[morzh]

   

Rod


Here's what I think is there:

1. Two-prong plug:

Normally you would have your switch on the "Live" wire and the "Neutral" is the one permanently connected.
- With the caps in front of the switch, upon plug-in the caps connected in series will charge to the whatever voltage there is at the moment of unplugging, as the chassis is insulated. So you have 7.5nF charged to up to potentially 170V.
- With caps after the switch they will fully discharge via the load, uf the radio is hot or vial sheer DC resistance of the primary if cold (plug-unplug). So no danger here, but there is another problem - every time you make the switch you create a spark and this will eat the metal out eventually; I think this was one of the thoughts behind having the switch after the caps, as the transformer when the radio is cold is simply an inductance and should not create sparks, and when it is the break, then the transformer looks like DC resistance and also should not spark too badly.

2. 3-prong plug:

Same thing pretty much, only the lower cap never charges much due to the Neutral and Chassis being under the same potential, and the charge kept by the cap is twice as large (15nF vs 7.5nF) and the energy is 4 times, so the pinch will be more painful.


So to have the benefit of not sparking and not having charged caps the switch is better off being where it is now, and a 1mOhm resistor will discharge the caps in 7.5ms.



There is nothing wrong with the caps plugged all the time. These caps in the pic are Y2-rated (or they should be) and so fail open. If X-cap is used (why?) then there should be a fuse in series, as X-cap is not guaranteed too fail open.


And you are right, there is no comp[lete circuit, and this is why without bleed resistor you could get a little shock.