You asked about the Cayin A-50T. I've had one for a few months and am very impressed, great build quality and great sound. I think it's better than any of the three tube amps I'd had before, a Cary/AES AE-25 Super Amp with an AE-3 preamp, a Cronus Magnum and a Cary Sli-80 F1. It's especially impressive considering its price but I still think it sounds better with my gear than any of those amps, even the Sli-80, which cost multiples of the A-50T
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You're limited to El-34 or KT77 power tubes but even the stock Cayin El-34s sound good and the RFT/Siemens tubes I have are even better. I'll probably get some Gold Lion KT77s to try because I was very impressed with them in the Sli-80 and should have kept them when I sold the amp.