12LP4 base ripped off, questions about putting back together.

[DeLorean00]

Hello, I am new here. I am working on an old Andrea Radio CVK12 TV console with 12LP4 tube that the base got ripped off when it was being moved before I got the tv. I have another 12LP4 so I can replace it but I wanted to try and fix this one first because this was supposedly a working unit a couple of years ago.

So the question I have is there are 5 wires left, is that correct? I see others are snipped off at the base of the tube. The other question is how do the wires route? See the attached picture, I am unsure how to figure which wire goes to which pin.

I have never run into this situation so I figured I would ask the experts over here before I make a mistake.

Thanks in advance!

[dtvmcdonald]

You determine the orientation by two methods:

1) use an ohmmeter and find which two wires are the heater

2)determine what the orientation of the key is by examining the
datasheet (google "12LP4 pocnet") to see the pattern of unused pins.

These should agree.

To fix the tube, go to your Lowe's etc. and get a round diamond grit disk cutter tool
for a Dremel tool. You don't need the Dreml tool ... you work by hand.
Then slowly use the tool to grind down the glass, very carefully, around each lead broken exactly at the glass, 1/32 inch will do. It the lead sticks out even a little that's
not necessary.

Then solder on a 3 inch length of one conductor from piece of stranded hookup wire
to each nub. These can be threaded through the cleaned out base pins, along with the
unbroken wires. Then solder the wires to the pins.

Of course you have to attach the base to the tube. I've always used duct tape ...
this is politically incorrect.

[DeLorean00]

Originally Posted by dtvmcdonald

You determine the orientation by two methods:

1) use an ohmmeter and find which two wires are the heater

2)determine what the orientation of the key is by examining the
datasheet (google "12LP4 pocnet") to see the pattern of unused pins.

These should agree.

To fix the tube, go to your Lowe's etc. and get a round diamond grit disk cutter tool
for a Dremel tool. You don't need the Dreml tool ... you work by hand.
Then slowly use the tool to grind down the glass, very carefully, around each lead broken exactly at the glass, 1/32 inch will do. It the lead sticks out even a little that's
not necessary.

Then solder on a 3 inch length of one conductor from piece of stranded hookup wire
to each nub. These can be threaded through the cleaned out base pins, along with the
unbroken wires. Then solder the wires to the pins.

Of course you have to attach the base to the tube. I've always used duct tape ...
this is politically incorrect.

Thank you for your reply. So I have 5 wires still coming from the tube in full length, and the tube socket does have 7 pins but it appears two are not used.

If I am understanding the tube data 12LP4 pocnet, I should have 2 pins for the heater, 2 for the grid, and 1 for the cathode.

So if I figure out which 2 are the heater, I should be able to use them to figure the location of the others.

[WISCOJIM]

No need for all that work. The five wires are side by side and align with the five consecutive pins on the base.

.

[DeLorean00]

Originally Posted by WISCOJIM

No need for all that work. The five wires are side by side and align with the five consecutive pins on the base.

.

Thanks! I did have the meter out and verified that heater was right where should it be if all 5 were side by side. I was only a little confused at first as some are cut and wasn't sure how to clock the base.

I ordered some electronics grade RTV to reattach the base and will just solder the leads back in place.

I appreciate all the help!

[Electronic M]

Couple of tips: Heat and desolder the leads and pins (file or poke the ends of the pins with a screwdriver to open them more after if needed) so you can see the lead in the hole before you install the base. If any lead is on the short side and difficult to get in the pin a single 3" strand from stranded lamp cord or a single solid core phono tonearm lead (Radio Shack used to sell good stuff) added to the end of the original helps to thread it right.

[Eric H]

If you need to bend the wires to align them don't let it bend at the glass, it will break off.

[DeLorean00]

Originally Posted by Electronic M

Couple of tips: Heat and desolder the leads and pins (file or poke the ends of the pins with a screwdriver to open them more after if needed) so you can see the lead in the hole before you install the base. If any lead is on the short side and difficult to get in the pin a single 3" strand from stranded lamp cord or a single solid core phono tonearm lead (Radio Shack used to sell good stuff) added to the end of the original helps to thread it right.

Thank you for the tips! I really appreciate it!

Originally Posted by Eric H

If you need to bend the wires to align them don't let it bend at the glass, it will break off.

Ah, yeah that is a great point I didn't consider. I will carefully bend the wires above the glass just enough to get proper routing and no shorts. Thanks!

I'm really curious to see what this CRT shows when I hook it up to my Super Mack when I am done. Even if it is super weak, I will still have learned a lot.

[DeLorean00]

So I am having some issues getting this base back on. I bent all the leads into roughly the correct shape but it is really hard to get them to fit into the base because the sides come down and make it basically a blind job. After tons of attempts, I seem to always get one wire not seated, then I finally got all 5 in I think but I really wasn't able to verify. The wires did not come exactly flush to the edge of the pins on 3 of them. I tried flooding all with solder but I still had a bad connection with one pin because emission was zero unless I slightly touched the base. So I ended up pulling the base off again starting over.

So what I have tried is soldering on some solid core wire the same gauge to extend the wires out enough to get more working room. However, the problem I am having with that is when I try to get the soldered joint inside the pin it won't fit, even though they are butt to butt and soldered with the only the smallest amount of solder possible.

I have considered removing the extending wires, then cutting part of one side of the tube base cap off so I can use it to align and adjust the pins. Given this will make it weaker when its glued in place, but I am running out of ideas on how I should make this work.

The final thing I have heard Bob Andersen talk about is a pin crimper, that might help me on the leads that are a little short. Has anyone used one of those before? I have a ratching crimping tool with adjustable heads I use for Molex connectors that might work.

Chris

[ohohyodafarted]

I have done this several times. I found that just cleaning the pins out is not good enough. After I remove all the solder by heating with an iron and slamming down on the work bench to get most of the solder out of the pins, I then take a small drill bit ( sorry I can remember what size, but is either a #60 or possibly slightly larger) and drill out the pins to get the inside perfectly clean right down to the inside walls of the brass pins.

With the inside of the pins perfectly clean it is much easier to get the wires to slide inside the pins. Sometimes I will extend the wires like you did, but usually if the original wires are clean you can get them lined up perfectly and they should slide into the pins after a little bit of trial and error.

[DeLorean00]

Originally Posted by ohohyodafarted

I have done this several times. I found that just cleaning the pins out is not good enough. After I remove all the solder by heating with an iron and slamming down on the work bench to get most of the solder out of the pins, I then take a small drill bit ( sorry I can remember what size, but is either a #60 or possibly slightly larger) and drill out the pins to get the inside perfectly clean right down to the inside walls of the brass pins.

With the inside of the pins perfectly clean it is much easier to get the wires to slide inside the pins. Sometimes I will extend the wires like you did, but usually if the original wires are clean you can get them lined up perfectly and they should slide into the pins after a little bit of trial and error.

Thanks for the tip! I will try drilling it out.

[MadMan]

I would also tin the leads before putting the base back on, if they aren't already.

[AlanInSitges]

I saw a video of Bob Andersen's where he solders some fine wire onto the ends of those leads long enough to feed them easily into the pins. That seems to make it a much easier process.

[DeLorean00]

Originally Posted by MadMan

I would also tin the leads before putting the base back on, if they aren't already.

You know that makes so much sense, I wish I had done that the one time I had all the pins in. I probably could have just heated them and flooded the tip with solder and been good. Thanks for pointing that out. I really appreciate it.

Originally Posted by AlanInSitges

I saw a video of Bob Andersen's where he solders some fine wire onto the ends of those leads long enough to feed them easily into the pins. That seems to make it a much easier process.

You are right. Last night I found an old video from Bob Andersen where he goes into great detail with two different tubes about how to reattach the base. One he fed the wires through the base and then attached them to wires on the CRT by J hooks. In that situation, I would have to trim my wires down a bit. But his method of inserting the wires into the base and then attaching them to the CRT makes so much sense. I have learned so much from watching Bob, I am really glad he takes the time to make videos.

He also had a second method where he butt matched wires than he cut them into descending lengths starting with a really long one around 4" and ending with one around 1 1/2", that way he can just insert one wire at a time into the base. This is a method I had just about stumbled upon myself in trying to come up with a solution.

For anyone interested here is Bob Andersen's video on this.
https://www.youtube.com/watch?v=LQQLTnaYU9U