View Full Version : Dumont RA-104


Radiotronman
09-11-2016, 09:57 PM
I've been looking for a Dumont tv for a long time and one finally appeared before me. A friend I restored a Predicta for told me he had a friend with tvs and radios and wanted some restored. I contacted him and after talking awhile, he told me he had a Dumont Wellington, model RA-104. I really wanted a round CRT Dumont, but I'd take any Dumont I could find. This set has the 15DP4 CRT and seperate am radio chassis too. It's cabinet is in great condition with only a few small scratches. It also has the three speed record player. To say I'm excited to have this is an understatement. I've got several projects for people lined up ahead of it, but can't wait to get to this fine day! The picture is after I got it home with all chassis removed.

Radiotronman
09-11-2016, 09:58 PM
Here is the cabinet with the doors closed. It is a very well made cabinet and very heavy, without the chassis in it.

DavGoodlin
09-12-2016, 01:22 PM
Here is the cabinet with the doors closed. It is a very well made cabinet and very heavy, without the chassis in it.

My RA-105 Sussex is pretty close in heaviness. Be careful moving yours. I broke my CRT - it was unsecured on its crane rail and slid out as I lifted it off my truck. Another V-K member has a complete RA-105 but its in Wisconsin. I would buy the entire set just for the CRT. I also have an RA-103 Savoy parts set but sold the CRT to another V-K'er for his doghouse.

Radiotronman
09-12-2016, 10:08 PM
I checked the CRT to see if it is good, even though I was told it was. It came way up into the green on my tester. I put the multiple chassis back into the cabinet and put the knobs on until I'm ready to begin restoration on it.

Radiotronman
09-21-2016, 09:34 PM
While I was looking at my Dumont and cleaning tubes, I noticed this wood bracket at the bottom with a few screws. Nothing seems to be missing on the chassis. Was this a mount for some kind of aerial antenna or what?

Tim
09-21-2016, 11:06 PM
During shipment from the factory, the yoke and focus coil assembly were fastened there in order to relieve stress on the neck of the CRT while shipping. When delivered to the customer, the installer would remove them, install over the neck of the crt and make final adjustments.

Radiotronman
09-21-2016, 11:41 PM
Interesting, that makes sense, thanks!

Radiotronman
10-12-2016, 01:56 PM
Just ordered my focus potentiometer to replace the one on my set. It's a 1k, 25 watt wirewound control. Surplus Sales of Nebraska had them for only $8. I also replaced the .05@1000v cap and the .035@1000 cap; since I had them on hand. I write down every cap I need to order, over 40 paper caps and 20+ electrolytics. Does anyone know what to replace the paper tubular caps in the chassis listed as 1.6 ohm caps? What are these? I've never seen them in sets before and what should I replace them with? They are like dyed on the sams as C4 and C5.

Kevin Kuehn
10-12-2016, 02:33 PM
Shown on the schematic as polarized, so I suspect they are large mfd, low voltage electrolytic type? Apparently 1.5 ohms is their impedance at 120 hz. Using the below calculator I came up with 880 mfd to get close to 1.5 ohms. Looking at that Aerovox part number(PRS6/1000) I'm going to guess they're 1000 mfd @ 6v. I'll see if I can find that AV number in an old catalog.

http://www.allaboutcircuits.com/tools/capacitor-impedance-calculator/

Kevin Kuehn
10-12-2016, 02:46 PM
Here's a Radio Master listing for those Aerovox PRS series. Oddly they don't list the complete part numbers. Maybe check and see if the 1000 mfd @ 6v fits the physical dimensions of what's in there.

http://i452.photobucket.com/albums/qq245/Kuehn/VK%20Pictures/1.520ohm20caps20001_zpsbvfewcew.jpg?t=1476211434

Electronic M
10-12-2016, 03:14 PM
IIRC the 104 is similar to the RA-103...I have a Stromberg-Carlson TV-12 chassis set that is a rebadged Dumont RA-103.....In the Stromberg's sam's that is on the ETF schematics page it lists the capacitance and voltage of those lytics...They are low voltage (IIRC 6 and 25V) high capacitance parts...You can easily find spares in junk SS gear.

Radiotronman
10-12-2016, 03:20 PM
Great info guys. I wonder how critical the value is, given how high the capacitance they are?

bandersen
10-12-2016, 03:26 PM
I wouldn't stray too far from the stated values. These are usually used on the centering controls with 1,000uF for the vertical and 250uF on the horizontal. You really don't want any hum or the image will ripple.

Kevin Kuehn
10-12-2016, 03:30 PM
Interestingly if you look at C6 on the Sams parts list(vertical bypass), they actually listed that one as 2000 mfd @ 6v. Probably DuMont overkill?

bandersen
10-12-2016, 03:39 PM
I've done sets with 2,000uF too. Motorola and a Sentinal IIRC. 2200 uF works just fine for replacing those.

Radiotronman
10-12-2016, 04:56 PM
I've got a bunch of these, 2200uf at 35v. Will these be ok?

Radiotronman
10-12-2016, 05:06 PM
Bob, what would you use for C4 and C5?

bandersen
10-12-2016, 05:16 PM
1,000uF rated for 16 volts or higher. Low ESR types if possible.

2,200 will result in an impedance of 0.6 ohms. Probably fine. I think using too small would be an issue but not larger. No harm in trying them.

Kevin Kuehn
10-12-2016, 05:51 PM
I suppose originally they kept the voltage rating so low in order to make the caps smaller, now days that size restraint is no longer an issue.

Radiotronman
10-15-2016, 08:54 PM
I slid the CRT and its heavy mounting bracket out of the cabinet so I could clean the CRT face. Plenty of orange nicotine came off before it got clean and shiny. I also put a little super glue on the CRT socket because it was just a little loose. The focus control came in today so I'll install that while I wait for the caps to come in.

Radiotronman
10-19-2016, 12:43 PM
The main chassis is completely recapped. I still have to recap the small am/fm chassis. I slowly powered it up and have a raster! So far I don't have any video coming through and Ive checked all of the video tubes.

Radiotronman
10-19-2016, 12:45 PM
Here is the main chassis after recapping...

Radiotronman
10-19-2016, 10:35 PM
I wiggled a tuner tube and finally got great fm radio. It looks like video is trying to get through, but no video yet. There is a jack on the back I think is where I would plug in a DVD player or some video source, as the only screw antenna jacks is on the am radio chassis. If you look in the picture it's the little rca style jack in the back center of the chassis. The schematic only shows the table model, which does not show the seperate am chassis. Any thoughts or anyone that has restored this model?

Eric H
10-20-2016, 01:48 AM
The main chassis is completely recapped. I still have to recap the small am/fm chassis. I slowly powered it up and have a raster! So far I don't have any video coming through and Ive checked all of the video tubes.

Interesting that the tube uses an Ion trap yet appears to have an Ion burn? Or am I seeing something else on the screen?

Electronic M
10-20-2016, 07:59 AM
I wiggled a tuner tube and finally got great fm radio. It looks like video is trying to get through, but no video yet. There is a jack on the back I think is where I would plug in a DVD player or some video source, as the only screw antenna jacks is on the am radio chassis. If you look in the picture it's the little rca style jack in the back center of the chassis. The schematic only shows the table model, which does not show the seperate am chassis. Any thoughts or anyone that has restored this model?

That is an antenna jack for the tuner. Dumont used 72ohm (yes I said 72) coax, and an sometimes an RCA jack for it's TV antenna inputs...just get an F to RCA adapter and plug the RF output of your RF modulator into it.

Radiotronman
10-20-2016, 09:55 AM
Eric, I noticed that too about the ion burn on the center if the screen. It's not super noticeable with a raster, but it's there. I'm just happy this oddball CRT tests very strong.

Tom, thanks for that info! I'll get one of those jacks and give it a try!

Radiotronman
10-20-2016, 11:02 AM
I've got my audio locked in and I can almost see the video. Is there not a horizontal frequency control in this set? I only see the horizontal hold control.

Electronic M
10-20-2016, 01:31 PM
Some Dumonts had a nut on top of the H osc transformer can that would act as a coarse hold/H frequency control....If it has the can and there are adjustable slugs that may be worth doing...If no nut I recommend checking the waveform with a scope while adjusting the transfmr.

Radiotronman
10-21-2016, 01:00 AM
The horizontal oscillator transformer in this set has a round disc that you turn with your hand to adjust horizontal hold. I backed it in and out with no locking picture. I'll check resistors around this transformer and in the sync circuits and hopefully find the out of tolerance resistor causing this.

Radiotronman
10-22-2016, 01:37 AM
I replaced several out of tolerance resistors in the horizontal sync and sync clipper areas, but nothing changed. Still can't get the horizontal to lock. Any thoughts?

Eric H
10-22-2016, 03:13 AM
Are you certain you have the correct value capacitor across the horizontal coil? Even if you do you could try changing the value and see if it brings it into range.

I think this is more an issue with the Horizontal Oscillator speed rather than a Sync problem, I would look closely around the 6K6 Osc tube, particularly cap C96 (assuming you're using the Sams?)

Can you make the horizontal flop both directions or does it never reach the point of straightening up?

Radiotronman
10-22-2016, 08:35 AM
It never really straightens out. I can get the lines to get about an inch wide, but never straighten any further. I will look at those caps like you suggested and yes I'm using the sams. Thanks!

Radiotronman
10-22-2016, 02:45 PM
Ok, so I remembered that some sets a horizontal frequency or locking range trimmer on the bottom of the horizontal oscillator transformer. So I pulled the chassis out and underneath a bundle of wires I found this adjustment screw sicking out of the bottom of this transformer. I hooked up all of the cables to the set,and turned it on. Adjusting this screw got this image to finally lock! Now that I have an image, I'll have to figure out why my image is washed out, but at least I have s stable image! I'll post a picture once I get my picture figured out.

Radiotronman
10-22-2016, 04:48 PM
It seems if you turn the set off or change the channel, , the set loses horizontal sync and you have to slide the set out and adjust the trimmer again. Perhaps a 10,000pf mica is leaky around this transformer. Could I replace with a .001 ceramic?

old_coot88
10-22-2016, 06:13 PM
More likely the hor.osc tube is borderline weak, even though it may test 'good' on a tester.

Radiotronman
10-22-2016, 06:31 PM
Ok, I'll try another, thanks!

Radiotronman
10-22-2016, 10:35 PM
This is the best I can get the video. It's obviously blurry and pretty washed out. I've replaced the video output tube(6AG7) and sprayed the socket in the 1st video tube (6AG7), but it hasn't gotten better.

old_coot88
10-23-2016, 12:49 AM
Yee-ikes!:eek: Has anybody played with the IFs?

Radiotronman
10-23-2016, 08:41 AM
I don't know, geez. I guess I'll start there....any tips?

Kevin Kuehn
10-23-2016, 09:57 AM
Have you tried directly injecting a video signal at the video output grid?

old_coot88
10-23-2016, 12:19 PM
I don't know, geez. I guess I'll start there....any tips?
Before touching anything in the IFs, first you need to ascertain that the problem's not in the video chain, i.e., 'downsteam' of the video detector.

Radiotronman
11-07-2016, 06:37 PM
I've been checking every resistor in the video chain with no smoking gun. Tonight I decided to check around the DC Restorer tube(6AL5). I found a 330k resistor that was many times over its value. Popped in a new resistor and was rewarded with a great picture! I've got a few caps left to replace in the separate am radio chassis and to figure out what's wrong with record player. The hardest part of this combo is done though!

Radiotronman
11-07-2016, 10:13 PM
Put in the final caps and put it all back together. Picture quality in this set is excellent!

Phil Nelson
11-08-2016, 01:44 AM
Nice work. Those early DuMonts are the best.

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