Metropoulos Forum

I remember reading a Bias Formula depending on the plate voltages.

Can anyone help me with this?



Thanks


Lou

The formula for your target bias current is based on idling the amp at 70% of the maiximum heat that the tube plates can dissipate. Most EL34's, 6L6/5881's are rated for 25 watts of heat dissipation (nothing to do with the amount of power the tube can put out.)

70%(25watts)=E*I where E is your plate voltage, I will be the target maximum bias.
In the case of the 380-390 plate volts you (I think it was you?) posted in the Marshall forum,
70%(25watts)=380*I
17.5=380*I
17.5/380=I so your max bias current would be .046 amps, or 46mA.

Dude Thank you soo much. That makes total sense...I will make adjustments to the amp as it is set at 35...

The fact that it is running lower , does that mean cleaner or diry tone out of output tubes...



Thanks again