OK... apparently they DO have 2 grade levels:
The US places seems to be selling the cheaper (non-Blackplate) version.
Yes there are 2 grade levels, the str version, which is cheaper, and the blackplates series.
The second picture is the tube I have, and I was talking about this tube in my previous post. Sorry if it was unclear, I am not a native english speaker
The tubes branded TAD, means tube amp doctor, a german company specialized in guitar amp parts.
TAD tubes are made in the shuguang factory in china. They are made using a special equipment and tooling, with a schematic specific to them.They are then pre-burned in and selected and matched in germany, hence the "premium selected" branding.
The blackplate series, are basically the same, but the anodes have a black special coating, which is supposed to help with linearity and heat dissipation.
I think they are great tubes, very reliable, and have a sound of their own, I mean those are not just plain rebranded shuguang tubes. ( could be the case for some small tubes , but i don t know for sure )
Further listening confirms my early impressions, a bit richer sounding than the gold lions, but I am not sure yet if that is because the highs are recessed or if they are neutral with more body.
I have only 2hours of listening on them so too early to make a statement.
Moreover I use my desktop computer as a source, and I have a usb pci filter card coming with a linear power supply, as I figured playing with the bifrost 2 usb and coax input from the reclocker produced vastly different results.
by the way
@ThanatosVI was the psaudio powerplant an improvement in noise floor for the ha-6a ?