If you want to build a Twin T to this spec:
Schematic below. Use 2C=0.0022uf (code 222) and C=0.001uf (code 102). Resistors are 6.8kHz. Wire two together in series to make one R of 13.6kHz (you'll need to do this for each R), and use one alone for R/2. Or find something very close to 13.6kHz for the R resistors.