This unusual amp – the Ek-O-Sound, also designated by Rickenbacker as the model M-10 -- was produced in very limited quantities and modeled on the EchoSonic amplifier designed by Ray Butts. This amp has tons of power driven through a single Jensen blue frame P12N speaker. It is also the first (and only) Rickenbacker tube amp to have a built-in tape echo/delay transport, a mechanical contraption located at the bottom of the cabinet with a circulating tape loop. The variety of tones this 11-tube amp will produce is astounding. A very rare and sought after amplifier.