Help with a 12LP4! - Videokarma.org TV - Video

benman94 · #1 06-13-2011, 12:39 PM

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?

Thanks,
Benny

jeyurkon · #2 06-13-2011, 12:57 PM

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

Quote:

Originally Posted by benman94

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?

Thanks,
Benny

Mal Fuller · #3 06-13-2011, 01:26 PM

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.

pearsonk · #4 06-13-2011, 02:22 PM

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

Steve McVoy · #5 06-13-2011, 04:06 PM

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.

charokeeroad · #6 06-13-2011, 06:15 PM

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

MelodyMaster · #7 06-13-2011, 06:58 PM

Quote:

Originally Posted by charokeeroad

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?

VintagePC · #8 06-13-2011, 07:09 PM

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.

Phil Nelson · #9 06-13-2011, 08:35 PM

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

6GH8cowboy · #10 06-13-2011, 08:56 PM

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.

MelodyMaster · #11 06-13-2011, 09:55 PM

Quote:

Originally Posted by VintagePC

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.

VintagePC · #12 06-14-2011, 07:27 AM

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

benman94 · #13 06-14-2011, 05:00 PM

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

VintagePC · #14 06-14-2011, 05:52 PM

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

benman94 · #15 06-24-2011, 04:56 PM

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 . . .)?