Limited B+ with a VVR - Which is the way to calculate the resistor ?

[kagliostro]

A simple VVR we use is this



The 47k resistor set the lower voltage that can be reached

if we want we can add one other resistor between B+ and the pot to drop the higher voltage that can be reached rotating the pot to the max



I don't know how to establish the value of the added resistor, so I've think to the sum of resistor + pot as a resistor voltage divider

I did a bit of math and to me seems that around 420K will be a good value for that resistor
(assuming 350V B+ and 250V the max voltage to have on the output)

Can I consider that as the right way to calculate that resistor ?

Thanks

Franco

[sluckey]

That's the right answer (actually 418,800Ω), so I assume you did it correctly.

[kagliostro]

Many Thanks Steve


Franco