psyche:
I am trying to control some solenoids and the pwm frequency has to be 19.5Hz!!!
That seems a very odd requirement. Are you quite sure it has to be exactly 19.5Hz, rather than at least 19.5Hz? Can you provide a link to the solenoid datasheet?
Although timer/counters 0 and 2 are limited to approximately 30Hz and above on a standard 16MHz Arduino, you should be able to get a single 19.5Hz PWM signal from TC1. Set the prescaler to 64, register OCR1A to 6409, and OCR1B to 0-6409 to get the required on/off ratio. That will give you a frequency of 16000000/(64*(6409+1)*2) = 19.5008Hz.