From a different thread.......by Todd (BlueOliveB3)
Many RV Leslies had their reverb systems removed when the reverb amp Leslie came up with failed, as a large number of them seem to do, I've run into a few and never have I seen one that worked. I've never sat down and troubleshooted one (maybe I'll grab the one sitting at the shop and fiddle with it) but I suspect the two-transistor(!) input stage is at fault...they should have just used a low-noise 12AX7 for reverb recovery at that time like the Hammond reverb amp used. The twin sets of louvers were for 251 and 251RV applications, for other models they'd block off one of the sets. It kept the number of different cabs spec'ed from Cal-Craft (Leslie's cabinet supplier during the Pasadena era) to a minumum to save production costs, since the same cabinet could house a 122RV, 147RV, 251, or 251RV. When a technician removed a faulty reverb system another block-off would typically be installed. In the 147RV that dspiffy and I have we just removed the 6X9 and put the box back in place. I prefer a dry Leslie and just use the reverb in my A-100...the 12" reverb speaker makes for a lush tone.