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
  #166  
Old 03-23-2017, 09:59 PM
dieseljeep dieseljeep is offline
VideoKarma Member
 
Join Date: Jul 2010
Posts: 5,784
Quote:
Originally Posted by Electronic M View Post
I've made it into one.
I picked up a Radio Shack bulk tape eraser, that works great! It's a black plastic unit, that looks like a travel iron. It's a real powerful item, that can be used to demagnitize, just about any kind of magnetic media. It also works well as a deguasser, even though, I still have the first RCA DG coil, I bought over 50 years ago.
Reply With Quote
  #167  
Old 03-24-2017, 08:09 AM
kvflyer kvflyer is offline
VideoKarma Member
 
Join Date: Nov 2006
Location: Catonsville, MD, USA
Posts: 801
I too use a Radio Shack bulk eraser. It is very powerful and does the job.
Reply With Quote
  #168  
Old 03-25-2017, 04:15 PM
SwizzyMan's Avatar
SwizzyMan SwizzyMan is offline
Restoring an admiral c322
 
Join Date: Apr 2015
Location: Orlando FL
Posts: 845
Put in the new crystal and things have improved I believe. The oscillator isnt running at the correct frequency as indicated by the lack of color sync. I dont see nearly as much interference anymore. I did blow out the hv cage with compressed air and moved 1 lead that was somewhat close to a solder joint. I'm not sure if I should adjust L127. Fine tuning isnt able to lock the color and neither is the color control. I think I may have to adjust L127 (reactance coil). Still have no red.
Attached Images
File Type: jpg 20170325_155654.jpg (67.5 KB, 42 views)
__________________

Admiral C322C2 Regent (Restoring)
RCA CTC-7 Pensbury (Restored)
RCA CTC-5 Westcott (Restored)
CRA CTC--4 Director 21 (Restoring)
Reply With Quote
  #169  
Old 03-25-2017, 05:36 PM
SwizzyMan's Avatar
SwizzyMan SwizzyMan is offline
Restoring an admiral c322
 
Join Date: Apr 2015
Location: Orlando FL
Posts: 845
14 turns counter-clockwise on L127 made the rolling bars a lot higher, but I still cant get it to lock. I reverted L127 back to its original position. I need to hook up the frequency counter and see what the oscillator is running at.
__________________

Admiral C322C2 Regent (Restoring)
RCA CTC-7 Pensbury (Restored)
RCA CTC-5 Westcott (Restored)
CRA CTC--4 Director 21 (Restoring)

Last edited by SwizzyMan; 03-25-2017 at 05:53 PM.
Reply With Quote
  #170  
Old 03-25-2017, 06:28 PM
SwizzyMan's Avatar
SwizzyMan SwizzyMan is offline
Restoring an admiral c322
 
Join Date: Apr 2015
Location: Orlando FL
Posts: 845
I connected the frequency counter to the oscillator. It measured out at about 3.58MHz which was good. The target frequency is 3.57545 so I went off of that. The lowest I could get the oscillator by turning L127 (reactance coil) was 3.57970 which was plenty off. I think I need to add a cap in parallel with the 270 pf cap on the oscillator tank circuit. Your thoughts?
Attached Images
File Type: jpg 20170325_180253.jpg (59.2 KB, 21 views)
File Type: jpg 20170325_180625.jpg (65.0 KB, 19 views)
__________________

Admiral C322C2 Regent (Restoring)
RCA CTC-7 Pensbury (Restored)
RCA CTC-5 Westcott (Restored)
CRA CTC--4 Director 21 (Restoring)
Reply With Quote
Audiokarma
  #171  
Old 03-25-2017, 08:03 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: 4,319
Do you know if the capacitors are OK
C201 2p
C202 120p
C209 6.8p
C203 .01
C213 270

How about the reactance tube itself (6AN8)?

The reactance tube works by amplifying the effect of C201 by the variable gain of the tube.

You can check if the oscillator can be pulled by putting, I don't know for sure, but maybe 100pF, from the plate of the reactance tube to ground. If this can pull the oscillator to a lower frequency, and the reactance tube cannot, the problem is in the reactance tube circuit.
__________________
www.bretl.com
Old TV literature, New York World's Fair, and other miscellany
Reply With Quote
  #172  
Old 03-25-2017, 09:16 PM
SwizzyMan's Avatar
SwizzyMan SwizzyMan is offline
Restoring an admiral c322
 
Join Date: Apr 2015
Location: Orlando FL
Posts: 845
Quote:
Originally Posted by old_tv_nut View Post
Do you know if the capacitors are OK
C201 2p
C202 120p
C209 6.8p
C203 .01
C213 270

How about the reactance tube itself (6AN8)?

The reactance tube works by amplifying the effect of C201 by the variable gain of the tube.

You can check if the oscillator can be pulled by putting, I don't know for sure, but maybe 100pF, from the plate of the reactance tube to ground. If this can pull the oscillator to a lower frequency, and the reactance tube cannot, the problem is in the reactance tube circuit.
I will check the tube first. This is somewhat confusing though because the previous crystal was able to oscillate at the right frequency and maintain color lock until the crystal broke. And after doing some reading around it seems Phil Nelson had this same problem with his 4 and adding a cap in parallel with the tank circuit allowed the correct frequency to be reached.
__________________

Admiral C322C2 Regent (Restoring)
RCA CTC-7 Pensbury (Restored)
RCA CTC-5 Westcott (Restored)
CRA CTC--4 Director 21 (Restoring)
Reply With Quote
  #173  
Old 03-25-2017, 11:55 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: 4,319
Quote:
Originally Posted by SwizzyMan View Post
I will check the tube first. This is somewhat confusing though because the previous crystal was able to oscillate at the right frequency and maintain color lock until the crystal broke. And after doing some reading around it seems Phil Nelson had this same problem with his 4 and adding a cap in parallel with the tank circuit allowed the correct frequency to be reached.
I think you are right to try the tube first. If that's not the problem:

A crystal for this circuit is cut to parallel resonate with a certain net amount of capacitance. That is, the crystal is operated above its series resonant frequency, and behaves like a large inductor, and is tuned with a small parallel capacitance. If the tank coil is tuned right on frequency, the net capacitance is supplied by the reactance circuit through the 120 pf C202.
The tank being on the far side of the 6.8 pF, it takes a large change in the tank tuning to change the total parallel capacitance across the crystal. I don't doubt that it worked, but a more direct way might be to put a small cap (5-10 pF) directly across the crystal. This way, the tank doesn't have to be detuned so far to get the required net capacitance. Adding capacitance across the tank means you are detuning it from exact parallel resonance to be capacitive when the oscillator is locked, while I think it is really intended to be more or less exactly parallel resonant for oscillator operation.

Different TV manufacturers may have specified different parallel capacitances, for nominal parallel resonance of the crystal. (probably between 18 pF for Zenith [if i recall correctly] and possibly higher values [maybe up to 32 pf but probably in the 20s] for other manufacturers). So, it's possible the crystal you got is not cut for the net capacitance in this chassis, and some more capacitance is needed. This should come from the reactance circuit, not the tank circuit, which is why you tune the reactance coil to zero beat the oscillator.
__________________
www.bretl.com
Old TV literature, New York World's Fair, and other miscellany
Reply With Quote
  #174  
Old 04-01-2017, 05:50 PM
SwizzyMan's Avatar
SwizzyMan SwizzyMan is offline
Restoring an admiral c322
 
Join Date: Apr 2015
Location: Orlando FL
Posts: 845
I tacked on a 5 pf cap across the crystal and I can almost get the oscillator to run at the right frequency. It still wont lock even after 20 turns on the reactance coil. Here is what I could get (note the bars rapidly change color every second but I no longer have the barber pole rainbow.)
Attached Images
File Type: jpg 20170401_171328.jpg (89.5 KB, 53 views)
__________________

Admiral C322C2 Regent (Restoring)
RCA CTC-7 Pensbury (Restored)
RCA CTC-5 Westcott (Restored)
CRA CTC--4 Director 21 (Restoring)
Reply With Quote
  #175  
Old 04-01-2017, 07:59 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: 4,319
Ok, now you have a chance to find out what part of the loop is dead.

If you have a scope, connect to the top of C198 (4700). If you don't have a scope, connect a DC voltmeter there. Center the AFC balance control. Tune the oscillator so the color cycles through slowly, and you should see the voltage cycle slowly also, as the phase detector cycles through its full range. I don't know what the normal range is, but it should be at least a few volts variation, maybe +/- 10 from nominal zero at most? [Note that the schematic says the nominal control voltage on the grid of the reactance tube is zero volts, so the phase detector output should vary +/- around zero when it is out of lock.] If there is no variation, then either the burst keyer or the phase detector may be dead. If there is a variation, then your problem is still in the reactance tube or oscillator.
__________________
www.bretl.com
Old TV literature, New York World's Fair, and other miscellany

Last edited by old_tv_nut; 04-01-2017 at 08:04 PM.
Reply With Quote
Audiokarma
  #176  
Old 04-03-2017, 05:03 PM
SwizzyMan's Avatar
SwizzyMan SwizzyMan is offline
Restoring an admiral c322
 
Join Date: Apr 2015
Location: Orlando FL
Posts: 845
I checked voltages and waveforms at C198 which is a .01 in this case since I have the early production run of the chassis. I got about 10 volts on the top side of the .01 and 0 volts at the ground side. I didnt see any variation in voltage when adjusting the reactance coil (provided I adjusted the right coil). Here is the waveform I observed at the top side of this cap. Please note that all these measurements were taken with the chassis on the workbench. So no HV or connection to the CRT at all. Here is what I found.
Attached Images
File Type: jpg 20170403_163624.jpg (47.6 KB, 11 views)
File Type: jpg 20170403_164009.jpg (62.8 KB, 9 views)
File Type: jpg 20170403_164015.jpg (62.3 KB, 4 views)
__________________

Admiral C322C2 Regent (Restoring)
RCA CTC-7 Pensbury (Restored)
RCA CTC-5 Westcott (Restored)
CRA CTC--4 Director 21 (Restoring)
Reply With Quote
  #177  
Old 04-03-2017, 06:59 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: 4,319
Forget the HV, but is the horizontal running on the workbench? It has to be running in order to get a burst gate pulse. No burst gate, nothing gets to the phase detector, so impossible to tell what's wrong or not.

Also, is the scope set for DC coupling? The variation you are looking for is slow, same rate as the color changing a few times per second, so with your high speed scope setting and DC coupling, you would expect the trace to go up and down a few times a second, in sync with the color phase changing. If the scope is set to AC coupling, you won't see such a slow variation at all.

One more thing - if the color is changing rapidly, the voltmeter may not respond in time, that's why the scope is preferred.
__________________
www.bretl.com
Old TV literature, New York World's Fair, and other miscellany

Last edited by old_tv_nut; 04-03-2017 at 07:04 PM.
Reply With Quote
  #178  
Old 04-03-2017, 07:26 PM
SwizzyMan's Avatar
SwizzyMan SwizzyMan is offline
Restoring an admiral c322
 
Join Date: Apr 2015
Location: Orlando FL
Posts: 845
Quote:
Originally Posted by old_tv_nut View Post
Forget the HV, but is the horizontal running on the workbench? It has to be running in order to get a burst gate pulse. No burst gate, nothing gets to the phase detector, so impossible to tell what's wrong or not.

Also, is the scope set for DC coupling? The variation you are looking for is slow, same rate as the color changing a few times per second, so with your high speed scope setting and DC coupling, you would expect the trace to go up and down a few times a second, in sync with the color phase changing. If the scope is set to AC coupling, you won't see such a slow variation at all.

One more thing - if the color is changing rapidly, the voltmeter may not respond in time, that's why the scope is preferred.
Oh duh...horizontal was not running. I will need to make a shorting bar for the yoke socket to get it to turn on. Back to square one. Scope was set on ac. When set on DC the trace disappears (please bear with me im new to scopes).
__________________

Admiral C322C2 Regent (Restoring)
RCA CTC-7 Pensbury (Restored)
RCA CTC-5 Westcott (Restored)
CRA CTC--4 Director 21 (Restoring)
Reply With Quote
  #179  
Old 04-03-2017, 07:41 PM
Electronic M's Avatar
Electronic M Electronic M is offline
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 9,000
Got an analog VOM with a d'arsonval meter? That ought to capture the variation.
Dirty secret to taking under-chassis measurements with the chassis in the cabinet: get some clip leads connect one end of a lead to a relevant test point and run the other out from under the chassis to your meter probe and slide the chassis back in the cabinet....That method has saved my bacon on sweep and boost troubleshooting a few times.

Also table model CTC-4s have enough harness length (except maybe HV, but that can be addressed) that you can set the chassis up on the floor behind the cabinet with all the under-chassis exposed...For a console like yours if you can find a sturdy box or some such as high off the ground as the chassis shelf then you should be able to pull it up to the back of the set place the chassis on it and make everything reach/accessible.
__________________
Tom C.

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

Reading between the scan lines since the mid 2000's.

Last edited by Electronic M; 04-03-2017 at 07:46 PM.
Reply With Quote
  #180  
Old 04-03-2017, 07:46 PM
SwizzyMan's Avatar
SwizzyMan SwizzyMan is offline
Restoring an admiral c322
 
Join Date: Apr 2015
Location: Orlando FL
Posts: 845
Quote:
Originally Posted by Electronic M View Post
Got an analog VOM with a d'arsonval meter? That ought to capture the variation.
Dirty secret to taking under-chassis measurements with the chassis in the cabinet: get some clip leads connect one end of a lead to a relevant test point and run the other out from under the chassis to your meter probe....That method has saved my bacon on sweep and boost troubleshooting a few times.
I have a voltohmyst, it needs to be calibrated pretty bad. Havent used it in awhile.
__________________

Admiral C322C2 Regent (Restoring)
RCA CTC-7 Pensbury (Restored)
RCA CTC-5 Westcott (Restored)
CRA CTC--4 Director 21 (Restoring)
Reply With Quote
Audiokarma
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 09:44 AM.



Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
ęCopyright 2012 VideoKarma.org, All rights reserved.