My CTC-16XL Project.

[Electronic M]

Originally Posted by Yamamaya42

The resistor info for the resistor off the vert out cathode is a bit confusing.
The SAMs schematic shows r106 to be 5.6k 3w, with alt parts of irc resistor pw5-6000 6k 5 watts, & workman 3g-5600 ( 5.6k 3w)

The CTC-16 (not x) shows it to be 5w.
both have the same RCA part # for the resistor, 104180.
But the SAMs for the XL clearly shows 3w, and lists a part # shown on others listed as 5w, so what is in it? Does it not matter?


edit---
https://imgur.com/UbSRwgB
what i find so confusing
r106 vs 105 16xl- 16
same location on schematic, shows same RCA part number, why is one 5w and one 3w

If you can't spec the same wattage resistor always go up in wattage not down...they probably did that.

Also when replacing a high watt power resistor that tends to get hot in a restoration scenario it may be better to choose a higher wattage part than original as that will make the replacement run cooler.

[Tomcomm]

If you can't spec the same wattage resistor always go up in wattage not down...they probably did that.

Also when replacing a high watt power resistor that tends to get hot in a restoration scenario it may be better to choose a higher wattage part than original as that will make the replacement run cooler.

[tubesrule]

How does using a larger wattage resistor make it run cooler when the exact same wattage will be dissipated in it based on the usage? Other than the larger wattage resistor may or may not have slightly more surface area (unless you are changing to a chassis/heatsink mounted type or greatly increasing the physical size), it will run at the same temperature. The thermal resistance in free air will not be that much different and that, along with the watts dissipated is what determines the temperature.

[old_coot88]

Originally Posted by tubesrule

How does using a larger wattage resistor make it run cooler when the exact same wattage will be dissipated in it based on the usage?

For a given wattage being dissipated, x amount of heat is being dispensed thoughout the entire mass of the resistor. The greater the mass, the lower the temperature of a unit volume of that mass. Ergo, a larger mass runs cooler. Er, at least that's my hillbilly take on it.

[tubesrule]

Originally Posted by old_coot88

For a given wattage being dissipated, x amount of heat is being dispensed thoughout the entire mass of the resistor. The greater the mass, the lower the temperature of a unit volume of that mass. Ergo, a larger mass runs cooler. Er, at least that's my hillbilly take on it.

Mass has nothing to do with terminal temperature. Mass will affect the rate of change of temperature, but thermal resistance is what determines the terminal temperature. Thermal resistance is affected by material, surface area and air flow. A larger mass will make it take longer to reach its final temperature, but that temperature will still be the same.

[Electronic M]

Originally Posted by tubesrule

Mass has nothing to do with terminal temperature. Mass will affect the rate of change of temperature, but thermal resistance is what determines the terminal temperature. Thermal resistance is affected by material, surface area and air flow. A larger mass will make it take longer to reach its final temperature, but that temperature will still be the same.

Higher watt resistors typically have more surface area and thus run cooler...this goes for both chassis mount and non-chassis mount types.

A resistor of a given material typically gets rated by the amount of watts it can continuously handle without burning up or changing value (minus some percentage for headroom/safety). If the power put in is less than the power leaving that energy stays with the part and makes it hotter. If we concern our selves with a single resistance value and consider resistors of the same composition but different wattage rating, then obviously the higher rated part has a case that allows it to put energy into the air at a higher rate.
If a resistor is capable of putting thermal energy into the air at a higher rate than the circuit can supply it with energy the it will not store thermal energy and stay cool....
This can be proved empirically by taking a 1/2, 1 and a 10W resistor all of the same resistance connecting them in turn to a bench supply set to deliver 1W of power to them and observing how each responds over say 1 hours time...the 1/2W should over heat and burn open, the 1W probably get too hot to touch but remain stable and the 10W probably won't get noticably warmer than the ambient temperature of the room..... I've performed a version of this experiment before.

[tubesrule]

Tom
You just repeated what I said. Wattage rating has nothing to do with terminal temperature. Thermal resistance does. For example, modern metal film 1W and 2W resistors are smaller than older 1/2W carbon comp resistors because they are designed to run hotter (better materials) and do run hotter because they are smaller (higher thermal resistance). So in this case, a physically smaller resistor is a better choice for reliability even though it will run hotter at the same power dissipation as the larger 1/2W comp resistor.
If you want to state that a higher wattage resistor that is the same composition and much larger in physical size will run cooler, that is a true statement, but only because its thermal resistance is lower, not because its wattage is higher. The two are not absolutely related or interchangeable.

[old_coot88]

Originally Posted by tubesrule

Mass has nothing to do with terminal temperature. Mass will affect the rate of change of temperature, but thermal resistance is what determines the terminal temperature. Thermal resistance is affected by material, surface area and air flow. A larger mass will make it take longer to reach its final temperature, but that temperature will still be the same.

But only in a hypothetical where the mass is totally insulated against radiative and convective cooling. In the real world, the larger mass, having greater radiative surface and more surface exposed to airflow, will end up running cooler than a smaller mass dissipating the same wattage. Seems like, anyhow.

OOPs. Electronic M already done it.

[tubesrule]

Originally Posted by old_coot88

But only in a hypothetical where the mass is totally insulated against radiative and convective cooling. In the real world, the larger mass, having greater radiative surface and more surface exposed to airflow, will end up running cooler than a smaller mass dissipating the same wattage. Seems like, anyhow.

OOPs. Electronic M already done it.

Surface area is separate from mass. Just because something is higher in mass, it does not have to have more surface area. If you take a hollow tubular vitreous power resistor and fill it solid, you have greatly increased the mass, greatly decreased the surface area and greatly increased the thermal resistance. The resistor will then run hotter.