Brian, I know we have had this discussion before, but I offer this evidence from thewho.net:
Baba O'Reilly
Equipment used: Lowrey Berkshire Deluxe TBO-1 organ from 1968.
Lowery TBO-1
I’d always thought this was programmed into Pete’s huge modular ARP 2500 synth/sequencer. It certainly sounds like it could have been! It’s hard to believe that the sound we hear on Baba O’Riley is really a Lowrey home organ. The model Pete used was a TBO-1, but for anyone wishing to recreate Baba O’Riley, just pick one up the following models to do the same job: TLO, DSO, TLS, TSO 25 and HR and GAK (seems to be the nearest). Pete is using a setting called “marimba repeat.” This is different from a normal repeat effect in that certain notes are repeated either on or off the beat creating a much more complicated repeat pattern. For example the following group of notes sound ON the beat when these keys are held F-G, B-C#, and these other notes G#- A#, D-E repeat off the beat creating the alternating pattern heard on Baba O’Riley. In addition, a setting called Wow-Wow is used, much like a guitarist’s wah-wah pedal. It’s not that obvious in the Who’s Next version as it’s only being used as a tone control; but in Pete’s orginal demo, the effect is used in the regular way. It’s often been reported that Pete recorded the part at half speed, making playback sound fast and frantic (Terry Riley often did this), and again sounds possible but it is performed in realtime. If you get the chance to try one of these organs, hit that marimba repeat tab and you will quickly realise how it inspired Pete to come up with this fabulous keyboard part.