NotTaR of Television Sets : Tony's notes on setting convergence on d..  
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Tony's notes on setting convergence on delta gun CRTs

(This section from: ard12@eng.cam.ac.uk (A.R. Duell))

The older delta-gun tubes (3 guns in a triangle, not in a line) can give **excellent** pictures, with very good convergence, provided:

  1. You've set those 20-or-so presets correctly - a right pain as they interact to some extent.

  2. The CRT is set up in the final position - this type of tube is more sensitive to external fields than the PIL type.

Both my delta-gun sets (a B&O 3200 chassis and a Barco CDCT2/51) have very clearly set out and labeled convergence panels, and you don't need a service manual to do them. The instructions in the Barco manual are something like:

"Apply crosshatch, and adjust the controls on the convergence board in the numbered order to converge the picture. The diagrams by each control show the effect".

Here's a very quick guide to delta gun convergence where the settings are done using various adjustments on the neck of the CRT (if you don't have a service manual but do know what each control does, and where they all are - otherwise, follow the instructions in the service manual --- sam):

  1. Apply a white crosshatch or dot pattern to the set. Don't try and converge on anything else - you'll go insane. It's useful to be able to switch between those 2 patterns.

  2. Before you start, set the height, width, linearity, pincushion, etc. They will interact with the convergence. Also check PSU voltages, and the EHT voltage if it's adjustable. That's where you do need a service manual, I guess.

  3. Turn off the blue gun using the A1 switch, and use the red and green static radial controls to get a yellow crosshatch in the middle of the screen. These controls may be electrical presets, or may be movable magnets on the radial convergence yoke (the Y-shaped think behind the deflection yoke).

  4. Turn on the blue gun and use the 2 blue static controls (radial and lateral) to align the blue and yellow crosshatches at the center of the screen. Some manufacturers recommend turning off the green gun when doing this, and aligning red with blue (using ONLY the blue controls, of course), but I prefer to align blue with yellow, as it gives a check on the overall convergence of the tube.

  5. Turn off the blue gun again. Now the fun starts - dynamic convergence. The first adjustments align the red and green crosshatches near the edges - I normally do the top and bottom first. There will be 2 controls for this, either a top and a bottom, or a shift and a linearity. The second type is a PAIN to do, as it's not uncommon for it to affect the static convergence.

  6. Getting the red and green verticals aligned near the edges is a similar process.

  7. You now have (hopefully) a yellow crosshatch over the entire screen.

  8. Now to align the blue. This is a lot worse, although the principle is the same. Turn on the blue gun again, and check the static (center) convergence

  9. To align the blue lines with the yellow ones, you'll find not only shift controls, but also slope controls. Use the shift controls to align the centers of the lines and the slope controls to get the endpoints right. These interact to some extent. You'll need to fiddle with the controls for a bit to work out what they do, even if you have the manual.

The convergence over the entire screen should now be good....

A word of warning here... The purity is set by ring magnets on almost all colour CRTs, but on PIL tubes, there are other ring magnets as well - like static convergence. Make sure you know what you are adjusting.

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