The Family DuMont - Page 9 - Videokarma.org TV - Video

old_coot88 · #**121** 02-12-2014, 11:39 AM

I dunno. Considering the heirloom status of the TV, and unless the CRT is absolutely and equivocally proven weak and needing a brightener, i wouldn't do it. The pics Cary has posted of the CRT's display sure don't look like a weak CRT.
Symptoms of weak emission would include (from a cold start): coming on very dim with a 'silvery' or negative look, then gradually building up over several minutes to a brighter pic.

Kevin Kuehn · #**122** 02-12-2014, 11:45 AM

Yeah, the contrast on the below picture is excellent considering the room lights are on. The dark area's simply can't get any darker than the CRT face color when the set is turned off. The whites look very bright, and there's no visible retrace lines that I can see. IMO it's as good as it can get from an 19AP4. Turn the lights off and you can turn the brightness down accordingly. Kick back and enjoy.

http://videokarma.org/attachment.php...4&d=1392130928

Tubejunke · #**123** 02-13-2014, 01:50 AM

That picture looks wonderful! Nothing like seeing a good working DuMont and you are lucky to have one. Just get some help when moving the thing!

john f · #**124** 02-13-2014, 06:56 AM

Nice job Cary! I'm new to TVs and you're giving me hope. Looks Great!

kramden66 · #**125** 02-13-2014, 11:47 PM

I just remembered although it may not apply in your case , the ion trap if not in the right position would cause less brightness , unsure if you ever checked it or not
mike

old_coot88 · #**126** 02-14-2014, 10:06 AM

GOOD CALL on the ion trap. One of us geniuses shoulda thunk of it earlier.

CaryLee · #**127** 02-14-2014, 12:08 PM

Howdy all,

Thanks for all the kudos on the DuMont! I appreciate it. Working on this set has certainly given me the confidence to do another, though it's more likely to be a tabletop model, unless something else falls into my lap out here in New Mexico.

Thanks for the tip on the ion trap. That is one of the first things I learned about to get the brightness up. The one on my set is just a magnet on a collar with a spring around it, no tightening mechanism, so it's also easy to accidentally knock it out of adjustment with just a touch...which I've done a couple times and then panicked as I wondered for a second why the picture got so dim suddenly.

I've taken a break from the DuMont to work on a few other projects. Doing some remodeling in the house and have to get the engine back in my Jeep Wrangler. It's been a "short block" sitting in the cargo area of our van for a month and a half now, and I've got an off-pavement trip coming up first week of April. AND, we've got nice weather right now...daytime temps in the 60's! Can't beat that for February, particularly considering the hammering the rest of the country is getting from the weather. I have to take advantage of it.

Back to the DuMont for a minute: I do have some NOS 1x2 rectifier tubes for the HV power supply in my mailbox, gonna pick them up this morn and see if it makes any difference when they are installed.

The only major issue I seem to be having with the DuMont right now is that I seem to have the picture well aligned, and in fact pretty good, but slightly off from the best sound alignment. The sound volume doesn't get very high at it's best when I adjust the sound IF cans, and there's plenty of "hum". I've gotten louder and clearer sound when the picture wasn't as good...makes me wonder if I don't have every single video IF can off by the same amount, so I get good picture, but they are too far from the range of the sound IF cans. There does seem to be some correlation, however slight, between picture and sound on this DuMont, even thought they are technically "split".

It will be something to tinker with in the next couple evenings as I finish up some other projects.

I'll certainly keep everyone updated, and thanks again for all the help and encouragement while I've been working on this DuMont! I'm very happy to have it back in the house for the first time in a decade, and operational for the first time in half a century!

old_coot88 · #**128** 02-14-2014, 01:10 PM

Cary,
Unless somebody can advise otherwise, i would hafta say this regarding your sound tracking problem: The problem lies entirely with the sound IF strip, not the video. Any misalignment of the video strip would show up visually (as smearing, ringing, loss of fine detail etc.). Please resist any temptation to touch the vid cans any more.

I would try "walking" the sound cans a bit in one direction, and if tracking gets worse, 'walk' them in the other direction. 'Walking' each slug involves going only a tiny fraction of a turn at a time.

CaryLee · #**129** 02-14-2014, 08:04 PM

Quote:

Originally Posted by old_coot88

Cary,
Unless somebody can advise otherwise, i would hafta say this regarding your sound tracking problem: The problem lies entirely with the sound IF strip, not the video. Any misalignment of the video strip would show up visually (as smearing, ringing, loss of fine detail etc.). Please resist any temptation to touch the vid cans any more.

I would try "walking" the sound cans a bit in one direction, and if tracking gets worse, 'walk' them in the other direction. 'Walking' each slug involves going only a tiny fraction of a turn at a time.

I will definitely try your suggestion. Thank you! I really would rather NOT have to fool with the video strip again if I can help it, at least until I have access to an oscilloscope and signal generator.

I don't know if I ever mentioned that it took about 8 HOURS, over two days, to get the picture to where it is now, strictly going by eye. I'm definitely not enthusiastic about doing that again.

kramden66 · #**130** 02-15-2014, 12:20 AM

you may have to do what I had to do to my Dumont , similar issue with the sound , so I hope I'm correct in what I'm about to say , if not someone correct me ... let the set run and warm up for about 10 minutes , tune the picture to where it looks best and then do what old coot said and go one by one with the sound alignments , eventually you should be able to get them to where the sound is the loudest where you are tuned to a good picture , working with the sound if alignments should be easier then doing the video ifs.

Phil Nelson · #**131** 02-15-2014, 12:50 AM

This kind of divergence is common with "split sound" TVs like this, where the sound signal is picked off fairly early and the audio section has its own series of IF amplifiers, in parallel to the video IF amplifiers, so to speak. (An alternative, slightly more modern design is to pick off the audio signal farther downstream, after the IF amplification has been performed.)

Look carefully at the schematic and your manual's sound alignment instructions, and you should be able to do what old_coot88 says: gently nudge the audio IF alignment to match up with your current video IF alignment, so that they both tune in together. I think you will find it considerably easier than video alignment.

Phil Nelson

old_coot88 · #**132** 02-15-2014, 07:53 AM

Cary,
You gotta realize that the normal video IF bandpass is extremely wide, and the individual cans are actually stagger-tuned to different frequencies within that band.
Whereas the sound IF is tuned to only *one* single frequency and is extremely narrow compared to the vid IF.

This is why no amount of tweaking the vids is gonna shift their tracking 'toward' the sound.

Whereas shifting the sound IF centerpoint relative to the vid will change tracking.

kramden66 · #**133** 02-21-2014, 02:04 AM

here are some pics of the sister to your Dumont , the ra-109

wiseguy · #**134** 02-21-2014, 05:28 AM

on this RA-109 I have please look at the crappy cell phone pics that I took while running out the door, . I though it was my eyes but even my cell phone shows this.
since Everyone is talking about Dumonts and 19AP4.
is there something different about the Phosphors in these tubes?
its perfectly Focused, its just a crappy cell phone picture, and the camera white Balance is fine,
I will take another pic with my Nikon DSLR later afterwork. but for sure with my eyes its Bluish

Phil Nelson · #**135** 02-21-2014, 08:35 AM

One of my cameras makes B/W screens look very bluish. I think some of it has to do with shooting under comparatively yellowish indoor lights. The camera does some kind of color average (is that the right term?) with the room as a whole and gets the colors right for the cabinet, drapes, etc, but the screen comes out too blue. It's so blue that, for photos I want to use on my website, I sometimes cut out the screen portion and convert that to greyscale so that it doesn't look ridiculous. This effect is true of all my B/W sets, with various CRTs; they all display shades of grey to my eyes but the camera turns them weirdly blue.

Try turning out all of the room lights and taking a photo of only the screen. Then turn on the room lights, photograph again, and compare blueness of the screen in both shots.

I'm not saying that phosphors don't have different colors, only that I've seen this very obvious effect when shooting photos under warm indoor lights.

Phil "not a serious photographer" Nelson
Phil's Old Radios
http://antiqueradio.org/index.html