Ok so is it really this simple????

[MonsterBass101]

My friend wants me to make him a box that will allow him to route one input into two amps.  Essentially a Y-splitter.  Is it really as simple as taking a the tip from the input and route it to two different outputs?  thanks.

[Ripthorn]

If you aren't worried about one amp loading the other, then yes.  If you want them isolated, you have to use transformers (typically).  Most passive a/b/y boxes are just a couple switches and three jacks.

[Mark Hammer]

Well in one sense, yes it IS that easy.  However, it is also likely that your friend will shake his head and say that something is just "missing" in the tone.

Far better to throw something like this together: http://www.muzique.com/lab/splitter.htm

That will easily fit into a 1590B box with a pair of DPDT stompswitches, two LEDs, and three jacks.  Jack explains on the web page how to wire up a switch to mute the output of each part of the splitter.  A DPDT switch is all you need to mute/unmute a single channel/amp and show whether it's on with an LED.  If you space the two switches just so, you can even step on both either independently or at once.  That'll get you A/B/Y/none with plenty of isolation between the two amps.

Not to say that you won't find a use for what you initially proposed, but myspidey senses tell me that you'll get more mileage, and more satisfying mileage out of the active unit suggested here.  As the web page notes, there are no special requirements for the JFETs.

[petemoore]

  That's a nice signal splitter.
  Lifting the input ground requires an expensive transformer.
  I used it with a couple 15w amps and didn't notice increased hum when I connected the ground loop.