I've got a freakin chart and everytime I need something that aint on the chart I forget. I just need the dissapation calculation math. Thanx

Thanx OTM but let me make sure I've got this right. percentage times dissapation divided by plate volts equals cathode current? Youve got all this technicaly looking right I'm sure but I'm gonna need the Red Neck version.

Here's a very useful site, great when you forget everything. http://www.kimber.com/atomic-struct/BC5-10.htm E (voltage)= I (current) * R (resistance) and all the other variations which can be figured out by manipulating the equation.

Keith, looks like you're calculating exactly per the formula Tele gave, so that lines up. Also, after adjusting the current, you want to double check the plate voltage because it can vary after the bias resistance has been changed. And finally, you may not want to peg it at 70%, but you may want to choose a lower number if it sounds better to your ears. 70% is the maximum suggested per the tube specs.