Interesting..as for the tubes. I was talking with a new old friend, who was in the tv/electronics repair business for years.
He had some interesting things to say on tubes. He mentioned the good tubes will hold their "specs" under load and not drift much. He also mentioned, concerning this size tube. Particular tubes of the same number where designed for specific purposes. Some low frequency oscillation (like the Tesla), other for a more wideband use. He gave me a couple 70's (I think) reflector corp military tubes to try.
I did notice that the Tesla had a fuller low frequency response then the GE upgrade tube. Not mushy, just fuller.
Apparently the getter part has really little to do with the performance.
I haven't really heard a comparison of the Burson vs Sparko in a D1/D2. I wonder is some of the difference simply has to do with what piece of equipment its going into.
I have to say, the D1 is really a amazing/fun and great sounding piece of equipment.
It, along with my NOS Dac's have really changed how I listen to music it. Made it fun again!!
As a side note, the Maverick D1 with the Tesla has much of that NOS sound.
I think anyone that is really tired, or growing tired of their digital sources should seriously look at the Maverick, or NOS options.
In most cases they are pretty good bargains. Considering the value, and sound quality you get for your investment. Not to mention the fun!!