BUILDING NOTES 1) in the original schematic of the VCO frmo thomas henry we three times a resistor R26, whereas R25 is missing completely. so here are the values corresponding to the PCB labeling that are not covered correctly by the schematic/parts list: R25 - 300k R26 - 39k R55 - 5.6k 2) when powering from 12V:
R13 = 2k
R27 = 22k
R33 = 137k
3) when you have a hard time finding a precision trimmer wit 25k, just use 50k. does the job as well. 4) C4 is the timing cap. use a nice C0G/NP0 or a mica for better stability.