One bias pot for each tube

[Red Phoenix]

I want to do the bias mod for my 5150 but i'm thinking of having a bias pot for every single powertube and not only one for the whole set. Then there would be no need for matched tubesets anymore. But i'm not sure if then the circuit could become unbalanced in a bad way? Are there even amps out which have adjustable bias for every powertube?
Or is it just overkill and i should better do only the normal one pot mod?

If it's not overkill..Does anybody know (especially the amp-techs here) how i could realize that for the 5150? Instead of replacing the 15k resistor (R68) with a resistor and pot in the bias section i have to replace each 2.2k resistor (R202, R204, R206, R208) at the control grid (grid no.1, pin 5) of the powertubes with a suitable combination of resistor and pot? Or does it need a completely re-design of the powerampsection? As far as i know the voltage of the controlgrid controls the biascurrent..

But anyway i want a testpoint for every tube to detect single tube failures. I would do it this way.
"The way the bias test points work is pin 8 (cathode, right?) of each power tube is wired to a red terminal on the inside of the bias test points. Each red terminal has a 1-ohm 1% resistor that goes to the black terminal, which is then wired to ground at one of the power transformer mounting bolts." I'm not sure about the mounting bolt as ground, i guess the groundpotential of the chassis is used here and the cable was connected with a solder lug under the mounting bolt?
This biasprobe seems to work differently, or not?

Any suggestions? Wolfeman? TheWinterSow? And everyone else who have the knowledge ...

 

[7string]

You could do dual bias. You would have to add a second bias circuit and have 1 pot for each pair of tubes, usually the 2 inner or 2 outer tubes.

But, you probably don't have the room on that printed board to do this. Matched sets aren't that much more are they? It isn't a big deal when they aren't matched (to a point). Just buy a couple singles to swap in if you get in trouble.

Here is another probe that allows you to measure the current instead of the pin 8 cathode / 1 ohm voltage drop way.

http://www.el34world.com/charts/BiasChecker3.htm

 

[Shinozoku]

Randall RM100 has a bias pot for each power tube. Works like a charm.

 

[Red Phoenix]

Thanks for the infos
The biaschecker link is a pretty good and detailed how to! I will think about how that double bias could be soldered in. But when its not that simple i will first try the normal bias mod to hear if i prefer the sound of higher bias or not.

I will have a look at the Randall schematics (if i find them) just for learning how that biascircuit was designed compared to other amps. thanks!