jcm 900 mkIII combo safer connection with mesa boogie 4x12 cabs

[otokorou]

Hi guys! I would like to tell me your opinion about an issue i have...I want to connect my jcm 900 mkiii 50 watt combo (two outputs for external speakers, one switch to choose either 4 or 8 ohm) with two mesa boogie rectifier 4x12 cabs (each one is 4 ohm stereo / 8 ohm mono). My first thought was to connect the two cabs from their 8 ohm input socket to my combo's outputs, choosing 8ohm's resistance (having the switch of my combo at 8ohm selection). Of course i want to use all of the speakers from the cabs, not only a pair from each one. So is it safe to make the connection with the way i describe above?

[g1]

Set the amp switch to the 4 ohm position, connect to the mono input of both cabs.
Two 8 ohm cabs connected to the amp makes a 4 ohm load, so that is what you set the amp switch to.

[pdf64]

Just to expand, the speaker jack sockets on the back of the amp are in parallel, so two 4 ohm loads (cabs configured in stereo?) connected in parallel would be 2 ohms; as that's too low for any of the amp settings, it may stress the power tubes.
It may be possible to buy or build a simple adaptor to put the two x 4 ohm cabs in series, creating an 8 ohm total load, which could be matched to the amp.

[g1]

The cabs are 8 ohm each in mono, he wants to run both cabs so that will be 4 ohm load.

[otokorou]

The cabs are 8 ohm each in mono, he wants to run both cabs so that will be 4 ohm load.

[otokorou]

That's exactly what i mean. I want to run 2 mesa cabs (each of has 4 ohm stereo and 8 ohm mono option) through my jcm 900 combo (look the figure above, i know it's not so representative :-)). I am not sure whether the two ext speaker output sockets of my amp are 4ohms or 2ohms each one when the switch (ohm selector) is set to 4ohms..

[g1]

The 2 jacks are in parallel.
So when you have the switch in 4ohm position, you can run one 4 ohm cab, or two 8ohm cabs.

[otokorou]

Thanks a lot dudies!!

[52 Bill]

Thanks a lot dudies!!

For all of the above to be true, the internal combo speaker must also be unplugged from the amp.

[g1]

Thanks 52Bill, I totally missed the big bold COMBO in the post title.
However, he did mention using both speaker out jacks, so I assume he was planning on disconnecting the internal speakers.

[TimmyP1955]

For a soundman, the only thing worse than a guitarist with a 4x12 is a guitarist with two 4x12 :-)

[Justin Thomas]

I prefer 50W&2x15" + 50W&4x10" myself... >:O

Justin