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FDP Forum / Fender Amps: Vintage (before 1985) / 1968 vibro champ help



Sep 8th, 2019 10:36 AM   Edit   Profile  

I know this is going to sound stupid, but I’m the proud owner of a heavily modified vibro champ. There are two knobs on the back—one is a pseudo master volume, and one is for negative feedback. It has been updated with cal’s and a grounded plug. There’s also a speaker out option. Here’s the rub—short of taking it to a repair shop, is there a way to find out if that speaker out is meant to be used with the in cab speaker and what ohm rating it might be at? I’m happy to post pics or whatnot if that might help.

Contributing Member

American Patriot

About as ordinary as you can get.
Sep 9th, 2019 10:56 AM   Edit   Profile  

I can't answer your question but I'd put that thing back to original layout.

Contributing Member

Whitehorse Canada

I don't get out much
Sep 9th, 2019 06:17 PM   Edit   Profile  

Stock speaker was 3.2 ohms.
Original speaker out jack was a non-switching RCA jack.
If the RCA jack is still present, the extra jack should, if wired correctly work with or without the stock speaker connected.
If the stock speaker output jack is not present, you will need to remove the chassis and determine whether or not the replacement jack (most likely 1/4" TS") is a switching jack.
If it's a switching jack, the original speaker....now with a 1/4" TS connector will have to be connected for the extra speaker out jack to function.
If that's the case, a dummy plug in the replaced speaker jack will permit you to use an external cab without using the internal speaker.
Here's where some care should be taken.....Original speaker is 3.2 ohms, if you connect another speaker, say a 4 ohm driver with the original speaker connected, you are now presenting a somewhere in the 2 ohm ballpark load to the output transformer.
I don't think it would be wise to do so.

If you have two speakers with different ohm ratings connected to the output of an amp, the speaker with the lowest ohm rating will be louder.
That's my understanding.
Please don't act solely on my advice, wait until one or more of the advanced techs chimes in.

FDP Forum / Fender Amps: Vintage (before 1985) / 1968 vibro champ help

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