First let me apologize to Alun and others for any confusion my post of the formula to calculate the freqency. As it turns out the formula is incorrect. When I did the calculation I got a negative number. I knew that could not be right so I ignored the - sign. I did some checking and find that the calculation is a little more complex, but the attachment shows a general formula that is extremly close when the Vcc is 9V. Audioguru is correct about the reverse-biased transistor. In the case of the 2N3904 my current data books did not list the maximum negative bias for the subject transistor, so I actually measured the avalanche and found it to be very close to 7.5 volts. Actually measuring the - bias of the circuit my scope showed 5.2 volts.