Adjusting Frequency on an LED Flasher

[eev_carl]

Hi,

I've implemented this LED flasher circuit but I can't visually discern the flashing.  I verified with a scope that there is oscillation, but the frequency is 47.8 Hz rather than the 12.5 Hz listed in the description of the circuit.  I have different PNP and MOSFET transistors: 3906 and 2n7000 respectively.

Am I able to tweak the frequency with simple R or C substitutions or do I need to expand the circuit?

Thanks,
Carl