High Current / Low Current / No Current ??????

Ohm's law (V=I*R and W=V*I) is in operation here. Say a typical transistor amp is capable of delivering 25 volts into an 8 ohm load. That'd give 3.125 amps of current, which is about 80 watts.

Hook the same amp to a 4 ohm speaker and the current demand is now double at 6.25 amps needed. However, if the amp can't supply the extra oomph, they you have a current limited amp. If the amp can deliver the extra current, you now have a 160 watt amp into 4 ohms instead of an 80 watt amp.

Magnepan 1.2 and 1.6 speakers are 4 ohm units so will demand more current from a transistor amp than an 8 ohm speaker. Some transistor amps will be challenged by this and not respond well.

Most tube amps run their output tubes through a transformer that changes the output voltage to match the impedence of the speaker. The max current stays constant whether 4 or 8 ohms (assuming the output transformer has both taps) but the max voltage changes. An 80 watt tube amp will deliver the same watts & current to both a 4 ohm or 8 ohm speaker, but the 4 ohm speaker will get double the voltage.

The max current stays constant whether 4 or 8 ohms (assuming the output transformer has both taps) but the max voltage changes. An 80 watt tube amp will deliver the same watts & current to both a 4 ohm or 8 ohm speaker, but the 4 ohm speaker will get double the voltage.

Not exactly, max power stays the same but both voltage and current change.

The 4 ohm doesn't get double the voltage of the 8 ohm, that would produce 8 times the power.

The 4 ohm gets .707 of the voltage that an 8 ohm speaker gets and draws 1.414 times more current. This keeps the power the same for both.

Herman, thanks for the correction. Shows the perils of replying off the top of one's head.

Sheesh. If an amp is making 100 watts into 4 ohms it is the exact same amount of current whether the amp is tube or transistor. Ohm's law (and the Power formula which derives from it) says so: 100W = Current squared times Resistance.

The speaker is 4 ohms so:

100W=5 squared x 4 ohms. IOW the current is 5 amps at 100 watts.

The idea that its a good thing that the amp power doubles as the load is cut in half is a bit of mythology. What this suggests is that you won't always have flat frequency response in your room with every amplifier (notwithstanding the effects of the room itself).

A further note: in the past I've seen amps that claim that they can make 80 amps or some such. What exactly are they try to say? Giving the benefit of the doubt, let's use a one ohm load for the amp. This gives 1600 watts! 'Current' ratings like this are actually a rating of how much current is available when you short the power supply for 10ms. We do that easily with our tube amps...

The fact of the matter is that in general Magnaplanars sound better with tube amps then they do with transistors. They don't always play as loud, but they do sound better. 'High current' amplifiers (IOW: transistors) are about volume rather then finesse.

Try the the moscode 600 and forget about the theories. there is one for sale on this cite.