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In Reply to: Thoughts on doubler supply straight out of wall no transformer 450V caps.??? posted by -3db on September 16, 2002 at 00:55:06:
Guess what happens if the power plug (or the wall socket) is reversed? The chassis goes live, everthing connected to an interconnect or speaker wire goes to full line voltage, and zap, you're dead.
And don't kid yourself that wall sockets are always correctly wired - get a Radio Shack or Home Depot safety tester and discover for yourself how many sockets have neutral and hot reversed. Just because it violates every electrical code doesn't mean that electricians don't make mistakes. I've even measured *ground* miswired!
Follow Ups:
Lynn,Your point about miswired outlets is well taken. It's a good idea to check outlets all the time.
The type of B+ supply mentioned was used in low cost table radios with bakelite cases. A series heater string was used, allowing cheap transformerless construction. My father had such a radio that used a 117Z6 as the voltage doubler.
IF (very big if) the wall outlet has been wired properly, a RELATIVELY safe P/S can be built. Connect the safety ground wire to the metal chassis. Build the "classic" full wave doubler with a 117Z6 or a pair of damper diodes. Wire the "hot" lead to the center of the filter capacitor stack. Wire the "neutral" lead to the 2 discrete diodes, then wire the diodes to the ends of the filter capacitor stack. SS diodes are out, since they have high pulse current capability. Current, not voltage, kills; therefore, proper fusing of the "hot" line as it connects to the filter capacitor stack is ESSENTIAL. A DPDT switch that interupts both the "hot" and "neutral" leads should be used too.
Of course, isolation from the AC mains by transformer is THE WAY TO GO.
> The chassis goes live, everthing connected to an interconnect or speaker wire goes to full line voltage, and zap, you're dead <Exactly - but maybe it's not the culprit who dies (he could deserve it) but it could a child - his or a neighbours!
Not smart...
Allen
With a voltage doubler, your signal ground will be about 150vDC negative relative to safety ground. Anything plugged into this (CD player, TV, etc) will then be at -150vDC relative to anything connected to earth ground (water pipes, damp boards, all other electrical appliances, etc.) DC is generally regarded as more dangerous than AC, because the muscles are frozen and you can't jerk away - you just cook like a hot dog.
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