How did the tube rolling end up here? I went with GE JAN-5670W (https://www.amazon.com/gp/product/B07T86S6HP/ref=ppx_yo_dt_b_asin_title_o09_s00?ie=UTF8&psc=1) and preffered them to the stock tubes. However, arguably a bigger positive difference came by upgrading the power supply. The stock power brick is a 12V-1.6A unit that is not enough for this amp. With the GE tubes and stock power, this amp would start to distort noticeably in the midrange on my 6XX once the volume got to about -35. The more I pushed the volume, the more it distorted and lost timbre in the midrange. I realize that some level of distortion is the point of tubes, but I’m talking about the mids going from sounding mildly tubey to losing tonality. On Amazon’s site someone had asked if it was safe to upgrade to a higher current power supply and the manufacturer said it was. So I grabbed a 12V-3.0A brick (https://www.amazon.com/gp/product/B07NR6FPN9/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1) and what a difference! The midrange on the 6XX is much more “stable” as the volume increased.
So, I highly recommend a tube roll to the GE tubes linked above and upgrading the power cord/brick from the stock. At current prices that makes the P20 more of a $135 amp, but it’s still a great way to get into balanced amplification and slight tubiness for the price. (Currently listenign to Led Zeppelin’s In Through The Outdoor album at ~70dB on my 6XX’s, the volume on the P20 says -20, it just sounds tubey, no excess distortion).