i am designing/building a transformer coupled preamp. It uses a 76 tube loaded with a 4.5:1 Lundahl transformer of 210H. B+ is 225V, standing current is 4.5mA and cathode resistor is 2k7. Simulating in spice nets me a bias point of 12.5V. But i notice an oddity - as i raise the value of the cathode bypass capacitor my LF start rolling off. Not a lot admittedly; a 220uF nets me -.219dB @20Hz, increasing the cap to 470uF gets me -.299dB and a 100uF -.336dB. What gives? Surely a larger cap should result in greater LF extension?
