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Appliance power switch in neutral line - legal in aus?

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vk6zgo:

--- Quote from: james_s on March 10, 2021, 02:09:55 am ---
--- Quote from: vk6zgo on March 10, 2021, 01:54:52 am ---When a dial lamp burnt out, it normally went open circuit, so I fail to see how that could affect the life of the rectifier tube in such a design.
If the insulation failed, maybe that would do it.

--- End quote ---

IIRC the bulb was wired in parallel with a tapped segment of the tube heater, so if the bulb burns out the voltage across that segment rises due to the higher resistance. This causes that part of the heater to run hotter and burn out.

--- End quote ---

OK, it seems that in Oz, we did a lot of things differently.
Radios were quite a lot more expensive, so less drive to go cheap.

The tube factories ramped up during WW2, concentrating upon 6v heater tubes, so were reluctant to start making series string types in the postwar period.
On top of that, we had the problems of a higher supply voltage compared to the USA, so would have needed to produce tubes for some exotic heater voltages & use barreters, or big series resistors, like the UK & Europe.

It was just easier to go with power transformers, allowing fullwave rectification, easier HT filtering, higher HT for greater output stage efficiency, & a "cold chassis", removing the necessity of a lot of the extra insulation necessary on "hot chassis" designs.

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