Making and tuning 6v6 push-push pull amp using the Chinese PCB and a bit modified original schematics.
The transformers are TBT ATR 12:
After the actual tweaking of the amp trying to deal with ringing and overshoots, according to this post about Amplifier Compensation (also read this), here is also a simulation with LTspice, which is easier to play with and which actually also shows the same problems with ringing depending on the values of C3 and R28 for the “lead” network and C4 R2 for the “lag” network. The required file is my6v6pushpull, the models for the 6SL7 and 6V6 tubes are from here: 6SL7 and 6V6
Data from the real amp and visualization with Python, the influence of the lead capacitor C3 on the actual closed loop gain when the feedback is set to be rather low (6dB).