bias resistor location

[joesatch]

difference between resistor before diode vs resistor after diode?  Which one is correct?

[stratomaster]

Functionally identical. Practically different. What's the voltage rating of the diode? If you're taking bias off the HT line, you'll want the resistor first unless you're using a suitably voltage rated diode. Lots of modern designs use a 1N4003 in this spot.  Full HT would rapidly degrade that diode.

[joesatch]

1000v diode.  PT has a bias tap so 60VAC it delivers

[HotBluePlates]

...  Which one is correct?

Both, as long as you get the bias voltage you need.

[Merlin]

If you're taking bias off the HT line, you'll want the resistor first unless you're using a suitably voltage rated diode. Lots of modern designs use a 1N4003 in this spot.  Full HT would rapidly degrade that diode.

It still doesn't make any difference, the diode sees exactly the same reverse voltage either way. Kirchhoff's law, innit.

[pdf64]

In series circuits, component order makes no difference.

[stratomaster]

If you're taking bias off the HT line, you'll want the resistor first unless you're using a suitably voltage rated diode. Lots of modern designs use a 1N4003 in this spot.  Full HT would rapidly degrade that diode.

It still doesn't make any difference, the diode sees exactly the same reverse voltage either way. Kirchhoff's law, innit.

You're absolutely right. AC. Brain fart. Was stuck on DC, but then they'd be no reverse voltage to consider.

[HotBluePlates]

... the diode sees exactly the same reverse voltage either way. Kirchhoff's law, innit.

... Was stuck on DC, but then they'd be no reverse voltage to consider.

"Kirchhoff" is key:  See Kirchhoff's 2nd Rule, and notice that a series circuit is a closed loop with only 1 path.  The components that make up that closed path divide the voltage the same way, regardless of what order those components are arranged around the loop.

Add to that when the diode is reverse-biased, there is no current and so zero voltage-drop across any of the resistors.  The diode always sees the same reverse-voltage no matter where it is placed in the circuit relative to the resistors (that are dropping no volts at that moment).