Single Gun Color CRT

[jpdylon]

single gun that early? wow. So is that the "apple" design?

That would be something that the ETF would own or want to own methinks.

[old_tv_nut]

Originally Posted by jpdylon

single gun that early? wow. So is that the "apple" design?

That would be something that the ETF would own or want to own methinks.

NOT the Apple design.

This was a shadow mask tube that had what I would describe as dynamic modulation of the purity settings, so a single beam was moved sequentially to the correct position for red, green, and blue. It was probably MORE touchy for adjustment than a 3-gun tube. For "dot-sequential" color (the RCA system), the beam angle of arrival would be centered on the three RGB phosphors for monochrome, and decentered in the direction and amount indicated by the phase and amplitude of the color difference. This sounds like a real mess, since getting the correct brightness and ratio of RGB simultaneously would depend on whether the phosphor dots continuously covered the screen. If they had any non-emitting space between them, the brightness would drop as soon as you moved the beam arrival angle off-center.

[jhalphen]

Hello to all,

To answer VintageCollect's comment about perfect convergence on single-gun color tubes, here is a picture of the familiar convergence pattern on the screen of a Sony Indextron.

This is a 625 line pattern fed through a digital standards converter to produce 525/60 then broadcast by an NTSC transmitter.

Also, color bars on the same beast.

Best Regards

jhalphen

[old_tv_nut]

With the Indextron, (or the early "Apple" tube) you should get no convergence error, because there is only one beam emanating from a constant position. The RCA tube, however, moves the apparent point of emission, so its beam is going through a different part of the deflection yoke aperture depending on the color selected. In this case, all bets are off. You have essentially turned one beam into three sequentially. You need specifically to design so the beam hits the same spot on the screen no matter what the color-selection field is doing.

By the way, even a field-sequential set can show "convergence" errors if the high voltage and sweep are not perfectly stable from field to field. We could see this on the "personal viewer" color wheel at ETF when the contrast was turned up too high on the DuMont set, causing alternate fields to have different scan widths.

[vintagecollect]

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