Pix Tube Replaced - Videokarma.org TV - Video

andrefranc · #1 10-27-2005, 01:13 PM

I just replaced the pix tube and still have no pix, no brightness at all on the screen. There is 51V dc on the cathode, .9 v on the grid, 318 v on the screen grid and 9 KV on the anode. What could be wrong? or did I get a bad pix tube (it is a 16" B&W tube). It checks OK with the CRT tester.

jpdylon · #2 10-27-2005, 01:23 PM

check your video output circuits a bad video output tube or associated circuits will leave you with a dark screen.

Is your HV ok? what are you getting at the HV anode? Checked your HV rectifier lately?

andrefranc · #3 10-27-2005, 03:16 PM

Video Output Tube Is Ok And I Have 9kv At The Anode So Should Be Enough For Some Light On The Screen I Would Think. The Old Worn Out Pix Tube That Was In The Set Gave Some Picture But Now After Changing The Pix Tube There Is No Brightness At All.

jpdylon · #4 10-27-2005, 03:24 PM

Are the pix tube numbers the same? Sometimes a replacement tube doesn't have exactly the same pin layout as the old tube. Occasionally the screen or grid pins may be moved one over. I would see if the tube came with a pin diagram, or look it up online if you can. Compare it with the pin layout on the socket. If the old tube worked it may just be pin relocation.Ther also can be instructions for adding a jumper on the tube to comply with the way the old tube was used. Were there any jumpers on the back of the crt that you may have missed. Also don't neglect old connectors on the crt socket. I would crimp them a little to ensure a good connection.

Sorry if these sound like an insult. I'm not trying to challenge your experience in any why, just trying to think of all the possibilities.

***Eric H*** · #5 10-27-2005, 05:30 PM

Does the tube use an Ion trap?
If so it could be misadjusted, on the other hand if your old tube used a trap and your new one isn't supposed to that would cause a problem too.
What is the tube number?

The trap is a small magnet mounted on the neck of the tube near the base cap.

Eric

andrefranc · #6 10-27-2005, 09:11 PM

Both tubes are 16wp4 and I have tried the ion trap. The tube checked funny with the ion trap on so removed it and then it check ok. My checker said some old tube would check different unless the ion trap was removed. I will take a closer look at the socket connections but they seemed to be ok and the pin layout seems to be the same and as both tubes have the same tube number. One reading for leakage on my checker (the 'A') setting said it should be over 4meg and was only 3.5meg but doesn't seem like that is enough difference and the checker could be off some as is old.
John

Steve K · #7 10-27-2005, 10:21 PM

John:

Considering that the voltages seem to be correct I have to agree with Eric that the ion trap might be misadjusted. Don't be afraid to move it around on the neck of the tube while watching the screen. Sometimes they need to be in a very specific spot to get any picture at all. If it still does not work then pull it off and reverse it and try again.

Steve

Jonathan · #8 10-28-2005, 12:23 AM

I had to move the ion trap of my 10BP4 all around to get some sort of picture. At first it seems as if something is wrong but if you move the ion trap around up and down, even changing polarity, a picture will come up if everything is good to go. I'd love a 10FP4.

Jonathan

daro · #9 10-28-2005, 02:56 AM

I was also thinking about the ion-trap magnet adjustment which was used on just about all CRT's made before 1958.

andy · #10 10-28-2005, 10:33 AM

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andrefranc · #11 10-28-2005, 07:44 PM

I tried moving the ion trap around tonight and I was working in the garage with very little light and noticed a bright blue glow in the neck of the tube that would change intensity and position with the positioning of the ion trap. Seems like the tube is no good as probably has gas in it and I have had it now some ten days. Before this I always was working in real bright light and did not notice the blue glow. I suppose the tube got damaged in shipping but I'm not sure.

***Eric H*** · #12 10-28-2005, 11:16 PM

A blue glow can sometimes be normal, I have observed this sometimes when just testing a CRT on the checker, if the whole neck is glowing blue however that would be a different matter..

You said the tube checks OK for emisson using a CRT tester? If so then it probably should work. Are you certain you have enough high voltage at the second anode connector?

Also make sure the aquadag coating on the tube has a good connection to ground. (this isn't a metal shell tube is it?)

andrefranc · #13 10-29-2005, 06:47 AM

The blue glow in the neck of the pix tube moves around a lot when moving the ion trap and in some positions it is not very noticeable at all. I had only 5KV at first and then found the two 1X2's real weak and replaced them, now I have about 9KV. It goes to 14KV when not connected to the pix tube. Wouldn't 9KV be enough to light the tube?

frenchy · #14 11-11-2005, 12:22 PM

You sure the replacement tube needs a ion trap? I got a set once with a 10bp4 I think that had the trap put on it (was a replacement tube) and could not get any picture. Till I figured out the guy who replaced the tube just swapped the trap on from the other tube and THIS tube didn't USE a trap. Took it off and it worked. This was an aluminized one I guess that didn't use it.

*Bill Cahill* · #15 11-11-2005, 03:36 PM

On your 16" tube did you say you were getting 9,000v on anode? Sounds like hv is low. Should be around 13,000v. Could be your horiz. osc. is running either too high frequency, or too low frequency, not properly driving horizontal output, which would then accordingly lower the hv. What brand, and model set do you have? Also, chassis no?