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Radio GE Superadio 7-2887A query

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Doz
 Doz
(@doz)
Noble Member
Topic starter
 

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? 

 

Screenshot from 2021 05 15 11 20 55

Thanks in advance for your wisdom!

 
Posted : 15/05/2021 10:26 am
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Nuvistor
(@nuvistor)
Illustrious Member
 

@doz

I dont know the reason only guesses but I would leave it out.

 
Posted : 15/05/2021 1:54 pm
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Doz
 Doz
(@doz)
Noble Member
Topic starter
 

@nuvistor That's my feeling too! 

 

Out it comes.

 
Posted : 15/05/2021 2:21 pm
PYE625
(@pye625)
Illustrious Member
 

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.

 
Posted : 15/05/2021 2:37 pm
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PYE625
(@pye625)
Illustrious Member
 

A capacitor would be better suited for that rather than a resistor I would have thought though.

 
Posted : 15/05/2021 3:29 pm
Doz, Doz and Doz reacted
turretslug
(@turretslug)
Honorable Member
 

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.

 
Posted : 16/05/2021 2:45 pm
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PYE625
(@pye625)
Illustrious Member
 

Makes sense.

 
Posted : 16/05/2021 3:09 pm