The Family DuMont

[Electronic M]

Sounds like you are seeing what is called 'retrace lines'. The set is supposed to turn off the electron gun when it is in between scanning different scan lines or frames (via a 'blanking circuit'), but some sets don't have that circuitry (I can't see that being the case for a Dumont though), and others it is either insufficiently designed not working due to bad components.

BTW if you play a VHS tape or DVD that has macrovision copy protection on it then that will partially disrupt the blanking circuit and place a series of bright dashes on screen.

[CaryLee]

Originally Posted by kramden66

your brightness focus issue and lines which are retrace lines and lack of brightness suggest a weak crt , if you are not planning on running it for hours on end and only an hour or so a day or every other day I would put a brightener on it , you will get better brightness , contrast and less of the lines and control the focus / brightness , if you had a crt tester you could see what it reads , my Dumont has a weak one so I put a brightener on it but added a resistor so its only 7 or so volts , this is enough to improve the picture and not push it that hard , at 7 volts emissions rise to good on mine, a regular brightener could be 8 or 9 volts , If you don't have one I might be able to space one.

as far as the wiggle it could be where you are at in tuning range , if you reduce the agc it may improve this as well and reduce the wobbly effect .

mike

Thank you for the info!

I forgot to mention that the white lines are stationary, if that makes a difference. I still don't have access to a CRT tester/rejuvenator. Almost bought on on EBAY, but then thought I might only use it once on this set and never use it again...I don't know if I've caught the "TV bug" yet..if I have, it's going to have to continue on much smaller sets! If you don't have a spare brightener, if you could tell me what to look for, I see there are tons of them for sale on EBAY pretty inexpensively. My only concern would be blowing out the CRT I have left and then being back to nothing. But if they are pretty safe, it might be worth a shot. It's not like the CRT is going to get better all by itself..and it may be a long while, if ever, before there's anyplace to send it off for rebuild.

I was running the TV off a VCR/DVD combo with RF output..but I can't get the DVD side to work. So I was watching a VHS tape. I remember VHS wouldn't always put out the best picture even on modern color sets, particularly when they started playing around with copy protection.

My DuMont set has a "local/distance" switch on the back which I believe has to do with the "gain". I had it set to "local". When I switched it to "distance", the whole picture would start to roll.

[CaryLee]

Originally Posted by Electronic M

Sounds like you are seeing what is called 'retrace lines'. The set is supposed to turn off the electron gun when it is in between scanning different scan lines or frames (via a 'blanking circuit'), but some sets don't have that circuitry (I can't see that being the case for a Dumont though), and others it is either insufficiently designed not working due to bad components.

BTW if you play a VHS tape or DVD that has macrovision copy protection on it then that will partially disrupt the blanking circuit and place a series of bright dashes on screen.

Thank you! I'll have to take a look at the schematic and see if I can identify the circuit you mention. I was watching a VHS tape, I'll have to take a look and see if it had macrovision. I remember it being a problem with some VCR/TV setups even back in the day when VHS was king. We had to constantly fiddle with the tracking trying to get rid of what looked like interference.

One thing that WAS an improvement today was that I switched around the three 6SN7GT tubes. One is vertical oscillator, one is vertical amp, and one is horizontal AFD/horizontal amp. I noticed that if I "flicked" one of them with my finger, the picture would jump. That seemed to happen to one particular tube no matter what position it is in. Moving it seemed to fix the top of the picture on the CRT "bending"..could be coincidence. Seems like one of the 6SN7GT tubes might have an issue, so I'm going to look around for a few NOS to buy.

[old_coot88]

Cary,
Whatever you do, please hold off on any idea of shooting the CRT with a 'juvinater. It's very easy to wreck the tube, specially if you don't have prior experience using one. If the tube is actually weak (which hasn't yet been proven conclusively), a brightener is the much safer way to go, for a noobster.

[kramden66]

it might be bending at the top because of the tape , tapes have that effect on some sets , the white lines being stationary sound to me like a weak crt , its because you have to push more brightness then required and its showing up .

agreed it wont hurt to try a brightener and if it looks much better you will have your answer , on rare occasions you can run a set with a brightener for lets say an hour , remove the brightener and it might work ok without it after that but that's rare
there are series and parallel brighteners , I can't think at the moment but I think you want a parallel , someone correct me if I'm wrong.

[Electronic M]

If your heaters are wired in parallel you want a parallel brightener, if they are series go with series. Don't use one that is an 'isolation' type unless your CRT has a heater-cathode short.

Retrace lines can be an indicator of, but are NOT definitive proof of a bad CRT and can occur in a set with a perfect NOS CRT if the circuits are malfunctioning, poorly adjusted, or poorly designed.

The blanking circuit is usually a resistor/capacitor network going from near the output of one or both deflection circuits to one of the video stages. It feeds back the retrace portion of the pulse to the video stages turning them off HARD on the retrace.
If those parts have drifted in value or failed it can cause retrace issues. Some sets had the circuit, but it was insufficient or ineffective if the CRT emission changed slightly. If your set has an AGC control (when mis-adjusted it can cause retrace lines) I'd try adjusting it in conjunction with brightness and contrast to see if there is a good compromise that reduces retrace lines.

CRT rejuvinators are a mixed bag. The newer/est ones tend to be gentle and some of them are nearly fool proof, but many of the older ones going up into at least the 60's use 'Atomic blast' (modern VK slang) rejuvination circuits that tend to destroy as many tubes as they help...Though dead tubes that the safer rejuvinators can't help sometimes will be fixed by an 'atomic blast' rejuvinators. Rejuved CRT's don't always last some need a mild rejuv every 5 years and it brings them back to like new, others come back to varying degrees and fall back or below what they were at within hours or days.

[CaryLee]

I took another look at Phil's write up of his DuMont restoration, and saw a photo of the "scan lines", and that is exactly what I'm seeing. Information overload apparently caused brain-fade. I usually remember stuff like that visually.

I also saw how his set suffered from lower-than-normal voltage from the high voltage section, which contributed to a VERY dim CRT initially. His fix involved replacing a bad 270uuf mica cap marked C245 on the schematic. Looking at my order sheet from "JustRadios", I see I ordered a couple of these...and remembered they were just for this purpose. I'll try replacing it in the AM and see what happens. Can't hurt since I already have the cap here.

[CaryLee]

Originally Posted by old_coot88

Cary,
Whatever you do, please hold off on any idea of shooting the CRT with a 'juvinater. It's very easy to wreck the tube, specially if you don't have prior experience using one. If the tube is actually weak (which hasn't yet been proven conclusively), a brightener is the much safer way to go, for a noobster.

Don't worry about the rejuvenator. I'm not even close to seeing one in real life, let alone having one in my hands to fool around with. There's a few other things I'd like to try, involving adjustments and circuitry, first. I'm not even sure I know what I'm doing with that yet...after doing some reading I find I might have gone about adjusting the yoke and ion trap all wrong. And there's a couple of adjustments in the high voltage section that I have no clue about. One is a screw painted red, with a silver screw next to it. I'm going to have to read up some fine print in the Riders and SAMS to see if there's any mention of it.

[CaryLee]

Wow!

I didn't think changing out ONE mica cap would cause such a problem. I had a stable, if slightly dim, picture before. Now I can't get the picture to stabilize for more than a few minutes at a time. Adjusting gets the picture looking great, and then for no apparent reason, I lose it and get..well..the photo will tell the story. So now I have a BRIGHTER bunch of hash.

First picture, before the change of the cap.

Second picture, after.

[earlyfilm]

Originally Posted by CaryLee

I didn't think changing out ONE mica cap would cause such a problem. I had a stable, if slightly dim, picture before. Now I can't get the picture to stabilize for more than a few minutes at a time. . . . .
First picture, before the change of the cap.

Cary, if that first picture is not a composite picture with the CRT image and the cabinet from two different exposures, that is a good picture tube. Back when this set was made, most people watched TV in a semi darkened room! Most 19AP4's had a gray faceplate that absorbed a bunch of light to allow the set to produce a darker black in a lighted room and hide reflections. Even when new, that tube would not be nearly as bright as a modern tube.

I'm using factory numbers for the R113 and I am confused as to what your are talking about. Did you change C-245 the 270 µµf mica capacitor that goes between pin 4 of the 6SN7 and pin F of the horizontal transformer Z-210?

If so, C-245 will affect horizontal sync, but I don't see any way this capacitor could affect vertical retrace in your picture or the brightness (provided it did not change the width of the image.)

Have you replaced the 6SN7 that changed the picture when thumped? This usually is the sign of a shorted tube. If it now is in the sync circuit, it could well be the cause of our problem.

If C-245 is the part that you changed, you need to recheck all your changes for a wiring error, wrong value component or an over heated pin on the transformer while soldering, or a cold soldered joint.

Once you get the set back to working, for either retrace or lack of brightness on a set without traditional sweep blanking, the first thing I would check is the DC restorer.

My first check in the DC restoration circuit would be to measure the 1 meg resistor on cathode and check the voltages on that tube and also try a substitute 6AL5.

Where your retrace only shows at the top of the screen, usually this is caused by a wave shape error on the vertical sweep spike, although I've seen a gassy CRT do this. (The spike is the part of the sweep where the beam moves back to the top and if it slows down near the top, it often will be visible.)
Jas.

[CaryLee]

Originally Posted by earlyfilm

Cary, if that first picture is not a composite picture with the CRT image and the cabinet from two different exposures, that is a good picture tube. Back when this set was made, most people watched TV in a semi darkened room! Most 19AP4's had a gray faceplate that absorbed a bunch of light to allow the set to produce a darker black in a lighted room and hide reflections. Even when new, that tube would not be nearly as bright as a modern tube.

I'm using factory numbers for the R113 and I am confused as to what your are talking about. Did you change C-245 the 270 µµf mica capacitor that goes between pin 4 of the 6SN7 and pin F of the horizontal transformer Z-210?

If so, C-245 will affect horizontal sync, but I don't see any way this capacitor could affect vertical retrace in your picture or the brightness (provided it did not change the width of the image.)

Have you replaced the 6SN7 that changed the picture when thumped? This usually is the sign of a shorted tube. If it now is in the sync circuit, it could well be the cause of our problem.

If C-245 is the part that you changed, you need to recheck all your changes for a wiring error, wrong value component or an over heated pin on the transformer while soldering, or a cold soldered joint.

Once you get the set back to working, for either retrace or lack of brightness on a set without traditional sweep blanking, the first thing I would check is the DC restorer.

My first check in the DC restoration circuit would be to measure the 1 meg resistor on cathode and check the voltages on that tube and also try a substitute 6AL5.

Where your retrace only shows at the top of the screen, usually this is caused by a wave shape error on the vertical sweep spike, although I've seen a gassy CRT do this. (The spike is the part of the sweep where the beam moves back to the top and if it slows down near the top, it often will be visible.)
Jas.

You may have a point about me expecting more from the CRT than it was designed to deliver. I don't have any point of reference to compare to since I never have ever seen this set working before. I'm probably expecting too much from 1950! However, that image of the picture is with the brightness and contrast almost all the way up. Towards the middle of adjustment, it would fade to black. And I will say that the photograph does make the picture appear slightly brighter than it is in real life. But I did take that photo this afternoon, with daylight in the room.

According to Phil's write up of his RA 113, he experienced a dark picture because he wasn't getting the high voltage required. He states he was only getting about 4000 volts, when the tube was supposed to be getting around 12000, I may have misunderstood what he wrote, but he found the waveform associated with C-245 incorrect, which seemed to be associated with the voltage deficiency. I'm not real knowledgeable in this, so I was duplicating what he did.

http://www.antiqueradio.org/DuMontRA-113Television.htm

It did seem to work somewhat. I don't have any way at hand to check high voltage, but I do have some old electrical test gear out in the shed that I'm going to dig out tomorrow. I think on of the testers will test high voltage, but I don't remember how high.

You hit the nail on the head about the C-245 mica affecting horizontal sync. I found that little "extra" adjustment on the chassis, right next to the 6BG6G tube. Once I made the adjustment and got the picture back, it did seem to be a bit brighter. But I could be seeing things, and it was getting dark outside by then.

I don't have any spare 6SN7 tubes yet, nor 6AL5's. I plan on getting a stock together of extra tubes for the set, but haven't had time to to locate and order them all yet. I'll make sure to put 6AL5's on the list of "must haves" too.

This sure is a learning experience! You will probably get a kick out of my next post!

[Kevin Kuehn]

I agree that first picture is actually really good for an old set in what looks like a very well lit room. Any chance you kept the old mica cap you replaced? If so I'd try putting things back to original.

[edit] oops, I see you posted the cure for your problem while I was typing my message. BTW you've done an excellent job of bringing this set back to life. Not an easy task for a first time TV restoration.

[CaryLee]

Here's a good one!

Take a look at the photo and see if you can figure out what's wrong.

I've done that TWICE today! ARGGGGGHHHHHHH!

Gonna go take it apart again and retrieve the adjuster...again!

I did find out there's resistors in there! Another learning experience!

[earlyfilm]

Originally Posted by CaryLee

. . . . However, that image of the picture is with the brightness and contrast almost all the way up. Towards the middle of adjustment, it would fade to black. And I will say that the photograph does make the picture appear slightly brighter than it is in real life. But I did take that photo this afternoon, with daylight in the room.

You just casually mentioned what probably is the best clue yet on your brightness issue.

If the image blooms (it suddenly gets bigger as it dims out) before it goes out, look something restricting the HV current to the picture tube. This is the normal symptom of sudden high voltage drop. The most usual suspects are the 1X2 tubes. And no, you cannot test one 1X2 by switching it with the other one as they work together to form a voltage doubler. *

If he image does not bloom, and the image stays close to the same size, look for the problem in either the video output, DC restorer, brightness control or picture tube circuit or the CRT itself. (The latter is not too likely.)

* If you had a scope, you could confirm that the waveforms and signal level going into the grid of the horizontal output are correct. You really need a known accurate HV meter before you go messing with the HV adjustments.

[old_coot88]

Originally Posted by CaryLee

Here's a good one!

Take a look at the photo and see if you can figure out what's wrong.

I've done that TWICE today! ARGGGGGHHHHHHH!

Gonna go take it apart again and retrieve the adjuster...again!

I did find out there's resistors in there! Another learning experience!

YIKEs dude. That looks like a video IF can. It has nothing to do with horz sync. Hope you can get the slug back to where it was. Hope you haven't turned any of the others.