Combining Guitar and Bass amps....

you're gona need an active crossover to split your signal before it goes to the amps... I know carvin makes one, but i'm not sure how great it is, i'm sure other companies make em too.
but the real reason i'm replying is that your porn/tabs signature thing is the coolest, i just had to say that

 

Various and sundry players have used Marshall, Orange, Hiwatt, Ampeg, Fender, and Music Man tube guitar heads paired with a bass cab. And some '70s heads — the Music Man HD 130 [non-reverb] and the Ampeg V-4/V-4B, for example — seem to be pretty interchangable in terms of use with guitar or bass. You probably won't find anything above 150 watts in this category, but paired w/ a 2x15, many of the brands mentioned above are crushingly loud anyway. And tube fuzzy.

 

relman, are you looking to use a guitar head and a bass cab or split your signal to go through a bass and and a guitar amp? Doesn't Chris Squire do this to add some high end grind to his sound? If splitting you signal is what you want to do you can get a line splitter and play full range through both amps or you can get a crossover and send the highs to the guitar amp and the lows to the bass amp.

I do agree with Mr. Grieves that you won't find anything over 150 watts.

 

You could also just run a line out of your bass amp into a guitar amp, then roll off the lows so you don't damage the speaker.

 

Go check out www.12stringbass.com and look under the Bass Notes section. They have a couple of articles talking about splitting a signal into different frequencies. Even though they are talking about 12 string bass stuff, it still is applicable.

I know that Tom Petterson of Cheap Trick does this signal splitting thing, although he splits it into 3 different amps. Also, Eddie Jackson, the bass player for Queensryche, has done this in the past. For Operation:Mindcrime, he had his normal bass rig, and then had a single 12" guitar speaker in a sealed enclosure to put some grit on the top end of his recorded signal.