Double PCL84 PushPull Audio Amplifier V1

Simple push-pull configuration of two PCL84 TriodePentodes. All resistors are 0,25W. PowerSupply is simplified by using simple 230V-12V transformers. Output transformer is an ordinary 230V-12V transformer as well. Isolation tranformer is a cheap miniature chinese 1:1 audio isolation transformer (red tape on winding and white tape on core), take note of its phase orientation. Gain is set by R13 feedback resistor value, R13 = 0R is unity gain, R13 = 220R is 2 and R13 = 1k is close to 4. Feedback Error amplifier is in a common cathode + common anode triode configuration with bootstrap and light positive feedback for maximum gain (Resistor R6 sets the positive feedback ammount, lower value equals higher gain but less stability). Frequency response is greatly limited by choice of the output transformer, toroidals work the best while EI transformers usually cutoff at around 2 kHz. Output power is rather low, around 4W in an ideal case.