The new TA-20 looks interesting, anyone have more details on the architecture/design or sound?
I've had the TA-3 for several months now and can say for higher impedance cans it is fantastic. However, it definitely needed a 12AU7 replacement to sound it's best. I put a Japanese Baldwin (mullard design) tube and it's amazing with HD800. The warmth and more up front presentation is a great compliment to balance out the cool and wide balance of the cans, I'm blown away for the price.
Did try to change the 6P19 tubes, those are interesting. After buying about 10 on eBay, I could only find about 3 that were not micro phonic. However, the two Russian brands available sounded pretty much the same, and the stock Chinese tubes were pretty quiet anyway. The tube is a outstanding choice for an OTL amp, with a plate resistance Rp of about 100 ohms it's perfect for 300 to 600 ohm cans. I measured the output into 300 ohms and it managed 20V peak to peak, so that's some 2W into the HD800, which is double the allowed maximum. I'm listening to most stuff at 9 to 11 o clock on the volume knob. By 12 is starting to get uncomfortable and at 2o clock it takes your breath away (not listening volumes). Needless to say it drives them effortlessly!