A quick biasing question (or two)

[ricks57custom]

I just finished replacing my pre-phase master with a post-phase master and this thing is really rocking now. A have two quick and dumb questions about my bias:

1) I checked the current and the amp is running @375 VDC at plate 3. According to the conversion info I read, the bias on the EL34s should then be 46ma @ 70% dissapation. Is this correct?

2) Right now my bias is at 38.5ma and that's as high as it will go. I can't remember: Do I increase or decrease the size of the resistor at the end of the bias circuit to get it in range (I'm using a bias tap and bias config off the PT)?

Thanks for the help in advance. My amp has become a real crunch beast. I LOVE IT!

[Mark]

Dear Rick

I assume that you are using the bias circuit from the A4 circuit. I also assume that you want to increase the current flowing through the output tubes.

It is pretty much as you've alluded to. You have a 10K pot with one side of the pot being attached to a 15K resistor to earth. The closer the control grid gets to earth he more current the valve will draw. Reducing the 15K resistor is the ticket. I wouldn't remove a resistor value from the circuit as it might become difficult to adjust the bias due to the pot making too great a change in the bias voltage, and the second thing is the 10K pot on it's own may load down the bias supply.

I hope this helps, feel free to ask questions.