Mark III --> 4 ohm cab?

[mesa verde]

I have a 2x12 cab (two 8 ohm speakers wired in parallel for 4 ohm load)
Yes - I already know I can wire both in series for 16 ohms but I also
use this cab with another amp head that can handle 4 ohm but not 16 ohms.
And so I want to use this cab with the Mark III head.
First - is it safe to plug the 4 ohm cab into the 8 ohm out or would
it be better to plug the cab into one of the 4 ohm outs ?
I know it is a safe 'mismatch' (if I must rewire in series) to run
the 16 ohm cab into the 8 ohm out. But I really need to know
if running a single 4 ohm cab is possible without creating any problems.
Thanks for any help or advice.

 

[trem]

Your Mark III should have a 4 ohm output jack. Just plug the cab into that jack, which is perfect ie. no mismatch. If you plug into the 8 ohm output you will have an unsafe mismatch.

 

[MrMarkIII]

If you want to be super-safe, put two jacks on the back of your cab, and connect one 8 ohm speaker to each jack. Then connect those to each of the 4 ohm jacks on the Mk III.

Running a four ohm load into the eight ohm jack is a safe mismatch.

Running a four ohm load into a four ohm jack is still the same safe mismatch, because each Mark III four ohm speaker jack is designed to handle an eight ohm load each, NOT four ohms each.
I quote from the manual:
"One 8-ohm and two 4-ohm jacks are provided. The Boogie is not very sensitive to speaker mismatches and will not be damaged by
them except that very low ohmage loads will cause the power tubes to wear out faster. A single twelve-inch 8-ohm, speaker should
generally be connected to the 8-ohm output on the amp. When using two 8-ohm speakers, connect them both to the 4-ohm outputs
provided (because the total load is 4 ohms in that case)."

Those dual four ohm jacks perform the same task as the single jack (?) on the back of your four ohm cab: parallel connection of two eight ohm speakers.

The bottom line is the Mark III is designed to handle one 8 ohm load in the 8 ohm speaker jack, or two 8 ohm loads, one each in the 4 ohm jacks, paralleled at the amp.

Download the Lonestar manual. there's an entire section at the end about hooking up various cabs of varying loads.

 

[trem]

If you want to be super-safe, put two jacks on the back of your cab, and connect one 8 ohm speaker to each jack. Then connect those to each of the 4 ohm jacks on the Mk III.

Overkill, although it is safe. It's the same as running a single 4 ohm load into one of the 4 ohm jacks. See explanation below.

Running a four ohm load into the eight ohm jack is a safe mismatch.

Nope, commonly that's called that's an unsafe mismatch. Do NOT run it that way.

Running a four ohm load into a four ohm jack is still the same safe mismatch, because each Mark III four ohm speaker jack is designed to handle an eight ohm load each, NOT four ohms each.

It's a perfect match. The 4 ohm jacks are taken from the 4 ohm tap of the OT. Look at the schematics. The two 4 ohm output jacks are hard wired in parallel. Two 8 ohm loads (cabs) in parallel is 4 ohm; that's why two 8 ohm cabs should be connected to the 4 ohm jacks. If only one of the two 4 ohm jacks is used then a load of 4 ohms should be connected to it.

Just to make this clear, the most common scenarios are:
1. Connect one 4 ohm cab into either one of the two 4 ohm jacks.
2. Connect two 8 ohm cabs to the 4 ohm jacks, because the two being in parallel the total load is 4 ohm.
3. Connect one 8 ohm cab to the 8 ohm jack.

 

[mesa verde]

Just to make this clear, the most common scenarios are:
1. Connect one 4 ohm cab into either one of the two 4 ohm jacks.
2. Connect two 8 ohm cabs to the 4 ohm jacks, because the two being in parallel the total load is 4 ohm.
3. Connect one 8 ohm cab to the 8 ohm jack.

Thanks for that info. Much appreciated.