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 Post subject: Re: Admiral 19A11 schematic (new questions)
PostPosted: Jun Tue 18, 2019 10:05 pm 
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Notimetolooz wrote:
If you are getting a picture on the CRT you probably have H.V. I was thinking that you have too much and that was causing the arcing, but it isn't very likely. Did you try looking for the location in the dark?
There could be something arcing internally.
You very much could have two separate problems.
Vertical linearity? I don't see that control on the schematic. Have you replaced any tubes?

The vertical linearity control is a production change. See here: https://www.antiqueradio.org/art/AdmiralTelevisionChassis19A1Schematic.jpg


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 Post subject: Re: Admiral 19A11 schematic (new questions)
PostPosted: Jun Tue 18, 2019 10:11 pm 
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Electronic Memory wrote:
Try to stop the arcing. If the lead is long you can shrink a small diameter heat shrink over the lead up to the solder connection then slip a larger diameter piece just longer than the solder joint onto the lead slid back against the cap body, then solder the joint slip the big diameter over the exposed joint and shrink it. You can also use silicone caulk as an insulator if need be. If you stop the arcing but the HV or focus still are unstable the first thing you should do is track down a HV probe...I just saw one with built in meter for $12 at a hamfest. They are out there cheap if you look. Some problems are only practical to solve with the right tool.

Did you use ceramic or film dielectric caps for the new replacements in the sweep/HV? Ceramic caps need to be double the capacitance of the original paper caps or vertical non-linearity or insufficient height will result. Film caps should be used in the HV and deflection if at all possible.

Do you have a test pattern generator designed for TV repair? If so try injecting video past the detector and see what the picture looks like. If it is good detector, tuner, IF and AGC (if it has AGC) are suspect. If video is bad video amps, CRT/CRT HV and bias circuits are suspect.



I used these caps: https://www.justradios.com/ASCcapacitors.html


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 Post subject: Re: Admiral 19A11 schematic (new questions)
PostPosted: Jun Tue 18, 2019 10:21 pm 
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Yes. I just found out about the production change. So the schematic you posted earlier is not correct.
ASC caps are fine.
If need be you can put together a circuit to measure the H.V. A similar 7 inch set by Hallicrafter has instructions in the service guide, basically a string of 10 Meg resistors in series and an ammeter. It isn't good enough for larger CRTs.
I take it the wire that went to near the control case has been corrected.

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 Post subject: Re: Admiral 19A11 schematic (new questions)
PostPosted: Jun Wed 19, 2019 5:59 pm 
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What voltage rating ASC caps did you use? Some are rated 6 KV, some are 10 KV.
I noticed that in some locations in this set may be at 6.5 KV, so the 10 KV would be the safer choice.

More info about the H.V. measuring circuit. Five 10 Meg resistors are connected in series. That makes a 50 Megohm resistor. I would recommend at least 1 W and 2 W would be better (half watts are not rated for the 1000 V that could be across each one). Using 1 % resistors would help accuracy. Mount them in a straight line end to end on a strip of insulating material like acrylic plastic or phenolic. Connect one end of the string to the positive terminal of a 150 micro-ammeter, (that is 0.15 ma.). I would not use a DMM. Ground the other end of the meter. Attach the other end of the resistor string to the point to be measured. 100 microamps corresponds to 5 KV. This set up will not work well for the much higher anode voltages found in TV with larger screens, it would load the circuit too much.

I'm wondering if you were able to see any arcing?

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 Post subject: Re: Admiral 19A11 schematic (new questions)
PostPosted: Jun Wed 19, 2019 6:47 pm 
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Out of business until a replacement 6SL7GT arrives. Vertical went to really squished so I tested the tube and half is dead. Maybe the reason I couldn’t get the picture high enough with the control all the way up. The arcing will still be an issue. Sometimes it seems as if it’s inside the horizontal centering control, but as mentioned earlier, it’s been taken apart and thoroughly cleaned. About the HV caps, I did use 6000 volt caps since that was what was there before. I wouldn’t think this would cause arcing?


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 Post subject: Re: Admiral 19A11 schematic (new questions)
PostPosted: Jun Wed 19, 2019 10:48 pm 
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According to Riders, the DC voltages on the CRT deflection plates is 6000 V, that is on one side of four of the ASC caps. The DC voltage on the deflection output tube plates is about 250 V. So the difference is 5750 V. If the cap rating (6KV) is working voltage that may be OK. If it is 6000 V maximum, then that is cutting it a bit close. Not sure how the original caps were rated.
Riders says that the voltage on pin 2 of V13, the 1B3 H.V. rectifier, is 6500 V. There is only a 10K resistor between that and C56, that won't drop much voltage so the voltage there may be even closer to the limit for the cap. Every once in awhile a new part doesn't work right.
So if the H.V. is unusually high there may be a problem with the caps breaking down internally.
I think Phil Nelson used the 6KV caps.
We don't want to jump to a conclusion however. There might be a crack in the insulation of a pot where a carbon track would be hard to clean out. The tube sockets are often places where problems with voltage breakdown happen. Maybe the 1B3 socket or the CRT socket. Those sockets must be very clean and dry. It is important to localize the breakdown.

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 Post subject: Re: Admiral 19A11 schematic (new questions)
PostPosted: Jun Wed 19, 2019 11:10 pm 
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Yes, I used 6KV caps and insulated their leads. No problems with arcing on/around those components.

What have you done to stop the arcing from your 6KV cap's lead? Seems like insulation should cure it. It's possible to have more than one problem at a time, of course. But visible arcing is a gross problem that you should cure regardless. And fixing that should reduce the problem domain, at least :)

Phil Nelson
Phil's Old Radios
https://antiqueradio.org/index.html


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 Post subject: Re: Admiral 19A11 schematic (new questions)
PostPosted: Jun Thu 20, 2019 4:35 pm 
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[quote="philsoldradios"]Yes, I used 6KV caps and insulated their leads. No problems with arcing on/around those components.

What have you done to stop the arcing from your 6KV cap's lead?

1. Removed, cleaned and reinstalled the horizontal centering control.
2. Covered the very small exposed portions of the high voltage cap leads with liquid electric tape.
3. Inspected for any sharp wire ends. Didn't really find any but resolver or clipped some anyway.
4. Cleaned the other controls with De-oxit.
5. Cleaned the leads to the picture tube socket. Sometimes I could swear that the snapping sound was coming from above the chassis but I never saw any arcing here.

The arcing seemed to go away for a while so I thought it was cured. When it returned it looked like it could be happening inside the horizontal centering control. Now I'm waiting on a tube so I don't want to do any more testing until the new tube arrives. (No vertical deflection).

Thanks for your help!


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 Post subject: Re: Admiral 19A11 schematic (new questions)
PostPosted: Jun Thu 20, 2019 5:00 pm 
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Some electrostatic sets develop arcing Inside the tube sockets...6kv is really pushing the insulation ratings of octal sockets.


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 Post subject: Re: Admiral 19A11 schematic (new questions)
PostPosted: Jun Thu 20, 2019 5:22 pm 
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You could pull the socket off the CRT and check things that way while you are waiting for the tube. No harm on an electrostatic set.
It would eliminate the rare possibility that the CRT tube base was arcing for one thing.

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 Post subject: Re: Admiral 19A11 schematic (new questions)
PostPosted: Jun Fri 28, 2019 2:09 am 
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Attachment:
B6D0A75D-5160-4DFB-9D85-05231D8F3BC9.jpeg
B6D0A75D-5160-4DFB-9D85-05231D8F3BC9.jpeg [ 253.98 KiB | Viewed 515 times ]
New tubes arrived today. Here’s what the picture looks like. I’m still getting an arc every now and then. Still needs some work. Extra credit if you can name the movie. :D


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 Post subject: Re: Admiral 19A11 schematic (now with picture)
PostPosted: Jun Sun 30, 2019 3:23 am 
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I have replaced a few more resistors. No change. Still no response from the vertical linearity control. The picture is pretty good but objects that are circular still look a bit like pears. Arcing is very rare now. Once in three movie sessions.


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 Post subject: Re: Admiral 19A11 schematic (now with picture)
PostPosted: Aug Fri 23, 2019 3:38 am 
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Steve,
Did you ever solve the intermittent arcing issue? I've got a 17T11 which is very similar to the 19A11, and it's got a similar issue to what you describe. I hear a crack from the HV cap area and the picture gets disturbed then comes back.
Just curious.
Thanks.


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 Post subject: Re: Admiral 19A11 schematic (now with picture)
PostPosted: Aug Fri 23, 2019 4:29 am 
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I guess I would have to say no, since I didn’t do anything or determine the cause, but it hardly ever arcs now. In almost daily use it has arced maybe twice in three or four weeks.

Steve Chambers


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 Post subject: Re: Admiral 19A11 schematic (now with picture)
PostPosted: Oct Wed 16, 2019 11:21 pm 
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I still don’t have enough vertical. It’s especially noticeable now that the chassis is back in the cabinet. I’ve replaced everything I can think of. Unless someone has an idea I’m going to move on to the next project. The set is watchable but it should definitely have more height.

Steve Chambers


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