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 Post subject: Anyone made temperature measurements inside radios?
PostPosted: Sep Sun 19, 2021 4:39 pm 
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Location: Monroe, NC 28112 USA
Anyone made temperature measurements inside radios?

So I have folks that are insisting that I re-stuff capacitors so they appear original. Folks have used all sorts of materials to fill the ends of the old paper sleeves. I see now that there are colored hot melt glues (Keratin glue sticks) that are available in a wide range of colors. But I've not seen any info to tell me if the glue will run/sag at the temperatures to be encountered under the steel chassis of a common 30s or 40s radio.

Has anyone already made a study of this?

I'd like to have a material that would remain sag free in said radios for say 8 hours with an ambient temperature of 80 F.

Comments welcome.

Robert


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 Post subject: Re: Anyone made temperature measurements inside radios?
PostPosted: Sep Sun 19, 2021 5:04 pm 
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Location: Carmel, Indiana
I don't know of anybody that has ever bothered to officially researched the temperatures inside antique radios. The heat generating factors vary from every make and model out there. It's generally accepted that it gets warm above the chassis where the tubes and transformers are and it rarely gets warm underneath the chassis. Now, there's always exceptions to this rule but this is generally how it is.

As far as restuffing caps, and I've restuffed a few of those 400v and 600v Sprague caps from Scott radios, I just use beeswax. That's what many cap manufacturers used back then, that's what's held up pretty well over these many decades, and that's what I choose to use today without any problem. For older caps such as metallic box capacitors from the 1920s, I just use recycled black tar from old 1920s tar filled electronic components.

If these folks are so demanding about destuffing capacitors, what do you do when having to replace some of those old resistors, especially the dogbone types. You can't restuff those, can you? I mean the underside is always going to look repaired to some extent. I can see restuffing the caps to, say, a Scott radio but not some cheap little Clinton radio.

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www.indianaradios.com


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 Post subject: Re: Anyone made temperature measurements inside radios?
PostPosted: Sep Sun 19, 2021 5:15 pm 
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I have a GE tombstone, A53 (but the Canadian version which had different veneer), where some time in the early 90s it was recapped and whoever did it restuffed the capacitors and used what appears to be a glue gun to seal the ends of the cardboard.

I had to recap it again due to it not working right, and the glue was all still holding strong and undistorted looking 30 years later.I had used it alot in the late 90s/early 00s so if any of the ones close to resistors were going to melt, it would have happened.


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 Post subject: Re: Anyone made temperature measurements inside radios?
PostPosted: Sep Sun 19, 2021 6:46 pm 
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Location: Near Brandon, Iowa
You can purchase high-temp hot-melt glue sticks that require a temp of 195 deg. F to liquefy (the more common craft-style stick melts at around 105 deg. F). It's likely that these high-temp sticks also require a special glue gun; but I'm not positive of that.


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 Post subject: Re: Anyone made temperature measurements inside radios?
PostPosted: Sep Sun 19, 2021 6:58 pm 
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Joined: Jan Mon 16, 2012 4:15 pm
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Location: Near Brandon, Iowa
Indiana Radios wrote:
...what do you do when having to replace some of those old resistors, especially the dogbone types. You can't restuff those, can you?


I've read of people carving "mold master" dummies of large dogbone resistors, then making silicone rubber molds of them. New resistors are inserted in the mold cavity and then casting resin is poured in, encapsulating the actual resistor. The part is finished by removing the mold parting lines and painting with a suitable body color, adding ID color spots per the original.

Obviously, this approach has some limitations (you'd have to choose a casting resin that could stand up to high heat if the resistor you were faking dissipated a lot of power; and the lead ends won't exactly duplicate those of the actual part). I personally think it's a waste of labor; but that's the restorer's call.


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 Post subject: Re: Anyone made temperature measurements inside radios?
PostPosted: Sep Sun 19, 2021 6:59 pm 
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Small slices of wooden ramin dowels (painted) will secure the ends of restuffed capacitors, if you are into that sort of nonsense!
Any diameter of dowel can easily be produced with a battery drill and a bottom cutter router jig. lol

:) Greg.


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 Post subject: Re: Anyone made temperature measurements inside radios?
PostPosted: Sep Mon 20, 2021 1:24 am 
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I've made reproductions of the larger size dogbone resistors using phenolic tubing and filling the ends with electronic potting epoxy and then painting.

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Who's that swimming in the punch bowl?
It's Walter Wart, the freaky frog!


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 Post subject: Re: Anyone made temperature measurements inside radios?
PostPosted: Sep Mon 20, 2021 1:33 am 
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What about using clay? It will dry but won't melt.

I use a laser thermometer on a chassis on the bench and often see 80 degrees F, such as at the base of a 50L6, and a high watt dropping resistor can go over 100 degrees. Small yellow caps and typical resistors under 1 watt don't get that hot unless there is a fault.

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Burl Ives, RIP, oldtimer.
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 Post subject: Re: Anyone made temperature measurements inside radios?
PostPosted: Sep Mon 20, 2021 2:22 am 
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I restuffed some few caps at work using epoxy. I used tape then paper filler in to take up alot of space since the mylar caps hardly can fill a paper tube. The epoxy mix we had was white. First I tried some brown paint on the epoxy ends and it looks plausibly authentic. Then I later left room and put beeswax in on the epoxy. That is authentic enough but nothing I would do regularly. Would be for a particularly special radio or application like someone said, or just practice ahead of time.

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 Post subject: Re: Anyone made temperature measurements inside radios?
PostPosted: Sep Mon 20, 2021 5:09 am 
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Location: British Columbia
I've only used the regular hot melt craft glue, but given that even the old paper caps inside radios are generally kept away from the big power resistors, in their original design, it's not really an issue. If your under chassis, or in cabinet temperatures are high enough to melt hot glue then you have a problem.
I haven't attempted to reproduce BED code or dogbone style resistors yet, but the guys that do usually use a one or two Watt rated resistors inside, there are ones that Vishay produces that are about the same size as the old 1/2 Watt carbon comp resistors from the 1940s-50s, and have a high voltage rating too. Even if you don't want to make a repro dogbone resistor with one the bodies are brown so they blend in with the rest of the old style components, as most new resistors do, other then those hideously bright blue ones.
Regards
Arran


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 Post subject: Re: Anyone made temperature measurements inside radios?
PostPosted: Sep Mon 20, 2021 2:53 pm 
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I haven't done exactly what you want. The SX-11 I am working on came to me with some evidence of a blown power transformer. So I carefully and slowly powered it up with the rectifier tube pulled and I monitored the lamination temperature with an IR thermometer while I was doing that. It checked out fine and the radio is almost completed. Oddly enough many of the original wax caps under the chassis had long "teardrops" of wax hanging down from them. Clearly this radio had lived in a warm environment at some point in its life. The restored radio does not get particularly warm on its own under the chassis so maybe some previous owner had set it up on a steam radiator or something?? The seller said he thought the radio had been pulled from a"ship" but who knows if that has any truth to it?


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 Post subject: Re: Anyone made temperature measurements inside radios?
PostPosted: Sep Mon 20, 2021 3:59 pm 
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Location: N. Palm Bch, Fl.
I use bees wax to restuff the paper caps and have had no melting except in the Zenith TO P/S area. Quit a bit of heat there with the power resistors and more if you add a power resistor to the diode. Only 2 paper caps there and the wax melts right out after it has been in the cabinet a while. Leaves a mess in the cabinet. You don't see this with the original paper caps, so they must have used something else. Yet you can empty the original insides with a heat gun on low.
There are a few videos on making Dog Bone resisters and some look damb close to original.

Freeman


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 Post subject: Re: Anyone made temperature measurements inside radios?
PostPosted: Sep Tue 28, 2021 1:58 am 
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Location: Westland, MI, USA
Not inside a radio per se, but inside a Pioneer SX-1010 stereo receiver under the power regulator board. Using a thermocouple input into my DMM. It was 70C ambient air temp just under that board - the board is mounted inverted - no wonder nearly all the caps on those went bad! So yes, caps are affected by heat but in your case as others have pointed out you should be fine with the beeswax. Only caution I would mention is not to use in close proximity to any large power resistor under the chassis, like the ones used to provide load ballast to the power supply and multiple voltage point taps.


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 Post subject: Re: Anyone made temperature measurements inside radios?
PostPosted: Sep Tue 28, 2021 5:44 pm 
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Location: Santa Rosa, CA
https://markal.com/products/tempilstik

In industrial labs (Westinghouse) we used Tempil Sticks to measure temperatures in equipment... until we got IR sensing devices.

Rich


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 Post subject: Re: Anyone made temperature measurements inside radios?
PostPosted: Sep Tue 28, 2021 6:07 pm 
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Location: Near Brandon, Iowa
I don't own any radios of which I would fit inside.


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