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Mesa Boogie Caliber 50+ Question
Old 10th September 2011
  #1
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AllAboutTone's Avatar
 

Mesa Boogie Caliber 50+ Question

Ohm issue.
The head offers (2) 4 ohms or (1) 8 ohm jack, I have a 16 ohm 70s marshall cab vintage 30s.

Can I use the 8 ohm jack with no worries?
Not sure how Mesa builds there amps in that way.


wow I put this in the wrong place, I meant instruments, guitars. amps......Mods please move. Sorry
Old 10th September 2011
  #2
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You can definitely use a higher impedance cab. It is a cab of lower impedance to the amp that is a problem. In fact, I sometimes find that I prefer the tone with a 16 ohm output than an 8 ohm output.

Think of the amp as a voltage source. The higher the impedance the lower the current. The lower the impedance, the higher the current, and on it goes to the point of destroying the power source.

Hope that is helpful.
Old 11th September 2011
  #3
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Thanks, just wanting to be safe.
Old 11th September 2011
  #4
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My pleasure.

Actually the Calibre .22 is one of my favourite amps. Is the Calibre 50 much different?
Old 11th September 2011
  #5
Only in power rating. The early non plus models used 4 el84's and the plus used 6l6's.
Old 11th September 2011
  #6
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Did exactly that (8ohms out) for a few years, nothing blew up. I'm gonna pick one of those heads up again some day, the one with the 6L6's. I used to use a reissue Junior with a P-90 and that head into a Marshall cab, sounded great.
Old 11th September 2011
  #7
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I love this combo unit. I owned for 5-6 years. Killer metal tones. REALLY loud for a small box. Wow.
Old 11th September 2011
  #8
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You're getting some good info and some bad info here, let me try and summarize:

Using a guitar amp with a non-matching cabinet impedance causes changes in function that differ depending if the mismatch is higher or lower. And most modern amps will tolerate a 2:1 mismatch in either direction, although it's not guaranteed to be safe.

Cab is lower impedance than the amp is looking for: tubes run hot, as if they were biased hotter, they sound more saturated and distorted. They wear out sooner, but as long as the amp is well built a tube wearing out won't break anything. Pretty safe!

Cab is higher impedance than the amp is looking for: at low level mismatches (less than 2:1) the power tubes run cool and last longer. However, they have insufficient internal resistance to counter the "flyback" voltage thru the output transformer from the speaker returning to the rest position. If the mismatch is too great this can cause arcing in the tube sockets or even in the output transformer which can destroy it. NOT safe!

Remember, tube amps are the opposite of SS amps: you CAN'T use an impedance that's more than 2X the listed impedance without risking catastrophic damage! This is why Fender Blackface amps have a shorting jack, so that if you forget to plug in a speaker cab, the circuit is a closed short meaning 0 impedance, which is safe, vs infinite impedance which can and does kill a Marshall or Mesa amp (forgetting the speaker cab and turning the amp up louder because you can't hear anything, not that I've ever done that).
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