Bench Testing Positive Ground AM Radio

[65blkbkgt]

Hi Guys,

I picked up an old '40's am radio that is positive ground. I've never tested a positive ground radio. If negative ground radios ground to the chassis of the radio what does the positive ground radio ground too?

Thanks for your help!
Steve

 

[jol50]

As I recall the positive is ground instead. So you power it with the negative and the whole case is positive compared to modern ones.

 

[65blkbkgt]

Thanks for your reply and info.!

Does that mean that the positive from the power supply isn't connected?

 

[I Am An Idiot]

The positive of your power supply connects to the chassis of the radio. And connect the wire of the radio to the negative terminal of the power supply. To be safe, remember to put a 5 amp fuse in either wire.

 

[65blkbkgt]

Now that sounds about right. I appreciate your information (especially about the fuse!). Thanks!

 

[jol50]

Also make sure your bench or anything the radio could touch is not grounded.

 

[cliffforrest]

Why?

Also make sure your bench or anything the radio could touch is not grounded.

The radio chassis will be grounded, and powered from the negative side of the supply.

There is no need to worry about isolation.

Perhaps you are thinking of a situation using a supply with the negative already grounded? Or putting the radio in a vehicle with a negative ground battery? THEN you will have problems!

 

[65blkbkgt]

Re: Why?

The radio chassis will be grounded, and powered from the negative side of the supply.

There is no need to worry about isolation.

Perhaps you are thinking of a situation using a supply with the negative already grounded? Or putting the radio in a vehicle with a negative ground battery? THEN you will have problems!

See that's what I'm not sure of. Whether or not the cars back then had negative or positive ground batteries. I almost want to say that being a positive ground radio the battery would almost have to be positive ground?

Anyway.....so I think I have this straight (hopefully). Neg of power supply to power wire w/inline fuse, pos of power supply to chassis, power up and close my eyes.

 

[cliffforrest]

Yes, you've got it all right.

A long time ago cars were mostly Postive earth - but not all.

'caused havoc trying to fit any electronics!


There is nothing magic about "earth" or "ground".

Any circuit will quite happily work without any ground connection, just + to + and - to -.

However when connecting 2 or more things together, and for electrical safety, it becomes important.

 

[65blkbkgt]

Ooooh. I've got it now.

Thus the invention of the three pronged plug so my house doesn't burn down. Makes sense to me.

I really appreciate your help!

I would imagine there were more '20's and '30's cars with pos. ground than since.

 

[jnb]

With something this old, surely you'd want to open it up and inspect the components and judge the circuitry for viability. While you're there, you'd learn the ground scheme.

 

[gmphadte]

cliff wrote

However when connecting 2 or more things together, and for electrical safety, it becomes important.

This issue will be solved if u use separate battery for the positive grounded device.

Gajanan Phadte