I am currently in the process of (attempting) to restore a 1949 RCA T-100. When I got the set home, pulled out the chassis, and started testing and marking off weak tubes, I noticed that the black plastic base of the CRT (the part with all the pins) was coming loose. I went to bed, and woke up this morning to find the black base sitting on the chassis and what I presume to be the evacuation tip where the base was late last night. I have an inkling my Dachshund is to blame . . . Anyway, the 5 leads from the tube (Numbers 1, 2, 10, 11, and 12) are still intact. In fact, I have about a solid 1 to 1.5 inches to work with. If I were to rewire the leads to the base, and then reattach the base with RTV silicone or something similar, is there a chance that the tube could be salvaged? :dunno:

Thanks,
Benny

I assume you don't mean the evacuation tip is broken. If it's intact there's still a chance the 12LP4 is good.

Elves probably started to repair the base for you and got chased away by your Dachshund. Actually, if he did knock it off he did you a favor because it couldn't have been soldered on very well.

One method I've read on this forum is to attach small gauge wire to the leads to make it easier to thread the socket back on.

John

I am currently in the process of (attempting) to restore a 1949 RCA T-100. When I got the set home, pulled out the chassis, and started testing and marking off weak tubes, I noticed that the black plastic base of the CRT (the part with all the pins) was coming loose. I went to bed, and woke up this morning to find the black base sitting on the chassis and what I presume to be the evacuation tip where the base was late last night. I have an inkling my Dachshund is to blame . . . Anyway, the 5 leads from the tube (Numbers 1, 2, 10, 11, and 12) are still intact. In fact, I have about a solid 1 to 1.5 inches to work with. If I were to rewire the leads to the base, and then reattach the base with RTV silicone or something similar, is there a chance that the tube could be salvaged? :dunno:

Thanks,
Benny

Removing all the solder from the pins on the base is a necessary first step in saving your 12LP4.
If you heat the pins one at a time and then quickly smack the base on your work bench while the solder is still molten, this will effectively remove all the solder from each pin.
You should be able to carefully finesse each wire back into the base. Glue the base to the neck making sure each wire is fully inserted in each pin, I use Elmer's. Allow 24 hours for the glue to set.
Finally, with the tube face-down, solder each pin, removing your iron the instant the solder starts to flow.
Good luck.

I think the T-100 uses a 10BP4, the T-120 uses the 12lp4.
Same base pins.

An easier way to do this is to use some fine wire, like strands from a line cord. Solder a 6 inch length of a strand to the end of each lead coming from the CRT. Make sure the solder joint is small enough to go through the holes in the pins on the base. Now you can easily thread each strand through the appropriate pin. Once all are threaded, put some glue on the base, and pull the base onto the tube and solder each pin. As you do this, you can remove the strand.

You might want to test the CRT first to see if it's worth the trouble. If it's no good you could do the repair anyway just for practice.

good luck

You might want to test the CRT first to see if it's worth the trouble. If it's no good you could do the repair anyway just for practive.

good luck

How do you test the CRT before the plug is attached?

If you have a "universal" adapter for your CRT tester, it has leads that you can clip on in any possible pin configuration - so you don't need the base. You can easily make your own with some sort of clip (alligator, probe-type, etc), wire, and a tube base from a dud tube or brightener.

If you don't have a CRT tester, you can still use an ohmmeter to check for continuity between the filament pins. Infinite resistance means the filament is burned out and the tube's a dud. Resistance of a few ohms means the filament is intact (and most likely, the tube holds vacuum, since the filament would quickly burn out if powered up when vacuum was lost).

My T-100 uses a 10BP4. For that tube, or a 12LP4 for that matter, the filament pins are 1 and 12.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

Just re-tin the last 1/4 to 3/8 inch of the leads and don't move them. Keep the heat away from the glass. Gently position them so they will naturaly fit into the pins and re solder. A small clean piece of copper wire will help wick the solder into the pin. If silicone seal is used to secure the base use sparingly and keep off the wires as the acetic acid from curing is not a friend to wire. If the tube turns out to be bad for some reason the would be very good practice anyway.

If you have a "universal" adapter for your CRT tester, it has leads that you can clip on in any possible pin configuration - so you don't need the base. You can easily make your own with some sort of clip (alligator, probe-type, etc), wire, and a tube base from a dud tube or brightener.

Ah ok, I was thinking of a full dynamic emissions test. Erm, clipping things on the leads and playing with them will damage the leads, potentially breaking them. Since the socket has just naturally fallen off due to dry solder I'd put it back together first. - A bit of work that MIGHT be not worthwhile, but will be safest to do straight away.

You do have a good point- if the leads are in such bad shape that the socket just falls off, you're better off doing the repair first :)

Thanks guys, but the filament is bad. Looks like I'm in the market for a 12KP4 . . .

Sorry to hear that... Hope you have some luck finding a replacement!

Turns out the filament WASN'T bad, I'm just stupid when I'm tired. Bad news is that two of the leads on the picture tube have fallen off, and the other three are INCREDIBLY fragile. What can I do, if anything, at this point, besides buying a new picture tube (which wouldn't be half bad at this point . . .)?

Someone in another thread had some luck with conductive silver epoxy, especially if they're snapped off too close to the glass to easily solder to.

If the leads are straight, maybe giving them a coat of that would help?

I'm looking at epoxies, and I can't figure out how hot the neck of a 12LP4 would get during operation. I'm assuming much hotter than 40 degrees centigrade. Am I right?

Yep. Temps probably get somewhere similar to your average light bulb, considering the tubes also have black-body radiation coming from the filament.The leads/glass themselves will of course get nowhere near as hot. I think if you can get something rated for over 150 deg. C you should be ok; the solder usually begins to soften around 200 (and melts at 250), and you don't want to go anywhere near that during normal operation.

The epoxy is going to be on the glass, serving as an alternate lead. What temp. rating should I be looking at?

I guess I don't understand your previous message VintagePC.

Anything at or over 150 should do the job. (Yeah, it was kinda buried in the middle of the post :) )

Thanks. I was actually looking at this paint (http://www.semicro.org/silverpaint-18silver15g-1.aspx). My idea is to drop a little bit of the paint where the lead is surrounded by glass, then soldering the new lead to the dried paint. I'd then take some heat shrink tubing and wrap up the whole she-bang to prevent arcing. Finally, I'd wrap up the old leads, then thread on the socket and use a heat resistant adhesive to hold the base on. Solder the base's leads and call it good.

You might want to look at the method Phil Nelson ended up using on his Capehart's CRT. Down around post# 57 onward..
http://www.videokarma.org/showthread.php?t=251233&page=4

You won't be able to solder to the paint. They usually have an acetate base or similar which will decompose when you try to solder to it. Then the silver will just fall off of the glass.

The epoxy repair that I did on my Capehart's CRT seems to be holding up, although I haven't powered the tube for more than about 15 minutes altogether, so far. The advantage of the silver-filled epoxy is that it makes a strong physical bond as well as an electrical connection.

Phil Nelson

I wonder if it's possible to make your own conductive epoxy?

I know an old trick if you need thermal epoxy is to just mix heatsink paste+epoxy and it works quite well for general purpose.

Be interesting to see how far you'd get if you got some really fine metal powder and mixed it with epoxy.

Isn't J-B Weld epoxy with metal powder mixed in ? I don't think it's very conductive though :scratch2:

I think you should solder to it even if you have to use hair thin wire from an i.f. coil it will still have less resistance than using an epoxy, or epoxy conductive glue. You can do it with a fine point solder iron, and good rosin cleaner. And the thin wire will not torque the solder joint too much at all as you remount the plug base. Even if you have to get a dremmel tool with a pointy thing on it and dig out some of the glass around the broken wire. Wear a face mask and do it in the garage.

I don't think JB Weld is very conductive, if at all. I have used it to repair phenolic switch wafers that were damaged by B+ arcing.

The silver conductive epoxy is designed for electronic repair. Suggested uses include repairing PC boards.

Phil Nelson

http://antiqueradio.org/art/Capehart661-PSilverSolderEpoxy.jpg

http://antiqueradio.org/art/Capehart661-PCRTLeadRepaired.jpg

The silver epoxy is good stuff. While it has a higher resistivity than copper wire, it's still negligible. It adheres really well too. The normal heat from operation of the CRT isn't going to hurt it either.

had a regular customer who was told the crt in their year old quasar portable had a open heater.this was one of the matsushita built units with the new at the time ge inline tube.so no easy swap from a junker.heaters open?no one of the heater pins came out of the glass!wasnt arcing so i knew it had not gone to air.i took some duro 2 part epoxy and loaded it with fine silver powder that came from a friends work.they made conductive ink.
put a dab in the spot the pin used to be in then dunked the pin in the mixture.stuck it in and waited overnight for it to cure.put the plastic guide back on with silicone.fired it up and it worked.she used it 8 years before it went weak.
those tubes were not great anyway so who knows if it had a leak there.got the strangest look from my dad and his hunting buddy while i was doing this.nobody there thought it would work.
when it did and it had played overnight they were very surprised.i was 15 at the time.
The silver epoxy is good stuff. While it has a higher resistivity than copper wire, it's still negligible. It adheres really well too. The normal heat from operation of the CRT isn't going to hurt it either.

Young people tend to be better optimists. Less experience at failing I suppose. :D