How to spot a high current amps?

Thanks to everyone for the quick responses. The points of listening to all equipment and never trusting a manufacturer's figures are well taken. Unfortunately, short of buying each individual piece and then reselling it on audiogon, I will probably never be able to hear most of the amps I would be interested in purchasing.

While I think that what I am wondering about is an A/C, not a DC circuit, could I apply P=I(squared)R to figure out how much currrent an amp will push, given a known speaker resistance and output power? Perhaps this is a gross oversimplification that will lead me down the wrong path.

For the most part, a (conventional) amplifier's maximum current delivery is dependant on the power rating (of the transformer(s) used, rated in VA or KVA. The higher power transformer rating, the greater current delivery potential (all else being equal).
In non-technical terms, the more difficult it is to physically lift the amplifier, the higher its output current delivery will be!

peter jasz

Hmm. I have amps with current rating, eg., 45 amps, 40 amps, 60 amps. One of them is not difficult at all to lift. Very light in fact, an old Mission Cyrus One integrated that feels like it weighs a pound or two. Yet it was rated at 40 amps, but only 25 wpc. Now, I'm sure you think that's just marketing talk, but the fact is that I used to drive a pair of KLH 5's with it(about 77db efficiency) and it's never had trouble with any pair of speakers. It is a little light on the very bottom, a little warm in the upper bass and seriously rolled off in the treble, but still a very musicallly dynamic little amp.

In general, however, the heavier amps do seem to be rated for higher current.

Paulwp, welcome to the world of marketing by specs.

Remember, power = current squared times resistance. Using 40 amps and 25 watts, this says that:

25 = (40)^2 * r where r = resistance. solving for r we get a value of about .015 ohms.

In other words, if those numbers are correct, the amp only delivers 40 amps into essentially a dead short. What is the minimum impedance the amp is rated to drive?

At 8 ohms the amp could deliver about 1.8 amps, and at 4 ohms about 2.5 amps. This assumes the amp delivers 25 watts at both impedances, which is probably not true.

In short, these numbers don't really make sense.

I also like the weight test mentioned in previous posts.

As always, trust your ears.

I remember reading an ad by a mfg. (Adcom?) who said to remove the top of the prospective amp and look at its main fuses. If the fuse is rated to blow at 20 amps (or whatever) how can the amp put out more? -Valid question...