Line capacitors - Printable Version

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Line capacitors - 45philcodon - 07-02-2019

Most Philco radios have a capacitor from each side of the line to chassis ground. I understand the usefulness of a capacitor from chassis ground and the neutral side of the line thereby eliminating the need for an external connection to ground.
What is the purpose of the capacitor from the other side of the line to ground? It seems like a minor shock hazard in that the chassis would float at approximately 1/2 of line voltage.
Please explain if both capacitors are needed and why.

Thank you,

Don

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RE: Line capacitors - morzh - 07-02-2019

Since the plugs of old were not polarized you could plug your cap-decoupled line into either L or N. In which case your float would be either 0V or full 117V to GND.

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RE: Line capacitors - vacuum - 07-04-2019

RE in the case connecting with float being full line voltage... Good point!

I have seen two instances where 6-Vac dial, or power-on lights, popped mysteriously. Likely from a transient when connecting the ground lead of a modern 3-wire-grounded test instrument to an older 2-wire 120-V device. In each of those instances, one leg of the 6.3-V filament winding (and the lamp) were grounded to the chassis. In one case, device and test instrument were connected to a shop circuit containing a GFCI. As soon as the ground lead of new instrument touched old chassis, it popped the GFCI (and bulb!). I have found it useful to install 3-wire plug to older devices. to fix the chassis at earth; each leg of the primary power transformer is then 60-Vac from earth.
Cheers. John

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