Like swapping-around different preamp tubes in PEDALS!
The possibilities exist!......I found this guy named Rick "DeMarco Electronics" on Ebay who builds distorton/boost/octave-above pedals that operate with a tube inside of them....and yes, the tube does work, not just one with a light-bulb behind the tube....lol! Anyways, he builds "GLASSBENDERS" FX.....sells 'em on Ebay......I got a killer Univox Unidrive UD-50 clone circuit built into a GLASSBENDER pedal design----and it uses a 12AX7 tube with supplied ceramic pin-out adapter (or 6SL7/6SN7 without). Absolutely fun. I've yet to try the other preamp tubes yet because the 12AX7 sounds so good. I use this pedal and a Danelectro French Toast (octave and reg. fuzz) through the Watts Model 24 exclusively for that late-60's Yardbirds sound.