Videokarma.org

Go Back   Videokarma.org TV - Video - Vintage Television & Radio Forums > Early Color Television

We appreciate your help

in keeping this site going.
Reply
 
Thread Tools Display Modes
  #1  
Old 12-20-2018, 04:55 PM
Skywaffle Skywaffle is offline
VideoKarma Member
 
Join Date: Sep 2017
Posts: 3
Questions regarding broken CRT lead

Hello,
I have been working on an RCA CTC-20C which started with a mostly dead CRT (among other issues). After some time on the rejuvenator, the CRT was able to produce a fairly good picture overall. This became short lived when I decided to work on the chassis some and afterwards would not get any neck glow. Upon de-soldering the bakelite base, I noticed that one of the leads had broken off mostly flush (somewhat recessed) to the glass.

Has anyone encountered this type of issue before? If so, has anyone found a way to repair this type of damage?

Thanks,
Matthew
Reply With Quote
  #2  
Old 12-20-2018, 05:41 PM
Electronic M's Avatar
Electronic M Electronic M is offline
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 10,405
If it is recessed things get difficult.

I'm guessing you lost a heater lead. If it was not a heater lead you could probably use conductive glue, but the heater draws a lot of current and odds are conductive glue won't survive that...

If the glass is reasonably thick around the lead and there's a raised bit of glass wrapped around the lead stub then you may be able to expose a solder able nub by grinding the glass down with a small gentle dremmel grinding bit.... but grind too far and you loose vacuum. Also you have to apply heat with the soldering iron for the shortest possible time needed to get a solder joint....too long heating it and the glass will crack and the vacuum will leak... grinding the glass will also make it more prone to cracking.......

What you have is a game of finesse, speed, judgement and luck with the future of your CRT on the line....No pressure.
__________________
Tom C.

What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4

Reading between the scan lines since the mid 2000's.
Reply With Quote
  #3  
Old 12-20-2018, 06:49 PM
Skywaffle Skywaffle is offline
VideoKarma Member
 
Join Date: Sep 2017
Posts: 3
What a heartbreaking experience. I will try to clean up the area and see if I can expose any of the wire. It appears that there is a bit of oxidation at the base of all the leads.. But only the one managed to break (or maybe burned up; the glass stub you speak of that can be ground down is chipped.)

Going into the project, I initially never had much hope with the initial condition of the CRT. But things were really looking positive after the rejuvenation. It was a joy to watch for the brief time I could.
Reply With Quote
  #4  
Old 12-20-2018, 07:53 PM
Jeffhs's Avatar
Jeffhs Jeffhs is offline
<----Zenith C845
 
Join Date: Feb 2003
Location: Fairport Harbor, Ohio (near Lake Erie)
Posts: 3,581
Quote:
Originally Posted by Skywaffle View Post
What a heartbreaking experience. I will try to clean up the area and see if I can expose any of the wire. It appears that there is a bit of oxidation at the base of all the leads.. But only the one managed to break (or maybe burned up; the glass stub you speak of that can be ground down is chipped.)

Going into the project, I initially never had much hope with the initial condition of the CRT. But things were really looking positive after the rejuvenation. It was a joy to watch for the brief time I could.
I agree with Electronic M's assessment of your situation. I hate to say this, but unless you can find some way to expose enough of the broken lead to solder to it (not likely, given how short it is), and the very real possibility of ruining the tube if anything goes wrong while you are working on it, your CRT is junk and must be replaced. I would try to find a good used CRT from a junked set. In this age of flat-screen TVs, it may not be easy to find a replacement for any size CRT, as these tubes are becoming very scarce and are all but impossible to find new--needless to say, no one makes CRTs anymore. I am not familiar with the CTC20 chassis, so I don't know if it uses a round or a rectangular CRT.

Further, if you rejuvenated the tube with a CRT tester, bear in mind that any improvement you may notice won't last long, so it is probably just as well that you will have to replace the tube. Rejuvenation is usually done only to restore a CRT to usable condition (albeit dim) until the tube can be replaced; it is not meant to be a permanent fix. The tube will eventually dim again, at which point it must be replaced. CRT brighteners were often used in the 1950s-'60s to extend the usable life of dimming tubes, but again, this was only a stopgap measure and usually resulted in a dim CRT again within months; the only solution in this case was either to replace the tube or the TV.
__________________
Jeff, WB8NHV

Collecting, restoring and enjoying vintage Zenith radios since 2002

Zenith. Gone, but not forgotten.

Last edited by Jeffhs; 12-20-2018 at 08:13 PM.
Reply With Quote
  #5  
Old 12-20-2018, 10:35 PM
Crist Rigott Crist Rigott is offline
VideoKarma Member
 
Join Date: Oct 2015
Location: Waxahachie, TX
Posts: 1,310
See reply #218.
http://www.videokarma.org/showthread...master&page=15
Reply With Quote
Audiokarma
  #6  
Old 12-21-2018, 11:14 AM
Skywaffle Skywaffle is offline
VideoKarma Member
 
Join Date: Sep 2017
Posts: 3
This tube is a round 21fjp22. The TV had a brightener on it when I had acquired it, but would not produce much of any kind of image initially. On the tester none of the guns would show any readings until the rejuvenation was performed. The difference afterwards resulted in a picture that was very impressive in a lit room (compared to an extremely dark unfocused looking picture in a dark room). I suppose I had hoped maybe this would be a fairly long term fix.

Quote:
Originally Posted by Jeffhs View Post
I agree with Electronic M's assessment of your situation. I hate to say this, but unless you can find some way to expose enough of the broken lead to solder to it (not likely, given how short it is), and the very real possibility of ruining the tube if anything goes wrong while you are working on it, your CRT is junk and must be replaced. I would try to find a good used CRT from a junked set. In this age of flat-screen TVs, it may not be easy to find a replacement for any size CRT, as these tubes are becoming very scarce and are all but impossible to find new--needless to say, no one makes CRTs anymore. I am not familiar with the CTC20 chassis, so I don't know if it uses a round or a rectangular CRT.

Further, if you rejuvenated the tube with a CRT tester, bear in mind that any improvement you may notice won't last long, so it is probably just as well that you will have to replace the tube. Rejuvenation is usually done only to restore a CRT to usable condition (albeit dim) until the tube can be replaced; it is not meant to be a permanent fix. The tube will eventually dim again, at which point it must be replaced. CRT brighteners were often used in the 1950s-'60s to extend the usable life of dimming tubes, but again, this was only a stopgap measure and usually resulted in a dim CRT again within months; the only solution in this case was either to replace the tube or the TV.
Reply With Quote
  #7  
Old 12-21-2018, 11:46 AM
dtvmcdonald's Avatar
dtvmcdonald dtvmcdonald is offline
VideoKarma Member
 
Join Date: Nov 2012
Posts: 861
If it is not the heater conductive glue will work fine.

If you are afraid of overheating to solder, get some pure Indium wire off
ebay and use that as solder, using ordinary liquid flux. It melts at just the
right temperature, solders easy and won't melt with ordinary base heat. Indium
can't hurt ... its a good solder and sticks well to copper, steel, other tube pin
alloys, and ordinary solder. I've even had good luck soldering to germanium with it!

Use a small wire and glue down to the glass after soldering.

But ... I've had good luck with regular solder and a tiny tip on both CRTs and
a very rare iconoscope.
Reply With Quote
  #8  
Old 12-21-2018, 12:20 PM
Electronic M's Avatar
Electronic M Electronic M is offline
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 10,405
Quote:
Originally Posted by Skywaffle View Post
This tube is a round 21fjp22. The TV had a brightener on it when I had acquired it, but would not produce much of any kind of image initially. On the tester none of the guns would show any readings until the rejuvenation was performed. The difference afterwards resulted in a picture that was very impressive in a lit room (compared to an extremely dark unfocused looking picture in a dark room). I suppose I had hoped maybe this would be a fairly long term fix.
BTW if a CRT has not been used for a few years the cathode will act as a getter and that will coat the emissive surface in crud that blocks emission....we call it the CRT falling asleep. When a CRT is asleep a rejuve is a dangerous way to wake it up (you can burn off the emissive surface along with the crud covering it). The best way to wake up a CRT is to let it sit on the tester in emission mode for as much as an hour ( check for improvement every 15 min) if it doesn't Improve or barely improves increase the.heater voltage to 1.4x it's designed value and repeat the process, THEN if there's still no life or much less than a usable value you can try a rejuve.

Rejuvination is risky use all safer measures first.
__________________
Tom C.

What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4

Reading between the scan lines since the mid 2000's.
Reply With Quote
  #9  
Old 12-21-2018, 01:21 PM
old_coot88 old_coot88 is offline
VideoKarma Member
 
Join Date: Sep 2009
Posts: 1,959
Quote:
Originally Posted by Electronic M View Post

Rejuvination is risky use all safer measures first.

Agree 110%. Rejuv only after all other measures (including CRT brightener) have failed. Learn't that the hard way many moons ago.
Reply With Quote
  #10  
Old 12-22-2018, 01:12 PM
andy's Avatar
andy andy is offline
VideoKarma Member
 
Join Date: Jul 2002
Location: Austin, TX
Posts: 4,004
I've made similar repairs in the past by filing away a small amount of glass around the broken wire. Then apply a small piece of copper foil tape over the stub so it pierces the tape and solder it. The tape gives you a large surface area to solder to, and provides some mechanical support for the connection. You can even reinforce it with epoxy if you want to. Finally, solder some thin wire to the tape (I would use wire wrap wire).
Reply With Quote
Audiokarma
  #11  
Old 12-22-2018, 01:29 PM
Phil Nelson's Avatar
Phil Nelson Phil Nelson is offline
VideoKarma Member
 
Join Date: Jan 2006
Posts: 3,966
I have used silver-filled (i.e., conductive) epoxy to repair a similar problem on a CRT base:

https://antiqueradio.org/CapehartFar...airingTubeBase

Phil Nelson
Phil's Old Radios
https://antiqueradio.org/index.html
Reply With Quote
  #12  
Old 12-22-2018, 02:17 PM
jr_tech's Avatar
jr_tech jr_tech is offline
VideoKarma Member
 
Join Date: Sep 2009
Posts: 3,876
But is silver epoxy conductive enough to repair a lead that carries heater current in a 3 gun color CRT (1.8 amps nominal, and much more at cold turn on) ?

jr
Reply With Quote
  #13  
Old 12-22-2018, 03:38 PM
Phil Nelson's Avatar
Phil Nelson Phil Nelson is offline
VideoKarma Member
 
Join Date: Jan 2006
Posts: 3,966
Don’t know offhand, but this page has some specs:

https://www.mgchemicals.com/products...ive-epoxy-8331

Phil Nelson
Reply With Quote
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 11:18 PM.



Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
©Copyright 2012 VideoKarma.org, All rights reserved.