In our Ultra and Fet Valve products, the vacuum tube is operating in an ideal environment, not loaded down by having to drive any significant load. This improves the linearity of the tube by typically 10 dB over more conventional designs. In addition, each half of each tube has its own independent isolated high speed, high voltage analog regulated power supply. Power supply interaction is nil, and the supply impedance is very very low. Our designs let them behave at their best. This tends to minimize tube sound differences. We don't care if the tube gets in trouble when loaded down (a major reason for many tubes sounding "different") because in these designs, they are never loaded down.
There will still be sonic differences between tube brands, but less than expected in other products. My own listening tells me that old new stock Telefunken tubes are really nice, but very expensive and not possible to use in production. The JJs are about as close as we can come at real world prices, and electronic design research here is done with the JJs in circuit as we don't want to optimize for unobtainable tube brands.
Frank Van Alstine
