Miniature Power Resistors

[Vez]

Has anyone tried these small metal film power resistors. They are the size of normal 1/2 watt resistors. I'm thinking of using them as dropping resistors in the B+ in a guitar amp. Thanx.
https://www.digikey.com/product-det...ents/PR01000101002JR500/PPC10KW-1CT-ND/597177

 

[shelly_d]

Metal film is usually smaller for the same power dissipation. I have used them in a number of spots and as long as I had the rating correct for the circuit they worked just fine. I not notice any added noise and they have proved reliable in service. Vishay makes reliable stuff.

 

[Dave451]

Agree, but watch the maximum service voltage rating on some of these types. They may not be usable in higher-voltage circuits.

 

[arts]

I once ordered some by mistake.They work well,and have been reliable.If you do decide to go with these,keep them away from anything heat sensitive or combustible;you can almost light a cigarette off of them

 

[shelly_d]

Agree, but watch the maximum service voltage rating on some of these types. They may not be usable in higher-voltage circuits.

You are quite right. The one linked to is rated to 350V. They have other series that are good to 500.

 

[Vez]

You are quite right. The one linked to is rated to 350V. They have other series that are good to 500.

Thanks shelly_d for pointing that out. I believe the first node is about 430 volts. And thank everyone for replying.

 

[gadget73]

I believe its voltage dropped across the resistor that is the concern, not the voltage relative to ground.

 

[primosounds]

Has anyone tried these small metal film power resistors. They are the size of normal 1/2 watt resistors. I'm thinking of using them as dropping resistors in the B+ in a guitar amp. Thanx.
https://www.digikey.com/product-det...ents/PR01000101002JR500/PPC10KW-1CT-ND/597177

I also ordered some by mistake from Mousser. I will not use them in tube equipment and they are cheap so not an issue. If you see a very cheap 1watt or 2 watt resistor in the catalog they are probably this type. I don't believe they are designed for tube equipment (high voltage) so that is a real concern.

 

[dowto1000]

If they are cheap, and if they sound good, use two at double the value, in parallel.

You get two wire paths instead of one, and it will be more reliable and sound more dynamic, due to the two equal signal paths.

There will be a possibility of skewing of the sound, if the Rs are not tightly matched to each other. So, match to at least 1%.

I will match to 0.1% or 0.01%, on Ras and Rks, on my SET builds.

If you read Jeff Day's review of the French LEFSON speaker-crossover resistors, you will obtain a feel for what happens sonically, when you go from one set of leads on a resistor, to two runs of wire, and finally, to two equal and double the value Rs in parallel. Works !!

https://positive-feedback.com/audio...end-analog-audio-devices-the-lefson-resistor/

You'll deduce the advantages of paralleling CLOSELY MATCHED resistors ( each double the intended value) in a decent audio circuit.

I double - up resistors, in my own amp designs and builds. Matching needs to be spot on to avoid skews, and to avoid degrades.

NEVER series-connect Rs !!

Dowto1000

 

[x3workshop]

If they are cheap, and if they sound good, use two at double the value, in parallel.

You get two wire paths instead of one, and it will be more reliable and sound more dynamic, due to the two equal signal paths.

There will be a possibility of skewing of the sound, if the Rs are not tightly matched to each other. So, match to at least 1%.

I will match to 0.1% or 0.01%, on Ras and Rks, on my SET builds.

If you read Jeff Day's review of the French LEFSON speaker-crossover resistors, you will obtain a feel for what happens sonically, when you go from one set of leads on a resistor, to two runs of wire, and finally, to two equal and double the value Rs in parallel. Works !!

https://positive-feedback.com/audio...end-analog-audio-devices-the-lefson-resistor/

You'll deduce the advantages of paralleling CLOSELY MATCHED resistors ( each double the intended value) in a decent audio circuit.

I double - up resistors, in my own amp designs and builds. Matching needs to be spot on to avoid skews, and to avoid degrades.

NEVER series-connect Rs !!

Dowto1000

And if one of the two in parallel fails? Not so critical in a crossover, but in a tube amp circuit, quite possibly, no?


If you go with the 2 watt rating of this series they are rated for 500v and they are the size of a 1/2 watt MF. Data sheet below.

https://www.mouser.com/datasheet/2/427/pr010203-239785.pdf

 

[GordonW]

Higher-power rated resistors are, almost always, less noise than the lower wattage models of the same type.

Also, paralleling two identical resistors, will usually result in a reduction of noise, as well, compared to a single resistor of the same type, of half the resistance value.

I, also, will parallel resistors to get exact values (cancelling out tolerance errors) in critical places in a circuit. Stuff like cathode bias sense resistors on output tubes, feedback resistors, plate and cathode resistors in the first stage of an amp (the stage where the feedback connects), and preamp plate and cathode resistors, are sometimes candidates, if I can't find single ones that are matched well enough for the two channels.

Also, sometimes, I just need a non-standard value (this happens most often when tweaking feedback and compensation circuits, and sometimes to get correct bias or power supply voltage). Paralleling resistors can get you to exact values needed, when there's no one resistor that's exactly correct in value...



Regards,
Gordon.

 

[dowto1000]

And if one of the two in parallel fails? Not so critical in a crossover, but in a tube amp circuit, quite possibly, no?


If you go with the 2 watt rating of this series they are rated for 500v and they are the size of a 1/2 watt MF. Data sheet below.

https://www.mouser.com/datasheet/2/427/pr010203-239785.pdf

I have never had a R fail, in any amps I build, over the last 37 years. I use them at 25% of rated power typically.... never more than 1/3rd rated power.

Dowto1000

 

[x3workshop]

I tend to derate as well, but I have only 4 years experience. Good to know.

 

[GordonW]

I have never had a R fail, in any amps I build, over the last 37 years. I use them at 25% of rated power typically.... never more than 1/3rd rated power.

Dowto1000

Yep, 1/3 of rated power max, is my design goal as well.

Regards,
Gordon.

 

[Brice]

Also to keep in mind, increasing the resistor power reduces the thermal noise, especially in high gain stage, in the tube's plate and cathode.

 

[triode17]

If they are cheap, and if they sound good, use two at double the value, in parallel.

You get two wire paths instead of one, and it will be more reliable and sound more dynamic, due to the two equal signal paths.

There will be a possibility of skewing of the sound, if the Rs are not tightly matched to each other. So, match to at least 1%.

I will match to 0.1% or 0.01%, on Ras and Rks, on my SET builds.

If you read Jeff Day's review of the French LEFSON speaker-crossover resistors, you will obtain a feel for what happens sonically, when you go from one set of leads on a resistor, to two runs of wire, and finally, to two equal and double the value Rs in parallel. Works !!

https://positive-feedback.com/audio...end-analog-audio-devices-the-lefson-resistor/

You'll deduce the advantages of paralleling CLOSELY MATCHED resistors ( each double the intended value) in a decent audio circuit.

I double - up resistors, in my own amp designs and builds. Matching needs to be spot on to avoid skews, and to avoid degrades.

NEVER series-connect Rs !!

Dowto1000

Well I don't agree with what Lefson is saying. "It never ceases to amaze me how much changing even a single length of wire, a capacitor, a resistor, or an inductor in an audio circuit can influence the overall 'voicing' performance in terms of sonics & musicality...." Really? A piece of wire, come on.
Plus, just putting two resistors in parallel doesn't solve the voltage rating issue. Now both resistors are under strain, no?

 

[shelly_d]

Well I don't agree with what Lefson is saying. "It never ceases to amaze me how much changing even a single length of wire, a capacitor, a resistor, or an inductor in an audio circuit can influence the overall 'voicing' performance in terms of sonics & musicality...." Really? A piece of wire, come on.
Plus, just putting two resistors in parallel doesn't solve the voltage rating issue. Now both resistors are under strain, no?

I would agree, two in parallel does nothing about the voltage rating. IT does however drop the power being disipated in each. That will drop the temperature, which will reduce the amount of noise they produce.

Shelly_D

 

[FlaCharlie]

I believe its voltage dropped across the resistor that is the concern, not the voltage relative to ground.

I've always wondered about this when voltage ratings are brought up. But I always figured that the main thing is to derate in terms of power dissipation. If the wattage rating of the resistor is 4 or 5 times the power being dissipated, there shouldn't be a problem with reliability and the heat being generated should be reasonable.

Please correct me if there's a flaw in my thinking.

If you dig into the data sheet, yes you'll find a voltage rating. But the description of the resistor always just lists ohms and wattage.

 

[triode17]

If the wattage rating of the resistor is 4 or 5 times the power being dissipated,

It doesn't even need to be that high. The general rule is to double the power being dissipated.

 

[FlaCharlie]

It doesn't even need to be that high. The general rule is to double the power being dissipated.

So are both of these statements correct?

That the voltage rating refers to the voltage dropped across the resistor, not the voltage measured to ground. And that as long as the wattage rating of the resistor is at least twice the power being dissipated, the resistor is safe to use.