Odd Reverb Q (Silvertone content)

[Antero]

My amp is a Silvertone 1484 head, which I absolutely love - it sounds amazingly ballsy.  One peculiarity of the design, of course, is that the reverb is notoriously useless as reverb.  The reverb feeds back on itself, creating a crazy volume boost and strange sustain.  I, of course, think that that's pretty awesome (especially with volume swells). 

My question is, what the hell is it in the reverb circuit that causes that, and would it be conceivably possible to create something similar, say, in a box with a volume control after it so it doesn't eat everyone else I'm playing with?

Thanks!

((silvertone 1484 schematic: http://www.freeinfosociety.com/electronics/schematics/audio/silvertone1484.pdf ))