I'm shopping for resistors to repair a preamp. The specs in the schematic describe the composition, resistance, tolerance, and temperature coefficient in PPM / C. They do not specify the power rating. Is there a way to derive the power rating from the information given?
No, but do you know the DC voltage normally across the resistor?
Is there significant signal or power 60Hz or 120Hz voltage across it?
Maybe it's best to post the schematic.
Is there significant signal or power 60Hz or 120Hz voltage across it?
Maybe it's best to post the schematic.
The physical size and composition pretty much fix the power rating.
I have never seen temperature coefficient specified in a preamplifier - hardly likely to be sensitive. In HiFi, only active filters are at all fussy.
I have never seen temperature coefficient specified in a preamplifier - hardly likely to be sensitive. In HiFi, only active filters are at all fussy.
See attached schematic (ignore highlights). I'm interested in the resistors that may cause noise in the phono circuit, which I think include R64, R73, R70/71. I've alas attached a picture of the board where I've started labeling resistors. There seem to be two main sizes, one around 8mm and one around 12mm (or so, my measurement technique was pretty vague).
Mostly I'm just concerned about getting the right size parts so they fit nicely in the spot. I suppose I could just measure, but I thought, if there was an easy way to work out the rated power, that might make it easier.
Mostly I'm just concerned about getting the right size parts so they fit nicely in the spot. I suppose I could just measure, but I thought, if there was an easy way to work out the rated power, that might make it easier.
Attachments
Those parts will not dissipate much power. Also, different brands of the same power rating can differ in size.
Measure the part mounting holes center to center spacing. To measure the spacing accurately, use a 1" long resistor lead offcut,
and bend it to drop right into the two holes.Then take it out and measure carefully.
Subtract a total of 0.2" (or 5mm) to allow for not cracking the end coating during lead bending, which will cause real problems,
and that is the longest resistor body length that will fit properly. When stuffing, use a proper lead bender to form the resistor leads.
Measure the part mounting holes center to center spacing. To measure the spacing accurately, use a 1" long resistor lead offcut,
and bend it to drop right into the two holes.Then take it out and measure carefully.
Subtract a total of 0.2" (or 5mm) to allow for not cracking the end coating during lead bending, which will cause real problems,
and that is the longest resistor body length that will fit properly. When stuffing, use a proper lead bender to form the resistor leads.