cool, ill let you know if it works out.
why will this work differently than the volume controls on the guitar or preamp?

less chip points but more information, thanks.

phatt, this is an interesting solution. ill look into it. what kind of volume control? a limiter? compressor? volume pedal?

joe, the problem happens on multiple cabs.

well im hoping you half-assed electricians aren't chalking this one up as a win.

what the hell are "chip points?"

no it doesnt have a 4/8ohm switch.

the amp doesnt have an overheating problem. its also the case that most of the reviews on that link are positive. i studied it prior to buying.

this problem occurs hot or cold. i can use the amp for hours as long as its plugged into the 16ohm input. i really think teemuk is onto something with the muting circuit. i cant seem to find anything out about that though.

oh, the name of the amp is in the subject line. its a randall rh200. the front looks like this
http://img1.classistatic.com/cps/kj/090625/686r1/919736j_20.jpeg

i cant find a back pic, ill have to get to the studio and take one.

the back has a lift ground and an effects loop. the 4 ohm output is 220w and the 8 is 200w.
ive heard about an overheating problem with these amps, ive never experience it just this cutout problem.

cab is
http://www.amazon.com/gp/product/B0002GLE9S
(its only a very breif run down)

and i cant find a head description.

yes its a solid state. yes it sounds like what teemuk is describing, like a relay is switching something off. why does the amp thing its outputting to a hazardous load?

im using a 200 watt randall head with a 300 randall watt cab. when i output the amp at 8ohms and connect to the cabs 16 ohm input, i have a wonderful, sufficient, metal amp. when i output the amp at 4 ohms and input it into the cabs 4 ohm input the amp is about twice as loud but cuts out when i play low chugging palm muting. its not a speaker pop, the speakers can take it, the cab stops making sound. if i run the 4ohm output into the 16ohm input its identical to the 8ohm output in sound and volume.
when i was first looking for a cab, i thought my head was broken. it does this on other cabs too. its too bad because it is a loud amp but it seems to be hiding its other testicle in the 4 ohm output.
thanks to anyone who will educate me. i dont have the cab specifics but i can find them.