1/4w resistors vs 1/2w for preamp plates

[fossilshark]

Accidentally ordered 1/4w 220K resistors instead of 1/2w that the schematic calls for. For plate resistors on 12ax7s will this be a problem? This amp is just being repaired for a friend in a bit of a time crunch.

[shooter]

(voltage across the plate R ) * ~~~~~ .0015A (about what an AX draws at idle) = power in Watts

[stratomaster]

What's the voltage rating of the resistor?  That's the real question.

[Merlin]

Most 1/4W resistors are only rated for 200V, which is probably not enough. I suspect you're gonna need 1/2W.

[fossilshark]

If Merlin says so then it is. I will order 1/2w replacements. Thanks for the advice!

[kagliostro]

Since I suffer from deforming arthritis in my hands and I am also short-sighted, my preference always goes to nice 2W metal film resistors, which, to be honest, have a look that is more reminiscent of the size of old carbon-bond resistors among other things, even if they were not metal film, 2W resistors are "quieter" than the same type of 1/2W


Franco

[fossilshark]

I will have to see what I can find that will fit in the PCB. Maybe some of vishays ceramic resistors at 1w would be good.

[scstill]

An interesting read...
https://el34world.com/Forum/index.php?topic=26399.0

[AlNewman]

Here's a good quote from PRR from the linked thread.

"You can't burn-up even a 1/4W in grid or cathode service.

If a preamp tube goes dead-short, a 100k plate resistor on 300V supply gets 0.9 Watts.

Toasted carbon-comp is bad mojo, always over-size for reliability."