Videokarma.org

Go Back   Videokarma.org TV - Video - Vintage Television & Radio Forums > Early B&W and Projection TV

We appreciate your help

in keeping this site going.
Reply
 
Thread Tools Display Modes
  #16  
Old 12-06-2017, 09:10 PM
kramden66 kramden66 is offline
VideoKarma Member
 
Join Date: Nov 2010
Location: Rockaway, NJ
Posts: 1,196
Yes I figured that it was pin 1 because that's where the connection from the IF section comes to the video tube just like the admiral , it uses pin 4 for the sane connection.
It is interesting to note that pin 1 is the spot where the voltages are the most crazy , should be 1 volt and I have 18 volts .
Reply With Quote
  #17  
Old 12-06-2017, 09:40 PM
Kevin Kuehn's Avatar
Kevin Kuehn Kevin Kuehn is offline
Workin' Late Again
 
Join Date: Jan 2011
Location: WI
Posts: 2,853
That doesn't sound right. You better double check the other pin voltages on that 6AH6. If you do inject video into pin 1 you might want to go through a .1uf cap.

Last edited by Kevin Kuehn; 12-07-2017 at 01:43 AM.
Reply With Quote
  #18  
Old 12-07-2017, 01:03 AM
kramden66 kramden66 is offline
VideoKarma Member
 
Join Date: Nov 2010
Location: Rockaway, NJ
Posts: 1,196
The other pin voltages are correct , I can try another tube but that's probably not the problem .
Btw the pin reads 0 if the tubes pulled .
Reply With Quote
  #19  
Old 12-07-2017, 01:42 AM
Kevin Kuehn's Avatar
Kevin Kuehn Kevin Kuehn is offline
Workin' Late Again
 
Join Date: Jan 2011
Location: WI
Posts: 2,853
I looked at Riders and they say -.5V. on pin 1. Sams shows with their dotted lines and x's an optional circuit for the cathode(contrast control)circuit. Do you have the simple pot in series with the cathode to ground, or do you have the version with all the extra's?

Make sure that 1M resistor from grid to ground hasn't drifted way up in value.
Reply With Quote
  #20  
Old 12-07-2017, 12:05 PM
kramden66 kramden66 is offline
VideoKarma Member
 
Join Date: Nov 2010
Location: Rockaway, NJ
Posts: 1,196
I will recheck that 1m resistor , as far as the contrast circuit I will have to check it , I thought those x marks were from a former person who marked them on the schematic while working on a set I didn't realize it was an alternate circuit , What the alternate circuit is I'm unsure.
Reply With Quote
Audiokarma
  #21  
Old 12-07-2017, 12:16 PM
jr_tech's Avatar
jr_tech jr_tech is offline
VideoKarma Member
 
Join Date: Sep 2009
Posts: 3,631
Quote:
Originally Posted by kramden66 View Post
The other pin voltages are correct , I can try another tube but that's probably not the problem .
Btw the pin reads 0 if the tubes pulled .
Tube may have grid emission.

jr
Reply With Quote
  #22  
Old 12-07-2017, 12:51 PM
kramden66 kramden66 is offline
VideoKarma Member
 
Join Date: Nov 2010
Location: Rockaway, NJ
Posts: 1,196
It didn't show on the tester so will try another tube but how could this tube knock out the audio too ?
Reply With Quote
  #23  
Old 12-08-2017, 07:22 PM
kramden66 kramden66 is offline
VideoKarma Member
 
Join Date: Nov 2010
Location: Rockaway, NJ
Posts: 1,196
All I was able to do was put a new tube in and it's the same , what I didn't know was that pin voltage varries with the rotation of the contrast control , unsure if it should do that
Reply With Quote
  #24  
Old 12-08-2017, 08:22 PM
Kevin Kuehn's Avatar
Kevin Kuehn Kevin Kuehn is offline
Workin' Late Again
 
Join Date: Jan 2011
Location: WI
Posts: 2,853
What's the pin 1 voltage range with contrast turned from end to end? While you're at it measure the voltage range on the cathode too. Have you replaced the .1uf cap between the detector and pin 1 of the video amp?
Reply With Quote
  #25  
Old 12-09-2017, 11:44 PM
kramden66 kramden66 is offline
VideoKarma Member
 
Join Date: Nov 2010
Location: Rockaway, NJ
Posts: 1,196
With contrast rotated for full contrast pin 1 reads -3.1 volts , pin 7 the cathode reads 171 volts , with contrast turned down all the way pin 1 reads 18 volts , pin 7 the cathode reads 27 volts ...... Yes I changed the .1uf , perhaps the new one is no good ?
I did notice SAMs voltage readings are taken with focus control counter clockwise , this I didn't try .
What I will try is injecting video from a DVD into pin 1 and see what happens .
Reply With Quote
Audiokarma
  #26  
Old 12-10-2017, 01:20 AM
kramden66 kramden66 is offline
VideoKarma Member
 
Join Date: Nov 2010
Location: Rockaway, NJ
Posts: 1,196
Well I hooked to pin 1 with a .1uf and plugged it into a DVD player , I have an image , there are bars on the left side of the screen but that can be dealt with later , the first DVD player I used the image was ok but when you tried to put more black into the image it would cause black lines to reach across from the left and turn it higher it was like overloaD and smeared , so I tried a different player and a better image that if you turn the contrast up you get blacks and if up all the way a slight overload in the whites and a buzz in the sound , a video type buzz.
So it would appear that what ever is wrong it is before the video tube , I will try further but if I give up I can just feed to the video and audio , question is what would happen if I reduced the .1 to a .01 ? What would happen if I went from .1 to.5 ? Any ideas ?

Last edited by kramden66; 12-10-2017 at 01:28 AM.
Reply With Quote
  #27  
Old 12-10-2017, 01:33 AM
Kevin Kuehn's Avatar
Kevin Kuehn Kevin Kuehn is offline
Workin' Late Again
 
Join Date: Jan 2011
Location: WI
Posts: 2,853
So with the contrast control around center, pin 1 is not too far off from the 1 volt Sams calls for? The coupling cap value should only affect the video frequency response. No harm in trying other values, but you can assume .1uf is good because it's the coupling value used before and after the video amp.

Last edited by Kevin Kuehn; 12-10-2017 at 01:36 AM.
Reply With Quote
  #28  
Old 12-10-2017, 09:36 PM
kramden66 kramden66 is offline
VideoKarma Member
 
Join Date: Nov 2010
Location: Rockaway, NJ
Posts: 1,196
Just to note the voltages on the 6ah6 are the same when feeding the video into the tube and they read the same at both ends of the contrast control .
Problem has to be before or at the 12au7 because that's where the picture and sound splits and there's no sound , only sound that can be heard is a buzz in the audio when contrast is at full and there's a slight overload on the screen plus way to black.
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 12:40 PM.



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