I'm about to order the parts for the Honey Badger class AB amplifier and I want to use vishay dale resistors. According to the datasheets of CMF55/RN55, the two variants are physically identical, except of the military standard ratings of the RN55. Looking at the datasheet of CMF55, one can see that it handles .5w for an ambient temperature of 70C. Does that mean that I can use CMF55/RN55 resistors in circuits that require .5w resistors? Also, if you take a look at the RN55 datasheet, a power dissipation of .125w is stated for Tamb=70C. I'm a bit confused and I don't want to order a bunch of resistors and watch them burn, so could you please help?😕
The RN-series resistors are underrated, so a .25W resistor is in fact a .5W resistor.
Be aware that this has an impact on their size, too! (They‘re mostly actually of the next form-factor, too... I learned this when I built a bugle2 Phono-pre with them, and had to insert them „soldier-style“—upright in alternating positions)
Be aware that this has an impact on their size, too! (They‘re mostly actually of the next form-factor, too... I learned this when I built a bugle2 Phono-pre with them, and had to insert them „soldier-style“—upright in alternating positions)
That's what confuses me. Some people say that the "true" value of RNs is 2 times the military value, but according to the CMF55 datasheet it is 4 times (0.5w = 4*0.125w).
Stick to the datasheet, then.
(Or not, as long as the parts fit the board—aren‘t too long, too thick or the legs don’t fit the hole on the board—overrating a resistor by a factor of 2 or 4 is not a problem
(Or not, as long as the parts fit the board—aren‘t too long, too thick or the legs don’t fit the hole on the board—overrating a resistor by a factor of 2 or 4 is not a problem
It depends on a needed parameters. We may 'rate' 0.25 W resistors as 0.5 W or 0.125 W, or 0.05W dependably on needed accuracy with temperature etc.
If they burn, who dies?
In MILITARY use, lives or even a kingdom may be lost if a resistor burns. Also the soldiers have to go into hell (or a desert) if that's what it takes. You are not going to be listening to records in 70C; even inside a tube amp that is quite high. At 60C the resistor life is about 10X.
From the CMF datasheet (emphasis mine):
Vishay Dale Model CMF is also available as Military Qualified Styles RN and RL. See Vishay Dale’s CMF (Military RN and RL) datasheet (www.vishay.com/doc?31027) for the MIL-SPEC ratings / attributes. (Except for marking, the Industrial and Military versions are exactly the same).
If you are using the resistors for non-military use, use the CMF ratings. For an RN55, this is the same as a CMF55, 0.5W at 70ºC. They are the same size and color. Same goes for CMF60/RN60, etc.
It probably doesn't matter for most DIY use, but these resistors (all varieties) have some of the least consistent pricing that I've seen for any component. When buying quantities of 100, I regularly see one value range from less than $0.10 to over $0.50. If you do need a bunch of CMF55/RN55, I recommend checking several vendors if you're using parametric searches and cutting off the packaging codes and varying tolerance codes if you're using an aggregator like Octopart.
Vishay Dale Model CMF is also available as Military Qualified Styles RN and RL. See Vishay Dale’s CMF (Military RN and RL) datasheet (www.vishay.com/doc?31027) for the MIL-SPEC ratings / attributes. (Except for marking, the Industrial and Military versions are exactly the same).
If you are using the resistors for non-military use, use the CMF ratings. For an RN55, this is the same as a CMF55, 0.5W at 70ºC. They are the same size and color. Same goes for CMF60/RN60, etc.
It probably doesn't matter for most DIY use, but these resistors (all varieties) have some of the least consistent pricing that I've seen for any component. When buying quantities of 100, I regularly see one value range from less than $0.10 to over $0.50. If you do need a bunch of CMF55/RN55, I recommend checking several vendors if you're using parametric searches and cutting off the packaging codes and varying tolerance codes if you're using an aggregator like Octopart.
Well, I decided it's not worth the trouble and the money. I think I'll just get some KOA Speer MF series resistors. They seem to be just fine for me project's requirements. What is your opinion on them? Do you have any other suggestions for a high quality metal film resistor?
My approach is usually (besides drooling over some exotic stuff from time to time) to first of all stick to the bom (if specific brands are noted, I go with them), then make sure the parts are good enough (tolerance, wattage etc) and, if there’s alternatives, choose what looks good with the board (although the vishays are dead-ugly, colorwise)
OK then, I will buy exactly what the bom says. However, most of the resistors are available only at digikey and not mouser, so I will substitute them with the KOA Speer MF series parts.
In audio, you are primarily interested in linearity and noise :
https://linearaudio.net/sites/linearaudio.net/files/CB-to-ES-V1-ref-3-IMG_0003.pdf
https://convexoptimization.com/TOOLS/SimonVishay.pdf
Cheers,
Patrick
https://linearaudio.net/sites/linearaudio.net/files/CB-to-ES-V1-ref-3-IMG_0003.pdf
https://convexoptimization.com/TOOLS/SimonVishay.pdf
Cheers,
Patrick