How would one add an external speaker jack to a Fender mini amp?

[mickeymickey]

I have a Fender Mini Twin that I'd like to use as a head. It has a headphones jack but no external speaker jack, so I'd like to add one to it.

Now, to do this would I take the leads going to the mini amp's speaker and solder them to a separate jack? It seems like that would work but I have little experience with this type of mod, so I figured I'd ask here.

Also, would it be possible to use the headphones jack as an external speaker jack? I'm unsure of the impedance of headphones, so I'm not sure if that would work out.

[Threefish]

I don't know much about headphone outputs, but I wouldn't consider using it. It will have a lower output, and I'm guessing you want more.
As you said, take the wires from the existing speaker terminals, and solder them to (I assume you meant) a socket. Make sure you get them the right way round - for a normal 1/2 inch jack and socket wire to speaker +ve (could also be a red or other colour dot) goes to socket tip connection, wire to speaker -ve goes to socket sleeve (earth) connection. From here you connect it to a speaker or cabinet suitable. If your exisiting speaker is 8ohm, use an 8ohm speaker or cabinet. Those little mini amps are solid state aren't they? Be careful - you could also retain the connections to your existing speaker, and run wires to another speaker/cabinet, but you need to be very careful. If you parallel too many speakers (of too low impedance), the impedance your amp sees will go down too far and you could lose it in a puff of smoke. Could be worth contacting Fender to see what they (don't) recommend. Sounds like you don't have a users manual. I can't imagine it would cover converting a mini amp to a fire breathing monster anyway, though I think you can do it with those little smoky and pignose amps. It would be interesting to hear how this works out mickeymickey.

[birt]

use a switching jack.

the - of the built in speaker stays connected to ground, the + goes to the switch. then connect the tip of the switch to the signal coming from the pcb and the ring to ground.

if there is no jack inserted the built in speaker will work. if you plug in cab the built in speaker wil be switched out and you'll hear the cab instead.