Mark Five head and 4X12 cab switchable 16 ohm or 4 ohm

[bandit2013]

The golden rule no matter what the amps make is. Never use a cabinet of lesser impedance than the rated output as this will overload the OT and may potentially damage it.

The only exception would be for Bass amps that can handle a 2 ohm load. Always read the manual so you do not wind up with an expensive repair down the road. I run a total load of 2 ohms on my TT800 but it can support that (also has a switch for that connection).

Worse thing one could do, and I can see it happen is one may plug in two 8 ohm cabs into the two 8 ohm jacks. The same could hold true if both cabs would have a 4 ohm switch and they were both plugged into the 4 ohm jacks. Understand the basics of what parallel means.

Total load (parallel) = (cab1 x cab2) / (cab1 + cab2). this is the standard equation. They easy thing to work out if the cabs are the same, just divide the single cab impedance by 2. or do the math which will have the same result. If the cabs are different, do the full math if you want any sense of accuracy.

 

[DECEMBER]

Again, my experience is different. You keep mentioning what you've read, not what you've experienced. What I've read by most manufacturers is any mismatched combination is not recommended. What I've experienced is most modern tube amps are designed to handle that stress.

Some additional info: Click here, and here.

Not saying the output transformer and/or tubes aren't stressed. Lower impedance results in a higher current draw, higher impedance results in higher flyback voltages. Both situations are capable of causing component failure. Ultimately, it's your decision whether or not the risk is worth it.

Well, yeah, I've never "experienced" the results of mismatching because I can't afford to gamble my $2000 amp. And it's not that difficult to get the right speakers and match impedance properly. So I'll continue following the advice of every tube amp manufacturer and keep my impedances matched.
It's like deciding to use a condom... you'll probably be fine, or a year later you could find out that you're gonna lose everything.
Why risk it? I've never been in a situation where all i have is a 4 ohm cab and an amp with only 8 or 16 ohm taps and I just have to plug it in and crank it right now. There's always a solution... if it's a 4 ohm 2x12 or 4x12, it can be rewired in series to 16 ohms. There's just no good reason to risk a mismatch.

 

[rarebitusa]

FWIW food for thought... this link below is a good technical guide on really what happens with tube amp mismatching. Any mismatch means that the power generated gets lost as heat somewhere. Heat of course can be damaging to components when their rated limits are exceeded. WRT Mesa output transformers they are certainly designed to withstand the "one step" mismatch. What they also show in their documentation often is the use of an impedance matching box.

Impedance Matching Tube Amps

What I find interesting is what Weber calls out here "It is dangerous to run a HIGHER impedance cabinet or speaker" vs which Mesa says is safe. but it's all about the increased flyback voltages and how much is really too much.

Weber Z-Matcher

Either way the details are there. In the end it's really about "safe" vs optimal with the added caveat of how hard are you driving the amp output. Especially if you have that Spinal Tap Marshall amp that goes to 11.

 

[rarebitusa]

Some additional info: Click here, and here.

Sorry I just noticed see you already outlined the link, my apologies for not catching that.

 

[Elliot Twist]

I would probably just run the cab switched to 4 ohm and use the 4 ohm tap on the amp. At least that is a proper impedance match.

Review the manual if you are uncertain. It can be found online from Mesa as well. At least it will be up to date if any changes were made.
Customer service pages also detail how to connect cabinets of different impedances, much the same as in the Mark V manual (the one I have downloaded some time ago) covers that on pages 53 thru 58, much of what others have referenced or stated.

Yes, you're right. I was using the 16 OHM cab on the 8 OHM output for a while.
I think I'll just switch the cab to 4 OHMs and use the 4 OHM output.
I was just looking for opinions.

 

[Elliot Twist]

The golden rule no matter what the amps make is. Never use a cabinet of lesser impedance than the rated output as this will overload the OT and may potentially damage it.

The only exception would be for Bass amps that can handle a 2 ohm load. Always read the manual so you do not wind up with an expensive repair down the road. I run a total load of 2 ohms on my TT800 but it can support that (also has a switch for that connection).

Worse thing one could do, and I can see it happen is one may plug in two 8 ohm cabs into the two 8 ohm jacks. The same could hold true if both cabs would have a 4 ohm switch and they were both plugged into the 4 ohm jacks. Understand the basics of what parallel means.

Total load (parallel) = (cab1 x cab2) / (cab1 + cab2). this is the standard equation. They easy thing to work out if the cabs are the same, just divide the single cab impedance by 2. or do the math which will have the same result. If the cabs are different, do the full math if you want any sense of accuracy.

Yes, you're right. I was using the 16 OHM cab on the 8 OHM output for a while.
I think I'll just switch the cab to 4 OHMs and use the 4 OHM output.
I was just looking for opinions.

 

[Elliot Twist]

Well, yeah, I've never "experienced" the results of mismatching because I can't afford to gamble my $2000 amp. And it's not that difficult to get the right speakers and match impedance properly. So I'll continue following the advice of every tube amp manufacturer and keep my impedances matched.
It's like deciding to use a condom... you'll probably be fine, or a year later you could find out that you're gonna lose everything.
Why risk it? I've never been in a situation where all i have is a 4 ohm cab and an amp with only 8 or 16 ohm taps and I just have to plug it in and crank it right now. There's always a solution... if it's a 4 ohm 2x12 or 4x12, it can be rewired in series to 16 ohms. There's just no good reason to risk a mismatch.

Yes, you're right. I was using the 16 OHM cab on the 8 OHM output for a while.
I think I'll just switch the cab to 4 OHMs and use the 4 OHM output.
I was just looking for opinions.

 

[Doug Doppler]

FWIW food for thought... this link below is a good technical guide on really what happens with tube amp mismatching. Any mismatch means that the power generated gets lost as heat somewhere. Heat of course can be damaging to components when their rated limits are exceeded. WRT Mesa output transformers they are certainly designed to withstand the "one step" mismatch. What they also show in their documentation often is the use of an impedance matching box.

Impedance Matching Tube Amps

What I find interesting is what Weber calls out here "It is dangerous to run a HIGHER impedance cabinet or speaker" vs which Mesa says is safe. but it's all about the increased flyback voltages and how much is really too much.

Weber Z-Matcher

Either way the details are there. In the end it's really about "safe" vs optimal with the added caveat of how hard are you driving the amp output. Especially if you have that Spinal Tap Marshall amp that goes to 11.

Hey @rarebitusa - YES, matched or higher when it comes to tube amps > cabs. Short version, my amp guy works on my amps, and a few guys whose first names are Joe, Neal, Kirk, and James. I've got a High Power Twin here on loan (formerly owned by Keith Richards), and while I will only run it at it's 'correct' 4 ohm load, my amp guy verified that higher (4>8, 8>16) will not damage anything. Lower is where get into trouble. Been busy, always nice to 'bump into you'. Back soonish with more amp nerdism