All good questions.
The name Surface started as an adjective, as in an audio amplifier for a Surface tablet computer. Then, as time went on, the adjective became a noun.
[font=Roboto, Noto, sans-serif]https://youtu.be/hdsvCpaWFWQ[/font]
I choose build a preamp to drive the input of Surface, because inside Surface not enough gain to be driven from just the headphone jack from a laptop computer. I was going to use Surface as the preamp, and have it drive a power amp stage. But, at the last minute, I choose to have Surface driven from an external preamp. I choose to build it as a 6V6 gain stage, as a rebuttal for S***** throwing me off from DYI*****.com. He did it first , I'm going to do it better....... Although Surface does not include electronic power braking ( I only use that to generate over-drive tones ), it does include my take on what a morph control could be.....
LED biasing. I've always used lamp biasing in all my gain stages , audio amps and guitar amps.. .... and no you don't bypass the led bias lamp with a cap... let's just say it's personal preference.
Why a 6v6 tube, instead of varies 12ax(x) tubes ? I read once , it was the opinion saying "big" tubes generate "big" tone.
I once did a big SE guitar amp using one 12ax7 / T / 12ax7 / 12au7 / EL-34 for the treble tone control channel , and one 12SL7 / B / 12SL7 / 12SN7 / KT-88 for the bass tone control channel , and then mix the both of those into the primary of the O/T ; for a client from Sidney. One could see how I divide the tone stack in half, and then recombine them at the O/T.
Ya , big sound from that one, for sure.........
-g