Hi I have a 4x12 cab, and a Fender Frontman 212R. The Fender Frontman has a Power in so I can use it as a cab. And a pre out so I can use it as a head. Well I'd like to use it as a head for my 4x12 cab, but nothing is sending the cab power because it's not an external speaker jack on my FM212R but only a pre out. Is there anything I can buy, that'll power the cab, and so that I can connect them and make a half stack? Thanks, any help would be great.
That's not how power in/pre out work. A head is a combination of a power amp and a preamp. A cab is just a box with a speaker. What you're looking at is an effects loop - you can use it to use the amp as a preamp or a power amp, not a head or a cab.

Anyway, to do what you want, you need to get the power amp output (not the preamp output like you're looking at) to the cab. The power amp output is made up of the wires going to the speaker. You can wire those up to a 1/4" jack. Then you just have to plug a speaker cable from there to the 4x12. To use the internal speaker you'll have to wire the speaker wire to another jack and use a cable between them, or wire those bare wires coming off the speaker to a speaker cable to plug into the jack you made. You're basically adding an external speaker jack and then using the internal speaker as if it were an independent cab.
I'm confused on how I'd go about doing this. I get lost at wiring the power amp output to a 1/4" jack. How would I do that?
And what exactly does just a preamp do and just a power amp do? Basically, what's the point of having them on the amp?
There are two tabs on a 1/4" mono jack. Cut the speaker wires in half and solder one wire to each tab, on each side (polarity doesn't matter). Now you have an external speaker jack. Stick a speaker cable into the jack connected to the amp, and plug it into the 4x12 or the other jack you wired to the speaker.

A preamp shapes the tone, a power amp makes it loud. You really need both to have an amp.
I'm lost on the soldering part. I'm confused on what exactly I'm soldering, like I get the wires from the speakers from the amp, but what do I solder that too? And I'm also confused on once I do that how I have an external speaker jack. Is there a cable I need to get, that takes in a 1/4" cable?
I don't mean to be rude, but if you can't figure that out, you shouldn't be doing it. This is as simple as it gets.

You have two wires from the amp to the speakers.
Cut them both in half. Solder a jack onto each pair, so you have a pair of jacks where once there was a continuous set of wires. To make them continuous again, put a speaker cable connecting those two jacks.
To use a different speaker, unplug the cable from the speaker jack and plug that same cable into another cab.
don't bother doing it. your amp wasn't really designed to be used as a head, otherwise it would have had a speaker out. you will have to do semi-permanent modifications (which you don't seem to have the understanding to do), which I wouldn't think is worth it.

to answer some other questions:
Crudely speaking, the pre-amp adjusts the signal from the guitar. the EQ, gain and any other tonal controls are located on the pre-amp. the power amp takes the signal from the pre-amp and makes it louder, thats it. the pre-amp out allows you to put effects after the pre-amp (as opposed to putting them infront of it by simply plugging effects in between the guitar and the amp) but before the power amp (effects cannot go after the power amp)
I'll outline this with pictures.. It's very very simple and about as basic as it comes to soldering. In a nutshell, soldering is gluing together electrical stuff with a glue that conducts electricity. Keep in mind you can only run the 4x12 cab or the speakers in your cab separately. They both can't be running at the same time. You have to make sure the Ohms of the cab match the load the amp was designed for.

See the white and black wires coming from the amp? Not the ones between the speakers, but the ones between the amp itself and the speakers? You would take those 2 wires and disconnect them from the first speaker (which disconnects both speakers) and then solder those 2 wires to a 1/4" mono jack.

(Invalid img)

That's what the jack looks like. See the two little tabs on the sides with the holes? That's where you would solder each wire respectively. It doesn't matter which wire goes to what tab, as long as it's one wire per tab. Ignore the long metal thing.


Once you done that it would be as simple as plugging the speaker cabinet into that jack you soldered using a speaker cable. Don't use a regular guitar cable. They look the same but they're not .

If you wanted to use the speakers inside the amp you would have to cut an end off a speaker cable and solder both wires inside said cable to the little tabs on the speaker inside the amp. I'm referring to the tabs you pulled the white and black wires off of in the beginning of this. Then you would simply plug the speaker cable from those speakers into the jack you soldered.
Endorsed by Dean Guitars 07-10
2003 Gibson Flying V w/ Moon Inlay
2006 Fender All-American Partscaster
SVK ELP-C500 Custom

1964 Fender Vibro Champ
1989 Peavey VTM60

[thread="1166208"]Gibsons Historic Designs[/thread]