Newbie's First Questions RCA TS 721 Restoration

[Chris K]

Yep...I just bought one off ebay. They are pretty cheap!

[Notimetolooz]

I was away doing other things and missed a lot of the conversation.

This is what a permanent magnet single ion trap looks like from the 1950s.
[ATTACH]

Some early CRTs needed double ion traps.

The design of the electron gun in the CRT determines what type and whether an ion trap is needed. In a nutshell the guns are designed to send the beam out in a way that it does not reach the screen. Either the beam hits the side of the CRT neck or some internal structure in the gun. That because the beam contains ions that are heavy and would damage the screen over time. The ion trap acts on the electrons and redirects them to hit the screen.

[old_coot88]

The bent gun shoots both electrons and ions off to one side. Electrons have very little mass compared to ions, so the "trap" is actually a beam-straightener for electrons. The the ions, being much heavier, remain trapped while the electron beam is re-directed down the axis of the tube. It's analogous to winnowing wheat in the wind; the grain as it falls is much heavier than the chaff, so the grain is "trapped" while the chaff gets blown away.

[Chris K]

So here's a picture of what the trap on my 721 looks like and where I positioned it for the brightest picture...and an additional photo of it on my bench.

[Notimetolooz]

Yes, that is a early type of permanent magnet ion trap. I've seen pictures. Sometimes those are hard to remove, there was a thread that involved that problem.

Are you aware of the "Search" feature on the forum? It may help you avoid the mistakes others might have made. There are several threads involving the 721.

Zenith liked to call ion traps "beam benders" which is more descriptive.

[Chris K]

Thanks! Pattern generator on its way and it looks like it's arriving today. Nothing special but the price was right ($10) and there are pictures of it working.

[Notimetolooz]

That seems good enough.
Some generators put out other patterns that are more useful when looking at the signals with a scope.
If you can, try the generator with another working TV, some flat screens can receive the analog channels. I don't know if the kinks at the intersections are due to the generator or that TV. Flat screen sets do not have this type of distortion.

[Yamamaya42]

Originally Posted by Chris K

Thanks! Pattern generator on its way and it looks like it's arriving today. Nothing special but the price was right ($10) and there are pictures of it working.

I have the same unit, my dad built it long ago, it does an... adequate job, not one of the best ones by far! It has it's odd quirks.
I need to replace the filter caps in mine because it has started to develop a sort of hula effect to it's output! :O