Resistor voltage ratings

[vetmed]

I have a resistor rated 350 volts and would like to use it as a plate resistor where the B+ is ~375 volts. This would yield a plate voltage of 130 volts for a drop of 245 volts. Am I OK or should I look for a resistor with a higher voltage rating? TIA

Robert Lees

[Grainger49]

When you start you will see more than 375V to ground.  But... the resistor will not have any current through it.  So it will not have any voltage across it.

The key is when the tube starts to conduct.  Does the resistor ever see in excess of 350V across it. 

And I doubt it.  Give it a try.  Worst case is you could waste a resistor.

[vetmed]

Thanks Grainger, that's what I thought but I wasn't 100 % sure BTW this design uses a 5AR4 rectifier so the B+ comes up slowly and will never see excessive voltage so no need to worry about that case.

Regards
   Robert Lees

[Paul Joppa]

We've had instances where resistors have failed near their rated voltage. Some sources say that they can get nonlinear above 70% of their rated voltage. The simplest thing is to use two resistors in series.

Remember, the plate resistor will see nearly all the B+ when the tube is driven to clipping by transients.