You can expound on what MDG5 said and also apply it to calculating the cathode bypass cap (or freq, or resistor), but then you should take into consideration the Ra (anode resistance of the given tube...12ax7, etc.) and the anode resistor...and the mu of the tube, too (i.e. 100 for 12ax7). Ra will vary with ...
Upper case letters tend to designate components external to the tube while lower case letters tend to designate internal characteristics.