yokes you should mention the tube code (in particular the last two digits (e.g. 01 or 11). It doesn't make sense to say "yoke X was used with chassis Y" as TV manufacturers often use the same chassis on different tubes with variants to the chassis in order to account for the yoke differences.

  2. Thanks, MKL! Very good info!