I'm not a tech and do not know exactly where in the power circuit the voltage drop takes place. All I can verify is that the Splawn site says "lower plate voltage to give the QR more sag & feel", and the plate voltage readings from my amp. Sorry, that's not much help, lol.
I asked only because I emailed Scott a week or so ago and asked about the plate Voltage in the QR. he told me it runs around 490.....that's why I was concerned about what power tubes would/or wouldn't be good for the amp. Just about every spec sheet I've seen on just about every tube says that an EL34 can handle 800vdc. So technically any tube I've looked at would work. I got concerned when Doug from Doug's tubes told me he didn't trust the New Sensor products above 450vdc. I didn't ask him why....
Not to long ago I tried some new tubes in my quick rod. My tubes went out so I installed some Siemens for the power section and Tung sol 12ax7 in the pre. Wow super Marshall sounding and very crunchy. But I think what did it for me was the all Tung Sol power/pre. The amp sounds like a Marshall, but with more low end. The Tung Sol really changed the sound, took out a lot of the very round min/lowend and tamed the over all sound. I love these tubes so much.
I can totally see how some one might not like them, but man so sparkly and evened out. My new choice of tubes.