tyco octavia question

[edad]

I put my ggg tyco octavia pedal together some time ago and it sounded fine,but I used a different value on r5,one day last month I got some 220k resistors which is what it called for,I installed it and to my ear it didnt sound right,but Ive lost the other resistor and am only guessing as to its value.I tried a 100k and the octave was almost gone and ossilated on full.
  what is the job of this resistor and could I put a pot there to fine tune the value and then install the correct resistor? would I use a 250 or 500k pot?   thankss