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
  #1  
Old 11-08-2013, 09:38 PM
Bobby Dip Bobby Dip is offline
VideoKarma Member
 
Join Date: Oct 2013
Posts: 28
Is it OK to run a set without the picture tube?

I'm still looking for a picture tube for my 50's TV.

In the meantime, is it OK to power up the set without the CRT? My concern is the HV might go too high without a load, or the yoke (being inductive) might cause problems. I'm a little short on "TV" experience.

Bob D.
Reply With Quote
  #2  
Old 11-08-2013, 09:40 PM
bob91343 bob91343 is offline
VideoKarma Member
 
Join Date: Nov 2010
Posts: 745
I'd guess it would be okay but I don't know for sure.
Reply With Quote
  #3  
Old 11-08-2013, 09:44 PM
Kevin Kuehn's Avatar
Kevin Kuehn Kevin Kuehn is offline
Workin' Late Again
 
Join Date: Jan 2011
Location: WI
Posts: 3,824
It's standard procedure while aligning some sets. Just make sure you insulate well the end of the high voltage connector.
Reply With Quote
  #4  
Old 11-08-2013, 11:22 PM
Electronic M's Avatar
Electronic M Electronic M is offline
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 14,758
The safest thing is to stick the end of the HV lead in an empty GLASS jar or bottle and tape the wire so that the lead stays in the jar. It is not a good idea to leave the lead hanging such that it can arc to the chassis and or YOU.

Also if the CRT heater is in series with another tube heater you will need to put an equivalent resistance in place of the CRT to get the other tube to light.
__________________
Tom C.

Zenith: The quality stays in EVEN after the name falls off!
What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4
Reply With Quote
  #5  
Old 11-09-2013, 07:35 AM
cwmoser's Avatar
cwmoser cwmoser is offline
VideoKarma Member
 
Join Date: Dec 2009
Posts: 552
Carrying this discussion a little farther, do you see any problems just
removing the 1B3 tubes to remove the High Voltage while working on the set?
I had concerns about protecting the Flyback.

Carl
__________________
CW
1950 Zenith Porthole - "Lincoln"
Reply With Quote
Audiokarma
  #6  
Old 11-09-2013, 12:01 PM
kx250rider's Avatar
kx250rider kx250rider is offline
REAL TVs have TUBES!
 
Join Date: Oct 2005
Location: Los Angeles & Dallas
Posts: 3,239
Depending on what the set is, you should be fine, as long as the yoke is plugged in and the anode wire is WELL protected (as Kevin said) from arcing to anything it might damage, or where it could give you a shock. Or just connect it to any CRT; color or B&W, and ground the aquadag coating of said tube to the chassis. That will dummy-load the high voltage circuit safely.

Charles
__________________
Collecting & restoring TVs in Los Angeles since age 10
Reply With Quote
  #7  
Old 11-09-2013, 12:33 PM
N2IXK's Avatar
N2IXK N2IXK is offline
Technohippie
 
Join Date: Apr 2011
Location: Sittin' on the "Group W" bench...
Posts: 799
Quote:
Or just connect it to any CRT; color or B&W, and ground the aquadag coating of said tube to the chassis. That will dummy-load the high voltage circuit safely.
Just connecting the anode lead to a floating CRT will NOT provide a load on the HV. The return path for the HV is the beam current, drawn from the cathode of the CRT. If the CRT isn't plugged in, there will be no beam current, and no load is presented to the HV supply. The external dag coating provides the grounded side of the HV filter capacitance, not the return path for the HV.

That said, there is no real problem running a chassis without the CRT installed. Obviously, a series heater set will need the CRT heater pins jumped with an appropriate resistor so the rest of the tubes light up. Measurements of CRT electrode voltages may be a bit off, without the tube drawing any current.

Pulling the 1B3 is a good way to disable the HV and render the anode lead safe, but make sure that the 1B3 cap is well away from anything inside the HV cage to prevent arcing.
Reply With Quote
  #8  
Old 11-09-2013, 12:56 PM
old_coot88 old_coot88 is offline
VideoKarma Member
 
Join Date: Sep 2009
Posts: 2,541
Quote:
Originally Posted by N2IXK View Post
Just connecting the anode lead to a floating CRT will NOT provide a load on the HV. The return path for the HV is the beam current, drawn from the cathode of the CRT. If the CRT isn't plugged in, there will be no beam current, and no load is presented to the HV supply. The external dag coating provides the grounded side of the HV filter capacitance, not the return path for the HV.
Correct you are, bro. In addition, a fully charged jug with no bleed-down presents a shock hazard even after the chassis is turned off.
Reply With Quote
  #9  
Old 11-11-2013, 12:21 PM
DaveWM DaveWM is offline
VideoKarma Member
 
Join Date: Feb 2009
Location: Orlando FL
Posts: 5,607
moved my comment to color tv

Last edited by DaveWM; 11-11-2013 at 12:25 PM.
Reply With Quote
  #10  
Old 11-11-2013, 03:46 PM
zeno's Avatar
zeno zeno is offline
VideoKarma Member
 
Join Date: Mar 2013
Location: New Hampshire
Posts: 4,672
Used to do it all the time. Had a HV probe hooked up
& stuffed the anode in a big rubber boot.

73 Zeno
Reply With Quote
Audiokarma
  #11  
Old 11-11-2013, 04:45 PM
stromberg6's Avatar
stromberg6 stromberg6 is offline
VideoKarma Member
 
Join Date: Sep 2004
Location: Ellington,CT
Posts: 465
Never tried that with a B/W set, but have used BIG load resistors for color alignment. Otherwise the voltage would be too high and screw up the process. Maybe as long as the yolk is connected it won't be a problem. Just check the B+ with a meter as you power up the chassis to make sure it's within about 10 percent or better of rated spec. Maybe use a variac to do it. Hope this helps.
Kevin
__________________
stromberg6
Reply With Quote
  #12  
Old 11-11-2013, 05:26 PM
Electronic M's Avatar
Electronic M Electronic M is offline
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 14,758
Another way to do it is to pull the Horizontal output tube. That disables the HV. There are some drawbacks to that though...The set will not draw nearly as much B+ current so you won't get an accurate B+ current measurement for designing a replacement power supply. The other issue is that the AGC circuit (which is like an AVC circuit in a radio only more complex) in some TV sets relies on a pulse from a winding on the flyback which requires the HO tube to be in place....The worse case scenario for this is that the set may not receive any signals fed to it with the HO tube removed(no harm is done to the set though).
__________________
Tom C.

Zenith: The quality stays in EVEN after the name falls off!
What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4
Reply With Quote
  #13  
Old 11-12-2013, 12:01 PM
kx250rider's Avatar
kx250rider kx250rider is offline
REAL TVs have TUBES!
 
Join Date: Oct 2005
Location: Los Angeles & Dallas
Posts: 3,239
Quote:
Originally Posted by old_coot88 View Post
Correct you are, bro. In addition, a fully charged jug with no bleed-down presents a shock hazard even after the chassis is turned off.
Clarification of what I meant:

It's true that there will be HV stored in the tube, and that is whether or not the tube is in use with the beam current loading the HV. In fact, I doubt there's much difference in the danger of stored HV in the CRT, whether being connected or not. Most TVs have no method of bleeding down the HV stored in the tube. That's why in all cases, the person working on the set should ground it out with a clip lead from the dag to a screwdriver when you're done, as I do as a matter of practice in all cases. As far as my reference to "dummy loading" the HV, I mean having the dag grounded will keep the HV from seeking a bad place to discharge into; not regulate it. The regulation of the HV doesn't involve the CRT, so I apologize if I insinuated that it did.

Charles
__________________
Collecting & restoring TVs in Los Angeles since age 10

Last edited by kx250rider; 11-12-2013 at 12:04 PM.
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 03:14 PM.



Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
©Copyright 2012 VideoKarma.org, All rights reserved.