Dumont RA-113 (B3) restorations
 

A while back I restored a Dumont RA-113 for two brothers that grew up with the TV. Here's the forum thread: http://www.videokarma.org/showthread.php?t=259542

Little did I know they were so happy with the set they set out to find another. Flash forward to a few months ago when they contacted me that they not only found another 113 but a share chassis as well.

This time around, they only pulled the chassis and one speaker and left the picture tube and yoke inside the cabinet. Here they are up on the workbench.

https://c2.staticflickr.com/9/8691/2...14f02940_c.jpg

https://c8.staticflickr.com/9/8695/2...082c36a8_c.jpg

The one on the right tuns out to be a RA-113-B3 variation. The other has a depression on the chassis for what I assume is a large metal cone CRT.
https://c3.staticflickr.com/9/8490/2...9ee6b958_c.jpg

RA-113
https://c8.staticflickr.com/9/8703/2...2b7df2d8_z.jpg

RA-113-B3
https://c6.staticflickr.com/9/8686/2...6e726e9c_z.jpg

I decided to tackle the 113-B3 first.
https://c4.staticflickr.com/9/8174/2...f053bf74_c.jpg

There are quite a few differences between the two. Components, values, wiring, etc.

For example, here's the rear chassis of the 113 on the left and 113-B3 on the right.
https://c5.staticflickr.com/9/8852/2...26658813_c.jpg https://c2.staticflickr.com/9/8408/2...656dc2b9_c.jpg

Both have repairs - some rather ugly :sigh:
https://c5.staticflickr.com/9/8396/2...3cb80373_z.jpg

Both also have spliced in HV leads. Same as the previous one I restored.
https://c7.staticflickr.com/9/8327/2...9461e135_c.jpg

Those are great sets Bob. I have had the chance to get one near me, but I haven't been willing to splurge on it.

I wonder if the HV leads were changed because they had the oddball Dumont snap type connector, and the CRT had been replaced with one that had the standard cavity type connector?

Nice Bob, no doubt this will be and interesting thread!

Looking forward to watching these restorations.

Me too...

I finished recapping the B3 chassis. I found convenient tie points for the electrolytics and didn't bother restuffing the cans.

https://c8.staticflickr.com/9/8624/2...5c666bf5_c.jpg

Still haven't found a yoke yet, but I wanted to try a power up. So I popped out the hor. and vert. output tubes and subbed in a power resistor for the focus coil.
https://c5.staticflickr.com/9/8778/2...da976559_c.jpg

The voltages are all high (200 volt bus is 300) but I figure that's to be expected with some power hungry circuits disabled.
https://c5.staticflickr.com/9/8276/2...53b570ed_c.jpg

After a bit of control fiddling, I was able to get some deent FM radio reception. Now to dig up a yoke and recap inside the HV box.
https://c8.staticflickr.com/9/8295/2...21e04080_c.jpg

I popped the cover off the HV cage for a closer look. It appears the flyback has been replaced. The three HV caps were replaced with 470pF ceramic caps rated for 15kV.
https://c4.staticflickr.com/9/8730/2...aec1d560_c.jpg

https://c7.staticflickr.com/9/8309/2...fc7e1020_c.jpg

https://c7.staticflickr.com/9/8169/2...110cbf58_c.jpg

I scavenged a suitable yoke from an Admiral and fired it up. I could hear the horizontal oscillator kick in and after a bit of control tweaking got a raster :)
https://c3.staticflickr.com/9/8205/2...36094c68_c.jpg

https://c5.staticflickr.com/9/8367/2...55aac947_c.jpg

This is the best I could get after going through all the various horizontal adjustments. The free running frequency and synchro waveform look OK. I'm thinking it's a problem in the sync separator circuit.
https://c7.staticflickr.com/9/8449/2...928f70c8_c.jpg

The video looks sharp so I'm hoping for a real nice picture soon as I can sort out the hor. hold issue. Also upside-down and backwards but that just requires some lead swapping.
https://c7.staticflickr.com/9/8489/2...920bd4e6_c.jpg

Nice work as usual, Bob. Takes me back to three years ago when I was restoring mine. I also opted to install the electrolytics under the chassis. Maybe I could have saved some money and used ceramic HV caps in mine :scratch2: Are you doing the other chassis at the same time?

http://i1216.photobucket.com/albums/...ps03e73005.jpg
http://i1216.photobucket.com/albums/...ps9d5db654.jpg

-Clark

The ceramic caps seem to work well. I used them in another RA113 a few years ago and it's still running fine. I haven't started work on the other chassis yet. I'll try to get this one sorted out first, but if I get stuck may switch to the other for a while.

Do you have a clue as to who supplied the OEM tubes for these DuMonts?

My RA-113 is full of every brand known. I suspect that RCA supplied them, but don't really know.

I've replaced all but 3 or 4 electrolytic capacitors in mine. I've got FM radio to the speaker, but still have not seen a raster on the 17BP4 tube, which checks good with my tester. I'm not worried, though, as every cap I've replaced has made a difference in the way the chassis works. Just replacing those 3 HV caps on this set raised the HV from 1500v to 10,000v!

Don't know bout the tubes. This chassis had one Dumont branded 6AU6 while the rest were a mix. Some relatively new and most tested very good. That along with the replaced flyback makes me think it might have been regularly serviced or had a major overhaul.

Mine also came to me with tubes of several different brands, so I can't shed any light on the subject. The 17BP4 is DuMont branded, though.

My RA-113 (5) is my 3rd DuMont. Had an RA-111, and another that I had when I was a kid. I couldn't get the first one to do anything other than light the tubes. It had been in an abandoned house and had been rained on.

I've never seen a replacement flyback for these. The flyback in my 113 runs very cool. I let it run for an hour, watching everything like a hawk, and after I turned it off and discharged the CRT, there was almost no heat from the doughnut.

The service info talks about the flyback being an efficient auto-transformer design that has tighter primary/secondary coupling and uses smaller wire gauge.

I went to check voltage around the sync amp and quick realized I neglected to remove the shield and missed some caps :0
https://c6.staticflickr.com/9/8542/2...60b36d42_c.jpg

That are is the sync amp and separator so I've got my fingers crossed I found the problem. Going to recap right now and give it another power up.

That can't be good :no:
https://c4.staticflickr.com/9/8108/2...a9933f05_c.jpg

Found another cap hiding deep in the bowels. It's the coupling cap between the sync amp and sync clipper.
https://c3.staticflickr.com/9/8530/2...1f236071_c.jpg

OK, that got the sync working, but now I have horrible bending and brightness bars. I figure there must be some major hum in the b+.
https://c8.staticflickr.com/9/8784/2...98d7e9a3_c.jpg

Yep, sure enough. I connected the 2nd main filter cap to ground when it should be the B- rail.
https://c7.staticflickr.com/9/8371/2...569c3cb5_c.jpg

Very cool Bob.

The tuner contacts seems a little dirty and might benefit from a little cleaning but I'm not sure how to get it open. I think I need to turn four little clasps on top, but it seems other stuff will prevent it from coming off. Even if I pull the three tubes and shields, it look like the coil will be in the way.

Am I missing something? Has anyone else opened up one of these while it was mounted in the chassis ?

https://c7.staticflickr.com/9/8304/2...5fed925e_c.jpg

I'm afraid you need to unsolder a few connections and pull the tuner. This article has some long bits about cleaning & lubricating an RA-113 tuner:

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

Start at, "Removing the Tuner."

Every inductuner that I've looked at had considerable petrified grease, etc., inside, so it's a good long-term strategy to clean & re-lube everything, even if the tuner turns at the moment.

Regards,

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

http://antiqueradio.org/art/DuMontRA...sInstalled.jpg

OK, I was afraid you might say that ;) Between your excellent, detailed writeup and the second chassis for reference I should be able to manage it.

I managed to get it out without too much fuss. I'm going to try and keep the dial attached so I can avoid restringing.
https://c8.staticflickr.com/9/8053/2...2c881949_c.jpg

https://c8.staticflickr.com/9/8141/2...9cc67acd_c.jpg

I hope I can get it as clean as Phil's :yes:
https://c2.staticflickr.com/9/8065/2...a572b513_c.jpg

https://c3.staticflickr.com/9/8764/2...522360a3_c.jpg

My Dumont RA-104's tuning still works, but is sluggish at some points. What did you use for lubricant?

Nothing yet. I just started cleaning it. The Dumont service info recommends Lubriplate #105. Checkout pages 23-24.

http://www.earlytelevision.org/pdf/d...es_ra-111a.pdf

There's a stiff steel wire wrapped around the horizontal hold control shaft that makes it hard to turn. The other chassis doesn't have it but I think I may have seen something like it in the past on other chassis.

I'm guessing it's there to ground the shaft or perhaps stiffen it up so the shaft doesn't move if the knob is accidentally bumped.

Anyone seen something like this before ?

https://c8.staticflickr.com/9/8386/2...5f52b87d_c.jpg

Could also be a spring from elsewhere that a previous repair guy put there so as not to loose, and then forgot to reinstall where it belongs...

It appears to me that someone made it to hook over the top edge of that chassis. My guess is a tech did it to satisfy a customers request for a more tamper proof Horizontal Hold control.

I just reviewed the service notes and see that the inner control is volume/power! How odd to combine one of the most used controls with one of the least used. I sure wouldn't want the hold control moving when I adjusted the volume!

That is strange, probably why that spring is there, because the on/off volume does move that control some. I've never seen that combination before.

Making good progress with the cleaning but noticed that a pulley appears to be missing. The other tuner has it and without it, the dial cord rubs at some dial positions.
Not sure what might have happened to the old one or how to replace it :scratch2: The shaft is riveted on and I really don't want to remove it if possible. Maybe a nylon pully could be mushed over the end ?
https://c5.staticflickr.com/9/8496/2...307ce6b9_c.jpg

Maybe you could grind the head off that shaft with a Dremel tool, slip on a new pulley, and epoxy a little round piece of metal or plastic back on to replace the head. Tape the string farther down the shaft and out of the way to avoid cutting it.

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

Rather than try and glue the metal back on I'd try to drill and tap it so I could screw a washer down to replace the head.

I love dem DuMonts.:smoke:

While I ponder the pully, I started on the second chassis. It's definitely earlier and a crustier.
https://c6.staticflickr.com/9/8770/2...dd6ddb7c_c.jpg


First I pulled the 5U4 and did a power up test. All the tubes lit and I have about 860 VAC on the 5U4 plates.
https://c8.staticflickr.com/6/5317/2...cdcf4f05_c.jpg

I'm going to start in the HV box this time around. This one has three 470K resistors in series while the other had a single 2M HV resistor.
https://c3.staticflickr.com/9/8486/2...5092807d_c.jpg

So, the one with the 3 470 caps are the early version? I wasn't sure where my RA-113 came in the model run. I got those 3 caps from Just Radios in Canada.

The replacement of these 3 brought the HV up from 1500v to 9000v.

I'm enjoying reading about the restorations here.

EDIT: I must be losing it. I started out thinking about those 3 resistors, and somehow, while typing, I switched to the capacitors and what happened when I replaced them. It's been a long day, so far...

They all have three 500 pF HV caps as far as I know. I was referring to the three 470K resistors.

OOPS! So was I. I started thinking about the 3 caps and... well.... I'll go back and fix the boo boo.

I finished up inside the HV box including a new HV anode lead. Making good progress underneath the chassis now.
https://c5.staticflickr.com/9/8557/3...da74df71_z.jpg https://c5.staticflickr.com/6/5694/3...ca9aa66e_z.jpg

This one is much dirtier and crustier than the other. The wiring insulation is rather brittle so I'm having to be more careful. There is also a difference in component type, placement and tube wiring. For example, this 0.01uF cap was a conventional looking paper cap in the other set. I'm pretty sure this is also a paper cap housed in a mica looking package.

The biggest headache so far is the vertical oscillator. The 6SN7 dual triode wiring is flip-flopped from what's shown in the schematic and the circuit is a little different :sigh:

https://c5.staticflickr.com/6/5672/3...d589b963_z.jpg

Those paper "micas" can be deceptive.

When in doubt, I check the parts lists for descriptions and see if any of the replacement parts have an "M" in them or not.

I tend to shotgun ANY caps in the horizontal circuits now.:smoke: