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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. |
#2
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I'd guess it would be okay but I don't know for sure.
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#3
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It's standard procedure while aligning some sets. Just make sure you insulate well the end of the high voltage connector.
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#4
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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.
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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 |
#5
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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
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CW 1950 Zenith Porthole - "Lincoln" |
Audiokarma |
#6
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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
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Collecting & restoring TVs in Los Angeles since age 10 |
#7
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Quote:
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. |
#8
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Quote:
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#9
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moved my comment to color tv
Last edited by DaveWM; 11-11-2013 at 12:25 PM. |
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Used to do it all the time. Had a HV probe hooked up
& stuffed the anode in a big rubber boot. 73 Zeno |
Audiokarma |
#11
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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
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stromberg6 |
#12
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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).
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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 |
#13
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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
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Collecting & restoring TVs in Los Angeles since age 10 Last edited by kx250rider; 11-12-2013 at 12:04 PM. |
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