12au7 (ecc82) curves.

[wozt]

The graph only goes to 20v bias, do I just pencil in 22, 24 volt lines or does the tube have a maximum -20 point?
What I am trying to work out is, if I want to center bias this tube, do I go for -10v, or would I take the penciled in curve of 24v and shoot for a -12v bias?
I currently have it biased at -8v as a cathodyne PI. I presume this is HOT bias?

Or does the central bias point not relate to the center point of the bias range but something else?

[uneumann]

[ATTACH=CONFIG]33525[/ATTACH]

The graph only goes to 20v bias, do I just pencil in 22, 24 volt lines or does the tube have a maximum -20 point?
What I am trying to work out is, if I want to center bias this tube, do I go for -10v, or would I take the penciled in curve of 24v and shoot for a -12v bias?
I currently have it biased at -8v as a cathodyne PI. I presume this is HOT bias?

Or does the central bias point not relate to the center point of the bias range but something else?

So, to your first question: The max neg bias on the tube is far greater than what's shown on your curves. This curve set just doesn't show them. Search for some other 12au7 curves and you'll find better and more useful data.

As for "center bias" that's a relative term in the sense that several factors impact what "center" means. Draw your load line and work from there and/or listen to the output signal and tweak the bias to taste.

As for cathodyne PI bias... while there is not enough info to answer your question, in general hot/cold don't mean anything for that circuit. It's all about getting the right dc voltage levels to maximize headroom.

Here is a 12au7 curve set I use ...

[überfuzz]

Valve Wizard has a page with links: The Valve Wizard Find a link to the load line plotter. With it you can mess about with different set ups and see what load line you end up with.