Voltage drop resistor calculator for bias.

[joesatch]

I  have a layout that is taking a 100vac bias tap through a 120k resistor for a bias circuit. (after the 120k resistor goes to the reversed diode as normal). I'm assuming the amperage on the 100v is less than 500ma.  What voltage is the result after this dropper?  I ask because i need to change the value of this resistor because my PT is delivering a 50v ac for bias.

[sluckey]

It's common to see a 470Ω to 1KΩ resistor used with a 50VAC bias tap. But it all depends on how much negative voltage you need to have on the grids of the output tubes. Showing us your schematic would be very helpful.

[joesatch]

the bias voltage from the PT is 100v as per a diagram i'm looking at. My PT bias tap is 50v. What do i change that 120k resistor to?

[Willabe]

I think Sluckey wants to see the whole amps schematic.

He want's to see the power amp tubes and dcv's they'll be run at.

Different power tubes at run different dcv's need different -bias dcv to tame the tubes output. Less dcv on the power tube plates, you run them with more current, so less -dcv. Higher dcv on the power tubes plates, you run them at less current, so a little more -dcv.

[SILVERGUN]

the bias voltage from the PT is 100v as per a diagram i'm looking at. My PT bias tap is 50v.

What does this mean, exactly?

[Willabe]

I think he means he's looking at a schematic showing a -bias circuit that he want's to use, but the schematic he's looking at, the PT has a 100vac bias tap.

And the PT he has and wants to use only has 50vac bias tap.

So he see's double the vac from the tap on the schematic and wants to know how change the value of the bias dropping R to go with the 50acv tap that his PT has.

Is this right Joe?   

[joesatch]

I think he means he's looking at a schematic showing a -bias circuit that he want's to use, but the schematic he's looking at, the PT has a 100vac bias tap.

And the PT he has and wants to use only has 50vac bias tap.

So he see's double the vac from the tap on the schematic and wants to know how change the value of the bias dropping R to go with the 50acv tap that his PT has.

Is this right Joe?

Jackpot! 

[sluckey]

Use a 470Ω 1W resistor. Look at this schematic...

    http://sluckeyamps.com/misc/bandmaster.pdf

[joesatch]

Use a 470Ω 1W resistor. Look at this schematic...

    http://sluckeyamps.com/misc/bandmaster.pdf

Beautiful layout