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FDP Forum / Fender Amps: Vintage (before 1985) / Vintage JBL polarity question



May 19th, 2016 04:42 PM   Edit   Profile  

Does anyone know if all the vintage JBL D120F gray frames from the mid to late 60's that came in the speaker cabinets had reverse polarity? Anyone know when JBL supposedly standardized this to be compliant with the rest of the industry? I've read that the Black terminal is suppose to be the positive terminal and Red is the negative. So did Fender connect the Black wire to the Black terminal and to the positive contact of the Jack in speaker cabs? I know how to test to tell which terminal is positive using a battery but that's not the issue. I've seen a lot of Fender amps with these D120F all wired differently. Some have the Black wire to the Red and some to the Black terminal.

(This message was last edited by roadhog96 at 07:35 PM, May 19th, 2016)



May 19th, 2016 05:32 PM   Edit   Profile  

Yes, all vintage JBL D131, D120, D130, D140 were all black positive and red negative. In a single speaker amp it really doesn't matter which way the cone moves.



May 19th, 2016 05:39 PM   Edit   Profile  

Isn't it customary to wire the JBL with the black wire in the speaker cab to the positive black terminal and then to the positive contact on the input Jack.

I have another question about the F plug on the back of the combo amp to the speaker. With speakers other than JBL, doesn't the black wire go to negative and white to positive? Isn't it just the opposite?

(This message was last edited by roadhog96 at 08:10 PM, May 19th, 2016)

Contributing Member

Eat. Sleep. Guitar.

May 20th, 2016 05:50 AM   Edit   Profile  

You can easily determine a speaker's polarity with a 9v battery.

Briefly (less than a second) touch the battery's terminals to the speaker's terminals.

If the cone moves forward, the battery's positive terminal is on the speaker's positive terminal.

If the cone moves backward, the battery's negative terminal is on the speaker's positive terminal.

This will not harm a guitar or bass speaker.

Steve Dallman
Contributing Member

Merrill, Wisconsin

Age is just a number...mine is big
May 27th, 2016 11:56 AM   Edit   Profile  

What Peegoo said. I have heard tales that JBL did this on purpose so if someone replaced a JBL with a "lesser brand" in a multiple speaker rig, and didn't know about JBL's reversed polarity, the rig would perform poorly due to the phase problems. Put a JBL back in, and no problems.



you want me to play where?
May 27th, 2016 12:32 PM   Edit   Profile  

Honestly, I check EVERY speaker I install because I have gotten them mis-marked in the past. It only happened once but once is enough. Now they ALL get checked. Mike



May 27th, 2016 12:54 PM   Edit   Profile  

What JBLTWIN1 said. Then there's the chance that any speaker that was re-coned could have its polarity reversed.

(This message was last edited by slider313 at 03:10 PM, May 27th, 2016)

FDP Forum / Fender Amps: Vintage (before 1985) / Vintage JBL polarity question

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