1. Should I pick Single End (SE) or Push-Pull (PP).
2. Is Class A PP any better than Class AB or Class B?
3. Should I use Ultra-Linear or Triode mode
4. Negative Feedback — it is OK?
5. Is chinese amp any good?
1. SE or even Singe End Triode (SET) or PP? Less is more. SE (or SET) has less electronic components on the signal path, so SET has less influence on signal, has less sound deterioration. At the extreme, only one resistor, one tube and one transformator will do.
Push-Pull has 2 tubes, working in opposite directions, doubling the output power. More bass, more volume, less detail and imaging.
So, is it quality or quantity what count for You?
2. Ok, it gets more complex. Push-Pull can work in class A (both tubes in constant action all 360 degrees), in B (only 1 tube in full action in 180 degrees, only when it’s phase) or mixed — AB. In short, its pretty much the same. A gives less power, but cas cleaner sound, AB is a compromise between distortion and power. Class B is so distorted, that is not generally used in audio systems.
3. Get decent high-efficient speakers and Triode mode. Triode versus Ultra-Linear is again fighting for additional power. You lose power, going to Triode way, but gaining quality. Use high-efficient speakers and You will not lose in listening sound levels.
4. As little Negative feedback (NFB) as possible. NFB is to cure other issues in circuitry. Good SET does not need any NFB and sounds brighter than one with NFB. Negative Feedback is for gaining good characteristics on the paper, not for human ears.
5. Give a try. Your ears will tell. I got one and like it! If You don’t like it, sell it. Anyway, they are 5-10 times cheaper than audiophile European or USA made units.
Every technique to improve efficiency and power in tube amps, causes added distortion. My advice is to purchase high efficient back loaded horn type speakers. I recommend full-range 1-speaker crossover network -less setups. These speakers allow to use simple single end triodes with very few components on signal path. Crossover-less full-range speakers are easy loads for amp and final result will be precise imaging and uniquely airy feeling at regular listening volumes.