Resistor worries.

[joesatch]

ordered some metal oxide 2W resistors. i see they have a limit of 350V.  My B+ is over 400 volts. what do i do in this situation?

[sluckey]

Ignore the voltage rating.

[shooter]

^^what he said


pretty sure you won't be dropping 350V across the resistor, 50-60v maybe

[acheld]

I avoid TE Connectivity if possible due to variance and mislabelling (not common, but I've seen a half dozen instances in the past 4 years).

KOA Speer seems more reliable and has higher voltage specs.

I know it's not considered "correct," but I will use Vishay metal film resistors in some portions of the power supply.  Not suggesting this as best practice . . .

[joesatch]

I avoid TE Connectivity if possible due to variance and mislabelling (not common, but I've seen a half dozen instances in the past 4 years).

KOA Speer seems more reliable and has higher voltage specs.

I know it's not considered "correct," but I will use Vishay metal film resistors in some portions of the power supply.  Not suggesting this as best practice . . .

this makes me angry. i was under the impression Koa were the cheapest. So my order has already shipped. I'm very displeased

[shooter]

welcome to the 21st century 

[acheld]

this makes me angry. i was under the impression Koa were the cheapest. So my order has already shipped. I'm very displeased

a) Life's too short for that.   
b) Just my opinion (and many might not even agree !)
c) I use a fair number of KOA Speer power resistors, so far so good. Not sayin' they're the best, but have been ok for me so far.
d) No one except you, me, and Shooter will know
e) And it will all work out . . .

[pdf64]

^^what he said


pretty sure you won't be dropping 350V across the resistor, 50-60v maybe

At power up, the surge voltage across HT droppers can approach the full HT voltage.
Hence I suggest that a resistor type with voltage rating of the HT volage is selected.

As I've learned the hard way, some power resistor types might only have a 250V rating, these might fail in this application.

[stratomaster]

pretty sure you won't be dropping 350V across the resistor, 50-60v maybe

I'm having trouble internalizing this concept of a 'voltage rating'.  The maximum voltage drop across a specific resistor would be determined by its resistance and power rating.  The voltage rating must mean something other than "do not drop more than voltage rating across resistor". 

Furthermore, ratings like this are usually set under very specific conditions (temperature, humidity, etc) and are therefore subject to derating if you know the curve/formula to derate to other conditions. 

Until I understand further I'm in the "ignore" camp only because I've never seen a resistor failure that I could attribute solely to exceeding its voltage rating.  Always there was a short of another component nearby that caused over dissipation.  Maybe I've just been lucky.

[Merlin]

I'm having trouble internalizing this concept of a 'voltage rating'.  The maximum voltage drop across a specific resistor would be determined by its resistance and power rating. 

You'd be right if it weren't for transients. Power rating is for continuous dissipation, but it's still OK to exceed it on transients, when the voltage across the resistor is momentarily higher -but not beyond the voltage rating.

[joesatch]

i might toss these. even the mouser invoice says 350v.

[tubeswell]

But if they’re doing jobs where they’ll never see 350v, they’ll be fine. Lots of 1/2W resistors in lots of amps only have a 350V rating. (Leo’s schematics have a standard note stating ‘all resistors are 1/2W unless otherwise specified’, those are all 350V rating. Lots of commercially made tube amps have 1/4W resistors - and those only have a 250v rating).

[Willabe]

Don't throw them out. Even if you don't want to use them in a build, you can use them just to temp something your trying with gator clips.