Odd's n Ends Revisited 6V6 SE amp

[Sparky OR]

Anyone built the amp in 9/05 Audio Express by Graham Dicker. It is a 6V6 SE amp driven by a 12AX7 with potentiometers of 5k for the driver cathode and 1meg for the anode. I built it, because it seemed like a good way for a relative newbie to look at how these variables effect the sound. I used an old 5k SE OPT from a Curtis Mathis hi-fi. Sounds ok, and varying the cathode seemed to have lots more effect than varying the load. I used a cheapie Elenco function generator and an old Hewlett Packard scope to see the output results into an 8 ohm resistor. The amp did not have anything close to a square wave output an any freguency from 100 to 10khz. But when I added a feedback resistor of 6.8k bypassed by a 100pf cap I could get square wave out without too much "ringing?". Is square wave output indicative of anything relative? Or is it not worth chasing down?
Thanks

 

[DigitalJunkie]

Square wave response is worth chasing down,it's great for tuning the feedback network,among other things. 🙂

 

[Tubes4e4]

Also, square waves are very useful to test and optimize stability at complex loads. And they come in handy to determin bandwidth (upper and lower -3dB points) fast and easy.

Tom