As we begin our adventure into SPICE we needed a circuit to play with. The designer send me one like this.
The quest is to build a long tailed amp. (differential amp? the have several names) Anyhoo, I put this one up for an example. The amp is distorted. The waveform are the grids from left to right.
She saw the distortion being produced by my poor selection of grid resistors.
Increasing these resistor values worked wonders. Adjusting the cathode resistors helped too. She measured .5 volt our with 100mv input after the changes.
So back to the drawing board and this is the final. I also fed the transistor thru a divider because the base feedback was degenerative. The attenuator on the final input helped reduce loading on the preamp.