Radio GE Superadio 7-2887A query
My earstwhile boss gave me this, and I'm just changing the transformer to enable it to work on 240V... but I have a question...
The supply is simplicity itself. Just a transformer and a full wave rectifier. But what is that 2.2Meg resistor doing between one side of the line and the chassis ground? Providing some sort of earth return for medium wave? Should I leave it, and connect it to the neutral side or remove it?
Thanks in advance for your wisdom!
It was probably to assist signal coupling to ground without a direct earth connection, but a proper earth would be safer. Can't say I have ever seen such an arrangement before though.
A capacitor would be better suited for that rather than a resistor I would have thought though.
I think (and I stand to be corrected) that this is a feature to limit and leak static charge acquisition from the hey-day of plastic cases, synthetic carpets etc. with two-wire mains cords, preventing snap-crackle-pop with audio devices and spurious operation of logic-dependent things. I've seen it in quite a few older Continental/Japanese electronics with double-insulated PSU arrangements and the resistor can be anything between 2.2 and 10 Megs. It goes without saying (pretty much) that any replacement should be a high-voltage type commensurate with double-insulation expectations, i.e. at least of VR37 rating and VR68 would be cheap insurance for peace of mind. I expect that Sideband will be better versed in this aspect than I am.
As said, if in doubt, leave it out, but beware of the possiblity of static-type effects.