I have a randall rg100 combo amp that i dont use anymore, i still do like it but it just cant play at high enough volumes. Im pretty sure the combos have the same amp head as the sold seperately heads so if i hooked it up to a matching cab do you think it would sound just as good as a real head?
It should sound as good, but you just said your problem is it cannot produce a high enough sound pressure level. A cab won't change your SPL....you could buy a cab and buy an amp, like one used for a PA system. Run your headphone out to that amp, then connect the cab to the amp. Presto, you should have the same tone as your head usually does, just louder. Of course, the speakers used might change the tone somewhat.
Of course its not going to sound exactly the same but it will be close. I dont know about that amp but on mine when you plug in cab it bypasses the speakers of the combo and just drives the cab.
100 watts is enough power but the problem is once it gets to the high volume coming out of two speakers the sound gets muddy so it really needs 4 speakers to distribute properly