So my goal this summer is to try and to build a tube based VCO, and so all I have right now are just plain vacuum tubes, not thyratrons like Metasonix and other people are using right now. But a problem I am hitting is that the normal equations used in predicting the frequency f=1/ln2 *2(r1c2+r2c1) commonly used for transistors do not apply, but the equations mentioned here http://www.radarpages.co.uk/theory/ap33 ... h6p112.htm that forget the ln2 term seem to work, but it seems only a limited range of grid resistors given a set plate resistor and capacitance.
I notice the plate and grid resistances seem to combine, but the equation only mentions one resistor value for each tube independent of plate resistance, are there more accurate equations I can use?
So essentially I'm trying to see how I can get a wide range of predictable behavior out of a vacuum tube multivibrator. The tube I am using right now is a 6SN7. My goal is to eventually build my own tube based VCO which will be utilized in a synthesizer, not necessarily using a 6SN7.