>- it does not have positive dc offset so i wanted to build a new one.
All you have to do is add a 39 k ohm resistor from the 9 V rail to the output end of the 1 k output resistor (according to Dr. Clark) so that when the output goes low it will be at approx. 1/4 volt.
>- which frequency have you found most useful for tapeworms, parasites etc thnaks.
It is my general feeling that people will get better results from using both 30 kHz and 2.5 kHz than just one frequency. The 2.5 kHz does appear to penetrate the internal organs better though.