My CTC-16XL Project.

[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.

[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]

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.

[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.

[Electronic M]

Originally Posted by 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.

I was never trying to say that 2 different composition parts will have the same thermal resistance for a given wattage rating when you started arguing. Merely stating that if you are going with some wattage in a given composition part that choosing a higher one than necessary tends to reduce case temperature...You're very passionate about arguing an accurate generalization deep into the weeds.

[tubesrule]

I was responding to your original comment which was inaccurate and who's goal posts have now been moved several times. Sorry I wasted time on the forum. It won't happen again. Carry on.

[Yamamaya42]

I did not mean to start a huge fight T_T
I was just confused by seeing the same RCA# and dif watt values.

What i'd really like to know now is, where do you guys find all these vintage sets
I know i was was lucky to find my 16xl all those years ago and protect it.

but i really don't want to put the effort into the CTC-90 i have, it;s a weird model and solid state, but had a NEW CRT. if i could track down a CTC-17 (or something like) to play with, then i would find more interest for it.

[Electronic M]

Originally Posted by Yamamaya42

I did not mean to start a huge fight T_T
I was just confused by seeing the same RCA# and dif watt values.

What i'd really like to know now is, where do you guys find all these vintage sets
I know i was was lucky to find my 16xl all those years ago and protect it.

but i really don't want to put the effort into the CTC-90 i have, it;s a weird model and solid state, but had a NEW CRT. if i could track down a CTC-17 (or something like) to play with, then i would find more interest for it.

There are plenty of places online where vintage TVs are for sale, there are also collector clubs for radios (also the ETF) and some places like antique stores and thrift shops where chances of finding sets are good.
You also, depending on where you live, may have to be willing to drive sometimes hours or wait years if you want something specific that isn't super common...Large old population centers where there was money when the sets were new and where there (are at least pockets where there) hasn't been a lot of population churn or redevelopment/modernization are usually places where people can easily find vintage sets locally...Places like Chicago, Milwaukee, Detroit, the larger cities on the east coast, LA, etc. seem to always have enough available to start a decent small collection in a couple months. Places like deep rural Idaho you might not ever find anything if you limit your search to a 2 hour drive.
Some of my better finds I had to drive around 6 hours 1 way to get...And a good portion of my collection has come from driving from Milwaukee to Columbus Ohio 1-2 times a year for the ETF meet.

BTW: don't sweat the little arguement. That is relatively mild in the context of what all I've dealt with over the years here (and I only slightly bothers me)...While by and large the TV community is a bunch of extremely good folks (and thousands of times better mannered than some internet message communities) I have met some bad apples, who have lied, picked fights with me, intentionally grabbed sets I was on my way to buy, cheated me out of money for things, etc, etc...The most sought after stuff (Pre-WWII, some early post-war models ad pre-1960 color) can bring out the worst in people when for sale, and some folks can be or come across as just plain rude (I've made that mistake) when correcting others on details or recieving corrections on their details.

[Yamamaya42]

That did not work too well.

I tried to wire in a IF section bypass switch at TP1 ( point B) by running a video wire from one end of L9 to a switch on the back of the set and back to the grid of the first video amp, so I could switch between Ext video and video from IF, but the Tuner video was too washed out/ weak, I guess the video lines too and back from the switch added too much resistance for the IF input to work correctly.

External input works great though!

Next time I have the chassis out, I will just have to stick a relay at that point to get it to do what I want, same with the Audio,

Right now with ext video, I tap audio into the volume control R1 at point 30,( V8 Removed ) but I have to boost it by several Dbs or it wont be loud enough , pulled down by inactive sound circuts through c53, I'm sure if I also put a relay to switch in audio and cut out that cap, I wont have to boost it so much.

[old_tv_nut]

Originally Posted by Yamamaya42

That did not work too well.

I tried to wire in a IF section bypass switch at TP1 ( point B) by running a video wire from one end of L9 to a switch on the back of the set and back to the grid of the first video amp, so I could switch between Ext video and video from IF, but the Tuner video was too washed out/ weak, I guess the video lines too and back from the switch added too much resistance for the IF input to work correctly.
...

Not likely a resistance problem, but too much stray capacitance with the long wires. A relay would still be the fix.

[Yamamaya42]

Originally Posted by old_tv_nut

Not likely a resistance problem, but too much stray capacitance with the long wires. A relay would still be the fix.

It's also probably best to get the right KIND of relay, power vs signal, though in this case may not be ultra critical, it still may make a difference. Choosing, Mouser 653-G5V-1-DC12 when I DO plan to do it, I already have the +12v from my video amp.

[Yamamaya42]

someone got lucky

https://www.ebay.de/itm/RCA-113992-F...-/202797172756

I want one as a spare, just in case :/

[Yamamaya42]

I can see now see why these are better than the original RCA FBTs

https://imgur.com/4QcPFRc

But what blows my mind even more, is that it went for $75 and the seller did not overcharge for it

but damn!
I check every month to see what is out there ... and that one sold on 10/20

I should check more often T_T