Power tube biasing and sonic differences

[greiswig]

I find it interesting that in my D'Lite amp with 6L6's, running about 430V on the plates, the amp sounds best biased cold: between 32-35ma per tube.

If I shift tubes to a pair of 6550s or KT88s (including reducing the grid resistors), the plate voltage drops a few volts. I have a choice: I could go with a correspondingly "cool" bias of around 42ma, or crank it on up to 58ma, which should be about 70%.

The 6L6's are running at a plate voltage more toward the middle of their optimum, from what I understand, while the KT88s are actually pretty low in their plate voltage.

The 6550s or KT88s sound better biased a bit hotter than the "correspondingly cool" point...they seem to sound best at right around 50ma. Does this have to do with the relative plate voltage preferences of the tubes? What are other people's experiences here?

[Structo]

I have my Winged =C= 6L6GC's at 41ma.
My plate voltage is around 434v.
That is around 50% according to this bias chart.
http://members.shaw.ca/house-of-jim/Htm ... ables.html

Isn't the actual measurement we get off of the 1 ohm cathode resistors a bit higher than what the tube actually sees?
Because of the screen voltage and other things?

I need to experiment a bit with the bias on my amp.
Seems like I like the 41ma better than when I had it at 35ma.

By the way I have 3K3 on the grids and 470R on the screens.