DuMont "doghouse" troubles.

Kyle Steck · Posted: Oct Thu 22, 2009 3:44 am

Hello again, I am just updating the topic of my DuMont television restoration.

I am having the set serviced by someone else. I have replaced ALL of the wax old paper caps and filters and even the flyback transformer. He had gotten the set to work for 10 minutes, he was actually watching it! But, then after that 10 minutes the picture disappeared and there is now a one inch wide vertical line that spans the tube. We are both stumped, everything measures correctly, all resistance measurements are in range, just no picture. What could be causing this? We also replaced that resistor that is known to go bad in the HV cage. Still nothing. Any help is appreciated!

Tom Albrecht · Posted: Oct Fri 23, 2009 5:58 am

Kyle,

You may have a problem in the horizontal coils of the deflection yoke or the windings on the flyback transformer that drive the yoke. Check the wiring to the yoke. Substituting a different yoke may also be a useful check. Check the horizontal width and linearity coils and the wiring to them.

Also, check the voltages in the horizontal output and damper stages to see if everything is where it should be.

If you have a scope, check the frequency of the horizontal oscillator. If this is not running at the right frequency, check the components in the horizontal oscillator.

Good luck!
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Tom K6VL

Kyle Steck · Posted: Nov Mon 02, 2009 5:19 am

The damn thing works!

Apparently the new old stock flyback I put in, blew out, meaning the windings shorted. Fortunately the old flyback is good and is working in the set! The only problem it has now is that the middle of the picture is pulling to the left horizontally. So whatever is on the screen is stretched. What could be causing this?

Thank you for the help!

Tom Albrecht · Posted: Nov Mon 02, 2009 6:22 am

You've got three adjustments on this set to work with:

1. width
2. horizontal centering
3. horizontal linearity

Width and centering are self-explanatory.

Linearity is the adjustment that can be used to even out any tendency to stretch on one side while compressing on the other.

First try the width and centering controls, and make sure they have the intended effect. Then try the same with linearity. Linearity can be tricky to adjust unless you have a test pattern with a grid pattern. In the absence of that, lettering on the screen in commercials and movie credits can work. If you have a DVD player, bring up a suitable picture and pause there while you make adjustments.

If you find that the adjustments don't work, check the wiring of the width and linearity coils, and the components directly around them. Also make sure you have a good damper tube and horizontal output tube.
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Tom K6VL

Kyle Steck · Posted: Nov Thu 05, 2009 4:14 am

After running the TV and making a few adjustments, it's looking pretty excellent! Only one more thing. There seems to be some kind of shadow effect going across the screen if the imagine on the screen scrolls, like the camera moves. What could be causing this problem?

Tom Albrecht · Posted: Nov Thu 05, 2009 4:53 am

Hi Kyle,

Not quite sure what you're describing, but let me make a guess: You've got a "wave" that moves slowly through the picture from bottom to top.

If that's what it is, it's 60 Hz or 120 Hz in the power supply due to a bad electrolytic filter capacitor somewhere in the power supply.

Another possibility is interference from a nearby DTV converter or cable box.

Or you may be seeing something entirely different. Try to give us a little more detailed description of what you're seeing.
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Tom K6VL

Tom Schulz · Posted: Nov Thu 05, 2009 6:47 am

I have seen an effect where the picture is darker than it should be immediately the the right of something bright. It is most noticeable when there is white lettering scrolling up the screen. That can be caused by a capacitor in the video circuit that is too small. A bad electrolytic can be way small but not quite gone. It is also possible to replace a capacitor with the wrong value. Getting one that is 1/10 th of the correct value is easy to do and easy to not see.

hoffies2 · Member Joined: 08 Feb 2007 Posts: 4123 Location: USA

The person that doing the servicing should be of help? You have a phasing problem that can be caused by outside interference, among other things suggested above. Smile

You may never get these old TV's 100%.

philsoldradios · Posted: Nov Thu 05, 2009 7:39 pm

What are you using as a video source?

I'm currently finishing up a DuMont RA-103. A set without AGC responds differently to some signals than one which has AGC.

If you can give a more detailed description, perhaps others can help tell whether you have a problem, or you're seeing some momentary effect that's normal for this kind of set.

Phil

Kyle Steck · Posted: Nov Sat 07, 2009 4:13 am

Will a 12LP4 work in this set?

Mr. Detrola · Posted: Nov Sat 07, 2009 4:21 am

Yes, you have to change the HV connector to the correct type and adjust mounting hardware/yoke position so the tube is physically in the right place.
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Dennis

Kyle Steck · Posted: Nov Sat 07, 2009 4:23 am

How much is a working 12JP4 worth with an ion burn?

Tom Albrecht · Posted: Nov Sat 07, 2009 6:35 am

Hi Kyle,

Are you sure that you need a new CRT? Not quite clear what effect you are seeing from the above description.

I'm not sure what a 12JP4 would go for, but if the ion burn isn't bad, and the tube is nice and bright, I could imagine $50-$100. One with no defects would go higher.
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Tom K6VL

Eric H · Posted: Nov Sat 07, 2009 10:40 am

Bill Cahill · Posted: Nov Sat 07, 2009 3:36 pm

Dumonts used a straight back, and, will have no problem accommodating an ion trap.
Bill Cahill
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Kyle Steck · Posted: Nov Sun 08, 2009 2:22 am

Oh I don't need a knew one, I was just curious as to what would replace a 12JP4 due to the fact that they cannot be rebuilt. My 12JP4 is good, but I would like to use my set very often...

Kyle Steck · Posted: Nov Thu 19, 2009 5:04 pm

Does anybody know what the knob says for the selector? I am having labels made for when I restore the cabinet. My label for that switch is worn off. All I can read is "phono" "FM" and then the rest is worn off. Can someone please let me know what the other two setting abreviations are?

Thank you, Kyle

philsoldradios · Posted: Nov Thu 19, 2009 9:10 pm

Here are some of the decals on my Meadowbrook RA-103 cabinet.

Let me know if you make a decal set. My cabinet has serious problems (not seen here) that will require a total refinish.

http://antiqueradio.org/DuMontRA-103Television.htm

Did someone tell you a 12JP4 can't be rebuilt? The CRT in my set has a sticker from a rebuild shop labeled 12JP4. It also appears to use a different gun, requiring an ion trap. Go figure. Anyway, it's very bright, so I'm keeping it, whatever it is Smile

Phil Nelson

Kyle Steck · Posted: Nov Fri 20, 2009 5:56 pm

I just added that set you own to my wish list Very Happy

The people I am having make my labels are having trouble peeling them from the rest of the sheet. They are being cut from gold vinyl. I already have the DuMont label cut and it is pretty darn close to the original.

rdusel · Posted: Nov Fri 20, 2009 8:06 pm

Good Afternoon Gentlemen!
I'm also starting a rebuild of an RA103 doghouse and was looking for a 12JP4 as mine has lost it's vacuum. The filament is intact but the getters are white so I know what will happen when I power it up.
I was told that the 12JP4 can not be rebuilt because it is pyrex and there are no more pyrex necks available, just the regular glass necks.
Maybe they were available in the past?
I would also be interested in a label set if your supplier starts offering them.
Thanks guys!
Rob