10-07-2017, 07:53 PM
(This post was last modified: 10-07-2017, 07:55 PM by ppppenguin.)
The whole business of live chassis sets was driven by low cost and, to a lesser extent, by reducing size. A mains transformer was an expensive and large component. In the earlier days, much less int he 1950s, there was also DC mains in many areas. So live chassis sets became common on both sides of the Atlantic. The valve makers made valves suitable for series chain operation, something that was easier for 115V mains than 240V. Again no set designer really wanted a big, hot dropper resistor and in the 1950s a dropper capacitor would have been large and expensive. For HT, life was easier here, as rectified 115V was a rather low voltage unless you were using valves designed for battery sets.
As Trevor has said, line cord was a horrible but cheap way to drop the voltage. Complete with asbestos to add to the hazards.
In some countries, such as Australia, live chassis was rare. Was it illegal there? In the UK at least it was absolutely standard in TVs for several decades. A TV would need a big mains transformer and the magentic field could affect the picture. The Thorn 2000 I'm working on is a rare exception. It has a hefty mains transformer carefully designed to have low external magnetic field. Heavy and expensive but the only viable way in 1967 for a solid state colour set.
Safety regulations tend to play "catch up" rather than being ahead of new products. And manufacturers will always be tempted to do the bare minimum to comply. Even as late as the 1960s "Which" magazine was reporting TVs that barely met the accessibility requirements for live chassis operation. Now of course we have widespread infringement of the CE marking rules. Notably on phone chargers.
Plus ça change, plus c'est la même chose
PS: I thought the term"widow makers" was used of early TVs with mains derived EHT. Truly lethal to service techs.
As Trevor has said, line cord was a horrible but cheap way to drop the voltage. Complete with asbestos to add to the hazards.
In some countries, such as Australia, live chassis was rare. Was it illegal there? In the UK at least it was absolutely standard in TVs for several decades. A TV would need a big mains transformer and the magentic field could affect the picture. The Thorn 2000 I'm working on is a rare exception. It has a hefty mains transformer carefully designed to have low external magnetic field. Heavy and expensive but the only viable way in 1967 for a solid state colour set.
Safety regulations tend to play "catch up" rather than being ahead of new products. And manufacturers will always be tempted to do the bare minimum to comply. Even as late as the 1960s "Which" magazine was reporting TVs that barely met the accessibility requirements for live chassis operation. Now of course we have widespread infringement of the CE marking rules. Notably on phone chargers.
Plus ça change, plus c'est la même chose
PS: I thought the term"widow makers" was used of early TVs with mains derived EHT. Truly lethal to service techs.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
