TV sets with Magic-Eye Tuning Indicator?

[Maarten]

The bar was quite common for several chassis when fitted with VST tuning. I think on some sets, they changed colour whenever the AFT caught on.

[Synchrodyne]

Originally Posted by Synchrodyne

The German, Belgian and Finnish examples kindly listed by German Dalek evidently all used what might be called peak reading magic eyes. So the inference is that they derived the magic eye bias from rectifying vision carrier after it had been passed through a narrow band tuned circuit with a net peak (after correcting for the Nyquist slope) at the carrier frequency, as was also the apparent dominant approach in North American practice.

Well, perhaps not necessarily so. From the late 1940s there were developed various circuits that adapted a conventional peak reading magic eye so that it was polarity sensitive or null sensitive, and so could be used as a centre-zero type tuning indicator, fed from an FM (or AFC) discriminator. In some cases such circuits retained amplitude sensitivity, and a well-known example was found in the original version of the Leak Troughline FM tuner. Notwithstanding the 1947 American precedent of the 6AL7GT, “two-bar” magic eyes directly suitable for FM centre-zero use did not appear in Europe until later in the 1950s. So it is possible – although I suspect unlikely - that some of the TV receivers listed above did use vision AFC bias rather than rectified vision carrier to drive their magic eyes.

Originally Posted by Synchrodyne

Radio-Electronics 1968 January, page 42ff.

Not a magic eye, but the article described a new Westinghouse tuning indicator using on-screen bars. The circuit was driven by rectified narrow-band vision carrier.

I had another look at that one. It was in fact of the centre-zero type, with the moving bar being either side of a fixed centre bar according to the direction of the tuning offset. It used a slope detector. It might well have been the first of the on-screen bar type tuning indicators.


Cheers,