How Come Early CRTs contained more Ions?

[jr_tech]

Originally Posted by Tubejunke

Just follow the instructions in any good old manual and everything will come out fine. Old TV manuals show up a lot in Goodwill stores with bookshops in them.

The best advice I could give anyone here that is new to the ion trap is: if you remove one, mark an arrow pointing toward the faceplate of the crt. This is so the polarity of the magnetic field will not be reversed. Take a FINE sharpie and just trace the positioning of the magnet on the glass of the crt neck. Then take a telescopic look down the gun and take note of the clock positioning of the magnet. This way you can't go wrong.

Now it's a whole different story when you run into a situation where the magnet has been disturbed and is out of place or missing. Maybe we could make another thread out of that.

This is good advice, the trap alignment *procedures* in these old manuals are usually quite correct. Proper alignment of the magnet is important for several reasons, and the life of the tube can be shortened if it is not done correctly. Some stated reasons for proper adjustment:

1. Less than optimum beam current (magnet not adjusted for max brightness) means that the brightness control must be turned up higher than necessary, which can lead to premature cathode failure. This is my primary concern when adjusting the magnet.

2. Spot size/beam characteristics may suffer if the magnet is not adjusted properly. Best efficiency usually produces the sharpest picture.

3. It is possible to deposit metal from the anode to the screen if the magnet is not adjusted properly.

4. Ions can strike the screen if the magnet is not adjusted properly. No, I really don't believe this can happen, because the trap magnet is simply not strong enough to bend the ion "beam" enough to travel straight down the gun.

In many old sets that I have seen, it is very difficult to obtain "perfect" adjustment, due to a variety of conditions, such as weakened position magnets, magnetized yoke support and other nearby chassis pieces, non-uniform focus magnet field, and perhaps a few other problems. The inability to adjust the magnet to obtain max brightness without neck shadow or positioning problems indicates that "something is wrong" that can perhaps be remedied. I will try to correct any of these problems first. If I *must*, I will slightly mis-adjust the ion magnet or place a small permanent near the neck of the tube to correct the problem, and not worry about it...much.

jr