Ampeg Jet-12D extension cabinet connection doesn't work.

Darnit

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I have a late 60's Ampeg Jet 12-D that has an extension cabinet jack which doesn't work.

It has 2 resistors across the connector lugs. With a jack plugged into the ext connector the in cabinet speaker works but the ext doesn't.
The ext cab speaker is good and properly rated (8 Ohm). The jack is a typical female TS connector. I've been searching for the purpose of these resistors but I haven't found any discussion about them. Lots of discussion of the jack types and wiring to shut off the in-cab speaker when an extension is hooked up but no resistors discussed except as a load simulation but these are way too small I think.

I tried to post a couple of pics but no joy. This is my first post so maybe I am 'suspicious'?
TIA for any help
don
 

corliss1

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Could you post the schematic that matches the version of the amp you're looking at?
 

Peegoo

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That ext jack may have been modified (resistors added) to make it a 'line out' jack. If that jack is not providing enough voltage to drive a speaker, try running an instrument cable from the jack to the input of another amp.

IMPORTANT NOTE: this can cause damage to the second amp's preamp if that jack is putting out a speaker-level signal! Be careful!
 

Darnit

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That ext jack may have been modified (resistors added) to make it a 'line out' jack. If that jack is not providing enough voltage to drive a speaker, try running an instrument cable from the jack to the input of another amp.

IMPORTANT NOTE: this can cause damage to the second amp's preamp if that jack is putting out a speaker-level signal! Be careful!
thanks for the reply, Pee.

After reading the interweb, I decided the resistors were an extra feature and deleted them with the hot wrench. . . in this case a soldering iron. This resulted, not only in a working ext cab output but an overall gain of about 1/4 volume and much better tone and 'balls' ..

It is a very sweet amp made even sweeter by the addition of a Gallien-Krueger open back 12" Celestion extension cab. This cab has about a 20-30 degree slant back design and placing them apart results in a psuedo-stereo kind of sound (I'll have to check to make sure the speakers are in phase - lol).

I appreciate everyones help - it prolly was a line-out mod but we'll never know and I don't care!
Cheers,
_don
 

Peegoo

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I appreciate everyones help - it prolly was a line-out mod but we'll never know and I don't care!
Cheers,
_don

Here's what a line-out mod usually looks like...this application fits into a small box that can be used with any amp's extension speaker. IMPORTANT: you must leave the amp's speaker connected or you risk damage to the output transformer.

DIY-Amp-Line-Out-Box.jpg
 




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