radio polarity

[bullno]

Novice Bruce again with radio question. Still a long way from finishing my restoration (drop motor in last weekend, hope to see if I can get it to start this weekend). When I bought the car it had two radios along with most everything else in boxes. Plan on keeping the car positive ground and can anyone tell me how to check to see if either radio is positive ground. Don't want to mess them up if they are working. thanks Bruce

 

[spritenut]

If it is not a BMC,or Radiomobil radio it is most likely negative ground.
If it has FM or a tape player, it surely is neg ground.
If you really want to use it and it's neg ground, it will work if you hook it up backwards, I mean positive to the red wire and negative to the radio chassis but you will have to isolate the radio from touching ground.
This also means isolating the antenna from ground.
Or see if Radioshack still has those +/- converters we used to buy back in the 70s so we could have out 8 track players in our positive ground cars.

 

[John Kuzman]

Bruce -

If the radio is negative ground and you want to keep the car positive ground, antique radio folks use power inverters.

https://www.radiosforoldcars.com/power.htm

I installed one in my big Healey over seven years ago, and it still works fine. Hey Frank, could that be due to the fact that it is Made in USA?

 

[Deleted member 8987]

The trick is the antenna.
The sheild usually is ground from the antenna mount.


I have positive ground, US made radios here.
No, not necessarily Brit only, but no tape decks.

 

[glemon]

Hard to tell just from looking, some older radios also had a polarity switch, I swear, though the memory is fuzzy, that the old BMC factory radios that were made for positive ground would work on negative as well, but I wouldm't plug one in and try it today.

If they look like they are late sixties or beyond vintage, or there is a manufacture date past those dates it is almost undoubtedly negative ground, if it was built before that, as previously stated, unless British it is still most likely negative ground.

 

[Deleted member 8987]

If they are vacuum tube with a vibrator tube, generally they are non-specific on polarity.


The radion in my Grandad's MK1 Jag was vacuum tube, and made no difference when he reversed the battery.

Funny, the head was in the pooka in front of the steering column, the body was under the driver's seat.

 

[Sarastro]

Vibrator power supplies should not be polarity sensitive, but I think you'll have trouble finding them these days, or at least finding one working. Some vacuum-tube radios can be set to either positive or negative ground with a little rewiring. A Blaupunkt I worked on recently had this feature; it also could be converted for 6V operation.

However, in my opinion, adding a radio is a good point to think seriously about converting to negative ground. If you start adding electronics, it gets progressively more difficult to find everything you need in positive-ground form. You don't want to find yourself in a situation where you've put a lot of time and money into positive-ground hardware, then want to add something that simply doesn't exist in that form.

And, yes, if it's not a vacuum-tube radio, it's almost certainly negative ground.

Also, if you do keep the positive ground and want to use a negative-ground radio, trying to insulate it from the auto's ground is likely to cause all kinds of problems. Better to use an isolator.