Negative bias regulation supply
Moderators: pompeiisneaks, Colossal
Re: Negative bias regulation supply
Autobias is something quite old.
Looking at the components on the pcb behinh I see for each channel: a resistor to see the current, an opamp comparator, a mosfet to set the biasing voltage, probably a low-pass RC filter to be able to remove the ac component of the signal and read only the dc part only of the current flowing though the tube (both screen and plate, being read on the cathode resistor). Almost all work that way.
Looking at the components on the pcb behinh I see for each channel: a resistor to see the current, an opamp comparator, a mosfet to set the biasing voltage, probably a low-pass RC filter to be able to remove the ac component of the signal and read only the dc part only of the current flowing though the tube (both screen and plate, being read on the cathode resistor). Almost all work that way.
Re: Negative bias regulation supply
Whenever I see "better imaging" claimed in regard to audio equipment, I tighten the hold-down strap on my wallet. 
Auto bias is indeed old. It was old when I designed an auto bias system for the Workhorse amp line. I got it all working, and then took it out in favor of a much simpler system with just a red-green-blue LED indicator for bias on each tube.
The Goldilocks system (too hot, too cold, and just right) takes about ten seconds per tube, and can literally be done between sets, or even between songs. Letting the human handle this in a non-meter-reading way is simple and effective. Auto biasing systems can be done, and can sometimes be done well, but this still leaves the question of whether it's what the user wants and or needs.
Auto bias is indeed old. It was old when I designed an auto bias system for the Workhorse amp line. I got it all working, and then took it out in favor of a much simpler system with just a red-green-blue LED indicator for bias on each tube.
The Goldilocks system (too hot, too cold, and just right) takes about ten seconds per tube, and can literally be done between sets, or even between songs. Letting the human handle this in a non-meter-reading way is simple and effective. Auto biasing systems can be done, and can sometimes be done well, but this still leaves the question of whether it's what the user wants and or needs.
"It's not what we don't know that gets us in trouble. It's what we know for sure that just ain't so"
Mark Twain
Mark Twain
Re: Negative bias regulation supply
To RG's point, an auto-bias system is a complicated bit of circuitry (from a tube amp perspective) that adds several more potential points of failure.