Can I do this?

You would still end up with a 4 ohm load but one cab would be out of phase with the other, resulting in a hollower sound.

 

You could rig this up so the two cabs are in series, but you would need to either rewire the sockets in one cab so that the second socket is a series output, or make up a special 'daisy chain' cable with three plugs on it. The first option is probably easier, but you'll need a switched jack if you ever want to run that cabinet on its own.

 

You need a heavy-duty DPDT switch. Use the best, most reliable switch you can.

Here's how to wire it.

Series/Parallel switching

Strictly speaking you don't need both of the connections in the 'X' pattern at the bottom, but fitting both increases reliability by using both switch contacts in parallel - always a good idea especially for speaker connections.

This gives parallel when the switch contacts are in the 'up' position (with most toggle switches that's when the toggle is down) and series when the contacts are in the down position.

 

No trouble!

Make sure the two parts of the 'X' are not touching each other, BTW, if that's not clear from the drawing! I tend to use solid copper wire for them, and put a little bit of insulated sleeving on one.

Should be quite an easy mod - a standard heavy-duty DPDT should fit in a jack hole.

Reliability is very important BTW - if the switch makes an intermittent contact, the amp could end up with no load on it. That's why I like to use the 'X' wiring, it significantly reduces the chance of this happening.


Just as an aside, I use this wiring method for 'true' bypass switching in pedals too - the usual scheme is to connect both of the two lowest tags in that diagram to each other. This is bad, because then in bypass the signal has to pass through both switch contacts - a bad contact in either will break the signal path. With the 'X' wiring, it would take a failure in both at the same time to cause trouble.

 

If you happen not to want to modify the cabs themselves, hears a diagram of the daisy chain cable that John spoke of earlier.

 

Sorry, somewhere in the thread I lost track that you were talking about 8-ohm cabs - obviously with 16-ohm speakers. I think it was the series/parallel switch question... I somehow thought you were talking about 8-ohm speakers.

Yes, you are quite right. If you series-wire the cabs with the switch, they will be 32-ohm cabs. You will need to connect them in parallel to make a 16-ohm load. A normal speaker cable connected between the two cabs will achieve this, or alternatively just connect them both to the amp - assuming it has two speaker outputs.

The only way to get a series connection is to use the special daisy-chain cable (unless you were to rewire one of the cabs so the second socket was a series-out, but that's getting more complicated than you need).

Don't whatever you do run the amp with a 64-ohm load! That would be a serious risk to the OT, even if the amp was set to 16 ohms.