tube synth diy

I'm building this one that you can find here:
http://www.cgs.synth.net/tube/noise.html
And i am thinking about adding pots, one on 2d21 pin6, and/or another
one on the 12ax7 pin2, did some one tryed this?is it a waste of time
and money? does anybody have some ideas excepted vactrol on pin7...
thank you