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
  #16  
Old 03-15-2011, 12:06 PM
kx250rider's Avatar
kx250rider kx250rider is offline
REAL TVs have TUBES!
 
Join Date: Oct 2005
Location: Los Angeles & Dallas
Posts: 3,238
I agree with Steve K... His experience on the early color sets is about as strong as you can get in 2011. Further, I agree that Sams is probably NOT what I'd use. I have (same as Steve) the RCA factory manuals and supplements. I doubt that your TV has any non-factory authorized changes in it; especially if it's been in your hands since '70x. If it had passed through the hands of other TV collectors, maybe I'd worry there had been switchy-changey of things. I had a 21CT55 that had been heavily modified to accept composite input, and was changed to a glass tube, and had been retrofitted with a solid-state B+ regulator. Needless to say, that became a "parts set".

Charles
__________________
Collecting & restoring TVs in Los Angeles since age 10
Reply With Quote
  #17  
Old 03-15-2011, 12:46 PM
Sandy G's Avatar
Sandy G Sandy G is offline
Spiteful Old Cuss
 
Join Date: May 2003
Location: Rogersville, Tennessee
Posts: 9,077
You lucky Dawg...That is a VERY desirable set ! Can't wait to see "Working" pics of it & its "Glorious Lollipop Color"...(grin)
__________________
Benevolent Despot
Reply With Quote
  #18  
Old 03-15-2011, 05:58 PM
Findm-Keepm's Avatar
Findm-Keepm Findm-Keepm is offline
Followin' the Rules...
 
Join Date: Jun 2007
Posts: 2,826
Calvert or St Mary's? I'd love to see a 21CT55 live, in operation!

Cheers,
__________________
Brian
USN RET (Avionics / Cal)
CET- Consumer Repair and Avionics ('88)
"Capacitor Cosmetologist since '79"

When fuses go to work, they quit!
Reply With Quote
  #19  
Old 03-15-2011, 06:09 PM
stromberg6's Avatar
stromberg6 stromberg6 is offline
VideoKarma Member
 
Join Date: Sep 2004
Location: Ellington,CT
Posts: 465
When I did my 4 & 5N, I used Sams, RCA service publications, and also noted every step of the way just what each circuit looked like as wired, and had no problems at all other than what one would expect in a restoration. Low hours set, the 4, with all factory mods. One thing I did do in the 4 was put the chroma amp circuit back to original. I believe it was wired to bypass the automatic color control circuit to allow more gain. I like it the way the engineers designed it, but to each his own.
Kevin
__________________
stromberg6
Reply With Quote
  #20  
Old 03-15-2011, 07:45 PM
Zenith6S321's Avatar
Zenith6S321 Zenith6S321 is offline
VideoKarma Member
 
Join Date: Aug 2010
Location: Piney Point, Maryland
Posts: 303
Steve McVoy, PM sent.

Phil, I have no illusions that I can solve such a challenging problem, but its sure fun to investigate. Back in the 70's I used my old Knight Kit emissions tester, EICO low frequency O-scope, and EICO VTVM to fix all my neighbors B&W tvs and did manage to get the 21CT55 working. Everyone that saw it found the picture quality amazing compared to the 70's vintage picture quality. I never was able to get very good convergence at the edges of the screen. I think I recall that the HOT coupling capacitor was leaky, which may have caused the first flyback to give out? I did have to replace the 30KV HV cap, as it was shorted. The 21AXP22A had been replaced with the 21AXP22A. A 21AXP22/21AXP22A data sheet PDF says "The 21AXP22A features an internal neck coating having high resistance which eliminates the need for an external resistor between the anode power supply and the tube to proctect against damage by a momentary arc." But the CTC2B Ultor lead includes a resistor between the CRT and the HV section. Is it possible that the internal CRT resistor reduced the current draw and allowed the HV to exceed the 30KV cap rating? I did have problems with arcs from the exposed HV part. I now doubt the accuracy of my old VTVM and HV probe back then.
Reply With Quote
Audiokarma
  #21  
Old 03-15-2011, 08:00 PM
Zenith6S321's Avatar
Zenith6S321 Zenith6S321 is offline
VideoKarma Member
 
Join Date: Aug 2010
Location: Piney Point, Maryland
Posts: 303
KX250, my set had a replacement 21AXP22A CRT and flyback in it when I got it, but it had not been in operation after the flyback went in. Plus it needed some electrolytics before I got it working again, way back then. Steve is sending me the RCA info for the set, so I'm going to use that for reference (especially in the flyback/convergence/HV section) while the rest I will keep wired as is, but with new parts where needed.

Sandy, I agree as witnessed by a, then, college kid spending $75 in the 70's to buy an old broken TV.


Findm, I'm way down south in St. Mary's county. I will post picturess when I have something "photogenic".

Stromberg, I'll keep an eye out in that area of mine then, thanks.
Reply With Quote
  #22  
Old 03-15-2011, 09:00 PM
old_tv_nut's Avatar
old_tv_nut old_tv_nut is offline
See yourself on Color TV!
 
Join Date: Jul 2004
Location: Rancho Sahuarita
Posts: 4,724
Quote:
Originally Posted by Zenith6S321 View Post
Steve McVoy, PM sent.
Is it possible that the internal CRT resistor reduced the current draw and allowed the HV to exceed the 30KV cap rating?
I don't think so, since the current load from the CRT normally goes to zero on a black screen, and the regulator takes it all.

A shunt regulator works by measuring the current at the bottom of the flyback and keeping the total constant. Total current is divided between the CRT and the regulator, depending on how much the CRT demands. If the regulator fails, you could get an overvoltage, but not if it's working normally.
Reply With Quote
  #23  
Old 03-15-2011, 09:45 PM
reeferman's Avatar
reeferman reeferman is offline
VideoKarma Member
 
Join Date: Jun 2004
Location: St. Louis
Posts: 511
Zen,
I can send a copy the RCA color tv field service guide should you want it.
Phil
Reply With Quote
  #24  
Old 03-15-2011, 09:54 PM
miniman82's Avatar
miniman82 miniman82 is offline
First Light: 1952-2011
 
Join Date: Jun 2009
Location: Great Mills, MD
Posts: 4,118
That's right, Wayne. IMO if the HV cap failed, it was probably due to internal breakdown and arcing all on it's own, but that's also likely what took out the flyback. Looking at the schematics, it appears RCA might have realized their mistake. On the CTC-4, the HV tower incorporates it's own set of resistors between the output of the HV rectifier and the shunt reg/CRT. This way even if the shunt or CRT shorts, the resistors end up sinking all the current so presumably the flyback could live. Same principle as the resistor used on sets that used the 21CYP22 CRT- shorting protection. It's probably possible to mod the 21CT55 to include this type of protection; it would not be original so purists might object, but it's cheap insurance against a failure that would destroy an irreplaceable flyback transformer. Just my 2 cents.
__________________
Evolution...
Reply With Quote
  #25  
Old 03-16-2011, 08:21 PM
Zenith6S321's Avatar
Zenith6S321 Zenith6S321 is offline
VideoKarma Member
 
Join Date: Aug 2010
Location: Piney Point, Maryland
Posts: 303
Yeah, I see what you mean in the CTC4 HV schematics. I will add moving that resistor before the regulator to my todo list. Thanks.
Reply With Quote
Audiokarma
  #26  
Old 03-18-2011, 11:06 PM
Zenith6S321's Avatar
Zenith6S321 Zenith6S321 is offline
VideoKarma Member
 
Join Date: Aug 2010
Location: Piney Point, Maryland
Posts: 303
The 21CT55 RCA information that Steve K sent arrived today. Its much more detailed than the Sams And my convergence chassis wiring matches the RCA schematic, which the Sams did not. Thanks again Steve K for the information!!! Now to start recapping and checking all resistance values, cleaning contacts, cleaning 50+ years of dust, etc.... And then theres the cabinet, which I guess I will save for after the electronics are finished.
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 06:35 PM.



Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
ęCopyright 2012 VideoKarma.org, All rights reserved.