Hi, I recently acquired a Music Man 65 head from circa 1974. It outputs 65w RMS and has switchable impedance (8 or 4ohms). Also, it operates in Hi Power or Low Power (switchable). I haven't been able to find much information regarding the hi-low power settings, but I'm assuming the Low Power selection halves the output wattage.
So, I'm planning to run this thing at 8ohms into an 8ohm 2x12 cab running Celestion G12H-30w speakers. I know that if I run it in High power and max out the volume, I'll kill the speakers. However, I'm planning to run it at the Low power setting until I have the money to get another cab, which I plan to be another 8ohm 2x12 running Celestion Greenbacks (25w each). So, then I'll have two cabs with the amp set to 4ohms and assuming it delivers the power evenly among all the speakers, and my lowest rated speaker will be 25w, I should be able to safely handle 100w and only putting out 65w max from my amp.
Does anyone see a problem with this? I've always tried to match the wattage of my amps more closely to the wattage of my cabs than dudes at Guitar Center or other shops have advised me to, but never quite this close. I've been playing for 13 or so years, and in a touring band for 7. Half the musicians I know have told me it's a terrible idea, and the other half think it's a solid idea.
Any suggestions?
I'm also waiting to hear back from the people at Avatar regarding this question.
I'm a pain in the ass.
Thanks in advance.
~Adam
It ought to work like you said, if you put the 8 ohm cabs in parallel and use the 4 ohm output.
"A cheerful heart is good medicine."
Sounds reasonable to me. Don't know why people would think it's a bad idea.
"Work hard, rock hard, eat hard, sleep hard,
grow big, wear glasses if you need 'em."
-- The Webb Wilder Credo --
Any suggestions? ~Adam
Yes!!! DEFINITELY drive your speakers as hard as they will take WITH the head on top of the cabinet. As the notes vibrate the cabinet...they'll also vibrate the tube filaments in the head. (Use Telefunken's...they'll last longer.) I call this "chassis feedback" and it's a sound that's harder and harder to come up with in the Solid State Age.
Hope this 'elps!
Cat
"Feel what you play...play what you feel!"
At 8 ohms the amp will only produce about 70% power compared to operating at 4 ohms. So it will put out about 45 watts on the 65 watt setting (High Setting), about 21 watts at the 30 watts setting (Low Setting). You want to use the 8 ohm setting for your current 2 X 12, and when you add another cab you should use the 4 ohm setting.
So right now at 8 ohms, each speaker in your cab will get about 22.5 watts on the High setting, about 10.5 watts each on the Low setting. So these speakers can pretty much handle the power. I wouldn't totally max the amp out. At 4 ohms with two cabs, each speaker will get about 16 watts on the High setting, about 7.5 watts on the Low setting. So yes, this is much safer for the speakers.
By the way, there was info on this amp at Harmony Central.
http://reviews.harmony-central.com/reviews/Guitar+Amp/product/Music+Man/65+Head/10/1
The early models were all tube, later models had a solid state preamp and tube power section.
If you know something better than Rock and Roll, I'd like to hear it - Jerry Lee Lewis
That info about power changing with the impedance is true for solid state amps. With pentode or beam power tubes in the output stage, the power output changes a bit, but not much. (For triode tubes, it works the same way as with transistors.) What mostly changes are the relative percentages of various harmonics. The reason the output power changes little is that the screen grid is the main accelerator of electrons to the plate, and its voltage doesn't change as the plate voltage fluctuates with the current through the load. Also the reason for the extraordinarily high plate impedance of these tubes. The standard vacuum tube handbooks don't contain the graphs of power and distortion vs. load impedance, but you can find the more complete tube type data online for the common power tubes.
"A cheerful heart is good medicine."
