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 Post subject: RCA 8-T-243 Picture I.F. Transformers
PostPosted: Jan Wed 17, 2018 2:41 am 
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Posts: 57
I need to replace the slugs in the 2nd and 3rd pix I.F.'s in this set. It looks as if the tops of these cores crumbled to the point where the alignment tool slot is gone. Any tips on removing these slugs and finding replacements would be appreciated. Ideally a complete replacement I.F. would be the thing. The part numbers printed on these are 941151-1 and 941152-1. It's a Canadian made set so perhaps the part numbers aren't the same as similar USA sets.


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 Post subject: Re: RCA 8-T-243 Picture I.F. Transformers
PostPosted: Jan Wed 17, 2018 4:22 am 
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Joined: May Sun 07, 2017 11:35 am
Posts: 253
Here's how you can get the slugs out:

1. Wash slug and former thoroughly with alcohol so there's no wax, oil or grease left on the slug.
2. Get a plastic drinking straw (not wax paper) that's a snug fit in the coil former, and a wooden skewer, the type you use to hold a roast together. It must be wood, plastic will not work, and it needs to be a loose fit inside the drinking straw.
3. Mix some high strength, slow curing, 2 part epoxy. Dip the skewer in this so there's about 1/8" of glue on the end and slide it into the drinking straw.
4. Holding the straw and skewer with the glued end facing up. wipe any glue from the outside of the straw.
5. Insert the straw and skewer into the coil former, glue end still facing up. Push the skewer and straw in so that it's in contact with the ferrite slug.
6. Invert the whole thing so that the glue runs down the skewer onto the slug. Leave it a few minutes and jiggle the skewer up and down a bit.
The idea of the straw is to stop the glue bonding to the inside of the former.
7. Wait 24 hours or longer so a strong bond is formed.
8. You should be able to pull the drinking straw out so the skewer is left behind.
9. Turn the skewer and unscrew the slug.

You'll probably find there's a good adjustment slot on the other end of the slug, so you can invert and re-use it.
If there are two slugs, you can use an alignment tool that's a good fit in the slot to wind the other slug out from the other end. Reverse it, and it can be screwed back in.

This method works best on Thermoplastic formers, i.e styrene, polystryrene, acrylic etc. The kind of plastic that will melt. Epoxy does not bond well to these plastics.
If your coil former is a Thermoset plastic, i.e. phenolic, use extra care to ensure the epoxy does not get into the threads, i.e. use less epoxy and minimum time inverted. Epoxy bonds quite well to thermoset plastics.
How to tell? Touch it with a hot soldering iron. If it melts, it's a thermoplastic.

The other kind of coil former you see is paper phenolic. If the epoxy ends up sticking to the coil former, you can actually force the slug out using a hammer and drift, by stripping the pressed-in threads. You can "replace " the damaged threads with thin plastic sleeving or waxed twine. Just poke a short length down the former and screw the slug in so that the twine etc. is between the slug and the coil former wall.

Enjoy!


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 Post subject: Re: RCA 8-T-243 Picture I.F. Transformers
PostPosted: Jan Wed 17, 2018 5:11 pm 
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Joined: Mar Tue 03, 2009 11:12 pm
Posts: 1407
Location: Hutchinson KS
What I used to do "back in the day" was to use a jewelers screwdriver as a drill bit and bore a hole through the slug by using my fingers and let the slug crumble up and fall through the core. Of course this method requires finding a new slug.


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 Post subject: Re: RCA 8-T-243 Picture I.F. Transformers
PostPosted: Jan Wed 17, 2018 6:03 pm 
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Posts: 57
These transformers are not inside an aluminum can, but instead are 'out in the open'. They look to be constructed of black bakelite. I could try irob2345's method but a bit worried about the epoxy getting into the threads. My inclination has been to do the careful drill-out thing. Awhile back I found and purchased 3, NOS units of the exact same physical construction, (but not the exact same type) hoping that I could use the slugs if they are the same length as the existing ones. I haven't gotten to that point as I've been dealing with other issues with this TV. It's been a bit of a dog, but I'm determined to get it going.
Thanks for the tips, gentlemen.


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 Post subject: Re: RCA 8-T-243 Picture I.F. Transformers
PostPosted: Jan Wed 17, 2018 6:47 pm 
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Joined: Mar Sun 01, 2009 10:27 pm
Posts: 4485
Location: Ann Arbor, MI
Just a thought. If you have a skewer glued to the slug and can unscrew the slug, why not leave the slug in the coil and adjust it with the skewer?

_________________
Tom


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 Post subject: Re: RCA 8-T-243 Picture I.F. Transformers
PostPosted: Jan Wed 17, 2018 6:58 pm 
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Duh, yes! Haha
Good point, Tom!


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 Post subject: Re: RCA 8-T-243 Picture I.F. Transformers
PostPosted: Jan Thu 18, 2018 1:44 am 
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Joined: May Sun 07, 2017 11:35 am
Posts: 253
Of course Tom you are right.

The last time I used this method though was on a ratio detector transformer which had two slugs. Both were gouged due to an attempt by someone years back to fix it when the real fault was a bad germanium diode. So I had to get both slugs out. Only had to do the glue trick on one end, once I got one slug out I could get to the unmolested underside of the other one (sounds rude).

But in this case leaving the stick in place wasn't an option, the underside of the ratio detector was buried deep in the chassis and the top side is up against the bulb of the CRT.


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