Mesa 4x12 OS - ohm reading

Luca79

Active member
My friend bough this old Mesa cab, probably have 20 years. It look in good shape and sound good, but when i was cleaning and opening it, i measured the resistance. I read something like 30-32 ohm, with the cable plugged in the 8 ohm port. Is this normal? I checked the soldering joints, and all the speakers seem to work fine.
My cabs don't have the 4+4 and 8 ports, so is a different wiring... first time to see a so big difference.
 

glpg80

Well-known member
Seems like someone goofed the wiring and put everything in series (four 8 ohms in series)

You can use a meter to get an idea of what the cabinet is wired for but it’s not for exact measurements since it’s measuring resistance at DC and not impedance for AC at some frequency.

I’d still check the wiring, the soldering doesn’t matter if it’s wired wrong.
 

tpruitt

Active member
I just bought an old mesa cabinet and had the volume cutting in and out. I had to clean the jacks. And the main jack is kind of a strange one too. Has a piece of plastic on the tip that I had to “adjust” back into place. I’ll keep an ear on it and will order a new one if needed.

So make sure to really clean that jack!!
 

Luca79

Active member
Tonight i will reach my friend, clean the jack and measure the resistance again. Anyway the cab was sounding fine, very similar to my Marshall with V30.
 

BeZo

Well-known member
My guitarist just blew his amp in a similar situation. We had to bend the tab on the jack back to get the switch to function properly. Gotta watch the jacks on Mesa cabs. That's why I rewire things to mono.

There was more to his problem than just his cab though. Luckily nee tubes fixed everything (after I bent the jack back).
 

Luca79

Active member
My guitarist just blew his amp in a similar situation. We had to bend the tab on the jack back to get the switch to function properly. Gotta watch the jacks on Mesa cabs. That's why I rewire things to mono.

There was more to his problem than just his cab though. Luckily nee tubes fixed everything (after I bent the jack back).

Strange. I think even if the resistance is higher, it should be safe for the amp.
 

Nigel

Well-known member
My guitarist just blew his amp in a similar situation. We had to bend the tab on the jack back to get the switch to function properly. Gotta watch the jacks on Mesa cabs. That's why I rewire things to mono.

There was more to his problem than just his cab though. Luckily nee tubes fixed everything (after I bent the jack back).

Yep. Done three Marshall 4x12's with the toy like switch plate of fail. The Mesa backplate came straight from the based department though, it is legit.
 

BeZo

Well-known member
Strange. I think even if the resistance is higher, it should be safe for the amp.
I started troubleshooting for him and found the cab issue. You are right. He uses a Mesa Fifty/Fifty and tried to run it mono. I keep telling him he can't, but he thought otherwise and blew half of his amp.

The manual says you can run it mono with the volume at zero and be safe. I trust Mesa's products more than I trust some of the things I've read in their handbooks. Lesson learned (I hope).
 

BeZo

Well-known member
Yep. Done three Marshall 4x12's with the toy like switch plate of fail. The Mesa backplate came straight from the based department though, it is legit.
I had a pile of those boards at one point. Friends don't let friends play Marshall cabs with the stock wiring.
 

Nigel

Well-known member
I had a pile of those boards at one point. Friends don't let friends play Marshall cabs with the stock wiring.
You are a scholar and gentleman, good sir. Here here!

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