Bench Testing Positive Ground AM Radio

65blkbkgt · 22nd February 2008, 02:34 PM

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 · 22nd February 2008, 02:47 PM

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 · 22nd February 2008, 03:26 PM

Thanks for your reply and info.!

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

I Am An Idiot · 24th February 2008, 05:16 AM

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 · 24th February 2008, 05:57 AM

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

jol50 · 24th February 2008, 03:07 PM

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

cliffforrest · 24th February 2008, 03:55 PM

Quote:

Originally posted by jol50
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 · 24th February 2008, 06:13 PM

Quote:

Originally posted by cliff

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 · 24th February 2008, 06:43 PM

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 · 24th February 2008, 07:09 PM

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.

22nd February 2008, 02:34 PM	#1
65blkbkgt diyAudio Member Join Date: Jun 2007	Bench Testing Positive Ground AM Radio 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

24th February 2008, 05:16 AM	#4
I Am An Idiot diyAudio Member Join Date: Mar 2007	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. __________________ If it ain't broke Don't fix it

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22nd February 2008, 02:47 PM	#2
jol50 diyAudio Member Join Date: Nov 2007	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.

22nd February 2008, 03:26 PM	#3
65blkbkgt diyAudio Member Join Date: Jun 2007	Thanks for your reply and info.! Does that mean that the positive from the power supply isn't connected?

24th February 2008, 05:57 AM	#5
65blkbkgt diyAudio Member Join Date: Jun 2007	Now that sounds about right. I appreciate your information (especially about the fuse!). Thanks!

24th February 2008, 03:07 PM	#6
jol50 diyAudio Member Join Date: Nov 2007	Also make sure your bench or anything the radio could touch is not grounded.

24th February 2008, 06:43 PM	#9
cliffforrest diyAudio Member Join Date: Sep 2004 Location: UK	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.

24th February 2008, 07:09 PM	#10
65blkbkgt diyAudio Member Join Date: Jun 2007	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.