On Wednesday, August 2, 2017 at 6:05:49 PM UTC-4, wrote:
I want to know what is wrong with using a five buck transformer rather than creating a shock hazard.

Such a scheme beats on the cap and it may go bad. In fact it may short out and teach you why they do not do this. Hopefully your fire insurance is paid up.

This is worse than those little transformerless cellphone chargers. They should not be allowed to sell those things.

There is a right way and a wrong way, and a capacitively coupled doodad like this is the wrong way.



Yes, but I believe it was only an exercise in a class. But you can use this technique on the secondary of a transformer instead of using a dropping resistor, although I can't recall seeing it done.

The only time I used it was very recently on an old AC/DC radio from the 30s that had about 80V worth of filaments but needed to run on 120V. The radio originally used a resistive AC cord which consisted of two normal conductors and one length of asbestos yarn wrapped in a spiral of nichrome wire that ran the entire length of the AC cord and connected to one side of the AC plug. This long wire resistor provided the necessary drop for the filament requirement. The cord was shot so I put in a two wire cord and used something like 6uf worth of film caps out of Panasonic plasma sustain to get down to the proper voltage for the tube's series string. It's fused, but it's a temporary solution just to get the radio operational. If I ever restore the radio I'll probably locate a replacement cord as there's no room for a dropping resistor of the necessary wattage in the case (miniature mantle radio).