I understand the principal of negative feedback, but since there is a capacitor between the stages, wouldn't that cause a phase shift in the signal, and when feed back into the input tube, would not that phase shift, from the source signal, cause some distortion?
Correct, every time you feedback a signal you get a 45deg phase shift. As a designer I occasionally try a feedback circuit in my tube designs, but I'm far from an expert and have never liked the results. All of my designs are Pure Class A, that's the sound I've fallen in love with. In pure class A you have a phase intact signal from beginning to end, with no feedback.
Very curious about your experiments with the 830-B!! I'd love to someday build a SET amp that puts more than 10wpc (like the 300B amp I'm currently running).
Yes a high power tube amp would be fun. If a tube is rated for 60w, typically you can only expect about 15wrms in Class A, that's how inefficient SE amps are! I've owned large amps and small amps and in my opinion the best combination is efficient open baffle (dipole) speakers and SE single ended monoblocks. And here's the amazing thing my little 2w Yuri monoblocks sound better than all the other higher powered amps I've owned. Some of it has to do with the linearity of the tubes and circuit, some with the quality components and build, but I think at the foundation is a straightforward design with minimal circuitry, short runs and attention to small details like how the heater circuit is designed and fed overhead to the tube pins. This is one quiet amp!
I wasn’t watching but listening in my car and I was waiting to hear what value resistor you used. You talked about experimenting then you didn’t say what it was (I think). I know it depends on taste and the circuit but I was curious.
This Tube Lab was filmed a long time ago, but if I remember correctly I experimented with 3 levels of FB, using a low, med & high resistor value and a couple of return points. Don't ask me what the resistors values were, maybe if you watch the video I showed a working schematic. The key take away for me is in class A tube circuits I really don't like the results of feedback. For me as an audiophile and designer, clarity and musicality are my prime goals (after I meet the basics - low noise/distortion etc). And imo feedback messes with the phase and clarity of the signal.
