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|NotTaR of Television Sets : Tony's notes on setting convergence on d..
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The older delta-gun tubes (3 guns in a triangle, not in a line) can give
**excellent** pictures, with very good convergence, provided:
- You've set those 20-or-so presets correctly - a right pain as they
interact to some extent.
- 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
"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):
- 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.
- 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
- 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
- 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.
- 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
- Getting the red and green verticals aligned near the edges is a
- You now have (hopefully) a yellow crosshatch over the entire screen.
- 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)
- 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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