#1
So, I have a Fender Machete 50W head.
The head has an OHM setting switch of 4, 8 or 16.
My question is:
Which OHM setting will run the head at it's potential?
Will it work harder (or hotter) at 4 OHM vs 8 or 16 OHM?
Will it work less (or cooler) at 16 OHM vs 8 or 4 OHM?

I know enough to match the speaker ohms to the setting on the amp and have the luxury of having my choice of cabs.

I want the amp to last.
Will using one of the 3 choices help prolong the life of this amp?

Thanks!
#2
The best bet, is to match the ohms. With it matched, you will get longevity. If you want to "expirement" always set the amp lower than the cab. For example, if your cab has 2x12 speakers, each at 16ohm, wired together is effectively 8ohm. Now you can set your amp to either 4 or 8 ohm, I suppose setting it to 4 ohm would drive them a bit harder. Setting the amp to 16ohm will kill the amp though DONT DO IT.

Having a choice of cabs is nice. I'd say to keep it simple, use whichever sounds best and match the ohms.
#3
If the amp and cab ohms are matched, it doesn't matter.
“Ignorance more frequently begets confidence than does knowledge.”
Charles Darwin
#4
Since your amp has an output transformer, it doesn't matter.

Well to use a bit less winding on the output transformer you may wanna use the highest impedance possible so to gain a tiny bit of efficiency, but that's nothing audible, it's just to make you feel better with yourself.

Match the output impedance from the amp and the input impedance from the cab tho, whatever they are.
Name's Luca.

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#5
It will work "harder" (actually just less efficiently, but practically the same thing) with an impedance mismatch, e.g. 8 ohm head into 16 ohm cab or 4 ohm cab. If you care, you lose about 11% power output with a 2:1 or 1:2 mismatch. Mismatches beyond 2 in either direction are not usually a good idea with a tube amp.

With an impedance match, there is little if any difference between any of the ohm settings. Conventional wisdom is that given the option you might as well use the 16 ohm tap because it uses all the OT windings but that's probably more of a feel-good "any answer is preferable to no answer" than something that actually matters.

So to answer the question, there's probably no difference at all but if you have all options available to you there's no argument against 16 ohms. None of them will "run the amp at its potential" appreciably more than the others.
#6
Quote by Roc8995
Conventional wisdom is that given the option you might as well use the 16 ohm tap because it uses all the OT windings
Being the OT a stepdown transformer shouldn't be the lowest output impedance setting to use all of the windings?
Name's Luca.

Quote by OliOsbourne
I don't know anything about this topic, but I just clicked on this thread because of your username :O
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Clue: amplifiers amplify so don't turn it on if you need quiet.
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#7
Nope.

Remember that when you are stepping down impedance, the "least stepped down" tap is 16 ohms. The most stepped down is 4. A "zero transformer" (one whose output was the same as input) would have identical winds on both sides, so it makes sense that more windings on the output side gets closer and closer to the input impedance which is in the range of thousands of ohms.

You step down by removing turns on the output side. The input is, let's say 8K ohms. So you'd remove some number of turns to get down to 16. Now to get to 4 from 16, you still have to remove some turns, right? (You could imagine using a second output transformer here if you like) So you make the 4 ohm tap remove some turns to get it farther away from the input impedance. So the highest impedance tap uses more turns on the secondary.

Does that make sense?
#8
+1 Colin

I have a cool diagram somewhere if I can find it.

Quote by Koldgrin

I know enough to match the speaker ohms to the setting on the amp and have the luxury of having my choice of cabs.

I may have been the only person that picked up on this statement

Quote by Koldgrin

I want the amp to last.

There are other things you can do to prolong the life of your amp though, namely starting with the tubes.
#9
Quote by Roc8995
Does that make sense?
Yes that does, thank you for the explanation
Name's Luca.

Quote by OliOsbourne
I don't know anything about this topic, but I just clicked on this thread because of your username :O
Quote by Cajundaddy
Clue: amplifiers amplify so don't turn it on if you need quiet.
Quote by chrismendiola
I guess spambots are now capable of reading minds.