Bias Calculators.

EdGrip

Today I have noticed that all of the other bias calculators on the internet suggest bias settings about 4mA higher than the Weber bias calculator for 70% dissipation. I am confused. Who should I believe?

ICBM

Depends on whether you prefer the sound with it hotter or not, and whether you're concerned about valve life.

There is no right answer, the 70% is only a guideline. Hotter is not always better for tone either.

It also depends on whether you include the screen current in the calculation, which you do unless you specifically subtract it if you're measuring via a bias probe in the cathode path. Since Weber's settings are presumably based on using the bias probe they sell, they may be including the screen current, although 4mA is only a guess at that too since it varies.

EdGrip

So the 4mA difference is accounted for by the calculator allowing (or not) for the screen current? 

Cheers as always.

ICBM

EdGrip said:

So the 4mA difference is accounted for by the calculator allowing (or not) for the screen current? 

Probably. I don't know, I haven't seen the figures. I tend to allow 5mA if I'm measuring via the cathode - but it's not exact, and it doesn't really matter. If you use the unadjusted figure you will always be on the safe side anyway.

ESchap

EdGrip said:

So the 4mA difference is accounted for by the calculator allowing (or not) for the screen current? 

Cheers as always.

yes, it's in the Weber blurb somewhere