If it's a single channel, then it's a later one. The early models had two channels.
The early models could put 150 watts into a 4 ohm load. The power amp is a grounded bridge design which enabled sufficient output voltage across a 4 ohm load. These were not designed for 2 ohm loads and will eventually self destruct if presented with one.
The later models. Well, they were apparently designed for the marketing department. The marketing does rate them at 200 watts into a 2 ohm load. They might actually do it - for a short period of time. But if you expect them to do it for an extended period of time and at a high volume level (like max), it will eventually fail.
Unfortunately, to do this, the power amp design needed to be changed. The grounded bridge was out, replaced with two paralleled transistors per "side" to handle the increased current capability that was needed - to produce 200 watts into a 2 ohm load.
Both models use 2N3055 output transistors - 4 in total. The fifth one is the driver.
2N3055s are great for sound in my book, but only at lower wattage levels - like 4 of them for 100 watts is pretty safe. Even the 4 for 150 watts isn't bad because of the grounded bridge design of the earlier power amp.
However, using only 4 to produce 200 watts into a 2 ohm impedance load usually means that most of the time they will be operating in a secondary breakdown area... and they will break down eventually, much faster than the 100 watts into 4 ohm configuration will.
The later model will put 100 watts into a 4 ohm load, pretty much the same as the earlier model. If you do have a late model and plan to run it pretty much full out, go with a 4 ohm load. The 3db difference between 100 and 200 watts will barely be noticed.
However, if you really want 200 watts, the only way to do it is with a 2 ohm load. If you go this route, at least swap out the output transistors to something a little better rated. Even 2N3773 types would be better than 2N3055 in this case (and you don't need "vintage" ones that are selling for ridiculous prices - look on Mouser).
Try this for comparison and understanding - look at something like a mid-70s Peavey Musician 400. These are rated to do 210 watts into a 2 ohm load. They have EIGHT 2N3773 output devices, not just four 2N3055 devices like the Concert.
