Have you contacted Steve at VAS Audio regarding the biasing? I can't answer you question but what is strange is that there is no biasing procedure in the user manual. I would think that infered autobiasing. But I was also warned about the fact that one of the CAYIN amps required "cracking" the unit open to bias. Hard to believe that such a great amp would be so difficult to bias. I sure wouldn't want to do that on a regular basis. My opinion; - - for optimal performance, bias should be checked occasionally and re-adjusted if necessary. After 100 hours or so, this is important regardless of which power tubes you use. My preference is GENELEX "GOLD LION" KT88's. The amp will never sound better, but careful with the pre-amp tubes. I have an A-100T which I love. Biasing is super slick. Sound quality rivals virtually anything on the market except for perhaps AYON. I have one of those also. But the pre-amp tubes for the A-100T are custom configured for this amp specifically. I tried NOS tubes with terrible results. That's when I checked with Steve at VAS and found this out. I'm not a fan of 6550's. They are more rugged but tend to sound a bit brittle with certain types of music.
That's about all I can add regarding CAYIN. The A-50T is a stone bargain provided that you have reasonably efficient speakers. Only 18W in Triode mode. It also has a top biasing set up with the use of a meter. Easy to use. Great little amp. Very reasonable price.
That's about all I can add regarding CAYIN. The A-50T is a stone bargain provided that you have reasonably efficient speakers. Only 18W in Triode mode. It also has a top biasing set up with the use of a meter. Easy to use. Great little amp. Very reasonable price.