How to spot a high current amps?

Cdc and Gs bring up very valid points i.e. yet should teach us one thing: everything is relative.

Having said that, i think that it is generally accepted that an amp that "doubles down" i.e. produces twice as much power as impedance is cut in half is considered to be "high current" for its' power rating. I would go so far as to say that some amps are "high current" even though they might not "quite" make it to doubling. As Gs stated, obviously an amp that is rated for 300 / 600 is going to produce more total current than an amp rated for 50 / 100, but the ratios of voltage to current amongst the two would probably be quite similar. The biggest advantage to using the larger amp would be that you would have a much greater level of dynamic headroom which in turn would allow one to play louder with less fear of pushing the amp too hard / clipping.

Bare in mind that the above is refering to SS amps as tube amps are a completely different beast when it comes to power output vs impedance. Most tube amps are making use of output transformers and are relatively current limited when compared to a "decent" SS design. In terms of OTL ( Output Transformer-Less ) designs, it would not be out of the ordinary to see an amp that put out less power as the impedance was reduced. This has to do with the output impedance of the tubes / circuitry itself since there is no output transformer acting as an impedance matching device to help the tubes along.

Other than that, there is a LOT more to "good sound" than having high current capabilities. Linearity in terms of THD / IMD, bandwidth, frequency response, transient response, level of bias, etc... are all other specs to take into consideration too. The bottom line though is how the unit sounds to you in your system. I've seen / heard plenty of combo's of "good" gear that simply did not match well together. I'm sure most others here can attest to similar experiences also. Sean
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I think this is simple: there is no answer. I would not even go so far as to believe the power-doubling-into-half-load being a good sign because there is no standard in how the power is measured. There are all kinds of tricks - don't understimate the power of marketing. Just try the amp you think should work and see for yourself its performance. This way, the results are 100% accurate! Arthur

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.