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what is the speaker Ohm rating for a stock 57 AM radio (non-push button) If I use two speakers do I split or double that? for 4 speakers?
 

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As I understand it, the push button radios used a 4 OHM speaker and the manual tune used a 8 OHM speaker. Someone else needs to confrim this, but I think if you run the speakers parallel (positive to positive/ negative to negative) they remain 4 OHMS and if you put them in series (positive wire to positive on the first speaker, negative from the speaker to positive on the second speaker and the negative on the second speaker to the negative speaker wire) you double the resistance. In series is bad. It will cause the radio to over heat and fail.
But PLEASE double check what I think I know before trying this.

The short of this is if you use one speaker on the manual tune, use a 8 OHM speaker.
 

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two 4 ohm speakers in series = 8 ohms
two 4 ohm spekers in parallel = 2 ohms

two 4 ohm speakers in parallel that are in series with another pair of
4 ohm speakers in parallel = 4 ohms.

The stock 50s radios used an output transformer similar to a stepdown transformer in a welder .... thousands of ohms stepped down to either 4 or 8 ohms.

Its usually better to be off in the higher direction..... 8 ohm speaker / 4 ohm radio vs a 8 ohm radio into a 4 ohm speaker.
higher resistance means less current out of the radio. You can always add a series resistor in the line between the radio and the speaker.

That's what we did in the 60's. They made a high power fader that you could add between a radio and two speakers..... the radio was attached to the center terminal and the two speakers attached to either end. Moving the knob counterclockwise moved the center wiper closer to one speaker and father away from the other making the sound "fade" from the front to the back. In the center position, there was 4 ohms resistance in series with each 4 ohm speaker making each leg 8 ohms.

Since the two sides were in parallel, the overall resistance was back at 4 ohms again.

That will still work if you can find the parts. It might be better to install a four-way amp if you are looking for high fidelity.
 
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