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Old 12th Oct 2019, 1:06 pm   #20
Argus25
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Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
Default Re: Cretinous idea - The combined volume pot and mains SW.

Quote:
Originally Posted by GrimJosef View Post
Another advantage, which applies more in some situations than others, is that by forcing the volume to zero before disconnecting the power the switch-off click/thump can be limited to that which gets into the circuitry after the pot. This can be handy in hifi systems with high power amp stages.
This is an analogy of a much more important scenario.

In a TV set, when it is turned off, the scan collapses. This can result in a phosphor burn in the center of the CRT where the beam current gets concentrated, because EHT is still present and the beam current is still significant due to cathode emission. This can damage the phosphor.

Even in popular culture, there was the notion of the white dot in the center of the TV screen, after you turn off the TV set has some meaning.

This has even been the subject of comedy. Take the TV series "The Young Ones". Somebody asked..... that white dot in the center of the screen...what does it mean ? Neil replied: "It means something really heavy, it means there is no more TV"

So if there was ever a case where a rotary control should be connected with an on-off power switch, it would be to put the power switch on the CRT's brightness control, in a TV, so it was zero when the set was switched off to suppress the white spot.

Of course designers wised up to this, and in better designs had "spot killers" that take the CRT's grid very negative at turn off, to prevent the white spot and phosphor burn, regardless of the angular position of the brightness control.
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