Colour CRT · 1970s in-line tubeInside the Picture Tube

Three electron guns, one steel mask, and a beam that paints 625 lines 25 times a second. Colour sets of the era, such as Philips models built around its 20AX tube, put their three guns side by side like this. Slow time down to watch the beam draw the picture.

Power

Switch off to see the picture collapse to a dot. Sound adds the 15.6 kHz line whine and the degauss thunk.

Play

With the magnet on, drag across the screen. The field bends the beams and they strike the wrong phosphor stripes. The steel mask stays magnetised afterwards until you degauss. Electrons have no colour: the beam tint only shows which gun they came from.

Time

Slow motion

Picture

Brightness

Contrast

Colour

Tube

Anode (EHT)

Focus

Afterglow

Fewer lines make the zig-zag scan and interlace easy to see. Real P22 phosphor fades in about a millisecond, so in slow motion only a narrow band stays lit, just like high-speed camera footage.

Sync

V-hold

H-hold

Push a hold knob past its lock range and the timebase stops following the sync pulses. The picture rolls or tears into diagonal bars.

Video signal · this line

composite video (sync, then luminance)horizontal yoke current

Through one slot

A cross-section at the beam's landing spot. Each beam is wider than a slot; most electrons hit the steel. The ones that get through arrive at a slightly different angle per gun, so each can only reach its own colour of phosphor.