View Full Version : Dumont RA-113 (B3) restorations

08-19-2016, 11:32 PM
A while back I restored a Dumont RA-113 for two brothers that grew up with the TV. Here's the forum thread:

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. ( (

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. (

RA-113 (

RA-113-B3 (

08-19-2016, 11:42 PM
I decided to tackle the 113-B3 first. (

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. ( (

Both have repairs - some rather ugly :sigh: (

Both also have spliced in HV leads. Same as the previous one I restored. (

08-20-2016, 12:28 AM
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.

Eric H
08-20-2016, 12:38 AM
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?

08-20-2016, 08:27 AM
Nice Bob, no doubt this will be and interesting thread!

Crist Rigott
08-20-2016, 11:22 AM
Looking forward to watching these restorations.

08-20-2016, 12:31 PM
Looking forward to watching these restorations.

Me too...

09-10-2016, 12:49 PM
I finished recapping the B3 chassis. I found convenient tie points for the electrolytics and didn't bother restuffing the cans. (

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. (

The voltages are all high (200 volt bus is 300) but I figure that's to be expected with some power hungry circuits disabled. (

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. (

09-12-2016, 01:01 PM
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. ( ( (

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 :) ( (

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. (

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. (

09-12-2016, 02:29 PM
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? ( (


09-12-2016, 03:10 PM
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.

09-12-2016, 03:50 PM
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!

09-12-2016, 04:08 PM
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.

09-13-2016, 10:54 AM
Do you have a clue as to who supplied the OEM tubes for these DuMonts?

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.

09-13-2016, 02:15 PM
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.

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.

09-13-2016, 02:23 PM
The service info talks about the flyback being an efficient auto-transformer design that has tighter primary/secondary coupling and uses smaller wire gauge.

09-17-2016, 01:30 PM
I went to check voltage around the sync amp and quick realized I neglected to remove the shield and missed some caps :0 (

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.

09-17-2016, 06:05 PM
That can't be good :no: (

Found another cap hiding deep in the bowels. It's the coupling cap between the sync amp and sync clipper. (

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+. (

Yep, sure enough. I connected the 2nd main filter cap to ground when it should be the B- rail. (

Crist Rigott
09-17-2016, 08:14 PM
Very cool Bob.

09-21-2016, 12:40 PM
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 ? (

Phil Nelson
09-21-2016, 01:42 PM
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:

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.


Phil Nelson
Phil's Old Radios

09-21-2016, 02:15 PM
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.

09-22-2016, 09:40 AM
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. ( (

I hope I can get it as clean as Phil's :yes: ( (

09-22-2016, 11:31 AM
My Dumont RA-104's tuning still works, but is sluggish at some points. What did you use for lubricant?

09-22-2016, 11:35 AM
Nothing yet. I just started cleaning it. The Dumont service info recommends Lubriplate #105. Checkout pages 23-24.

09-23-2016, 12:39 PM
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 ? (

Electronic M
09-23-2016, 12:49 PM
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...

Kevin Kuehn
09-23-2016, 01:12 PM
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.

09-23-2016, 01:37 PM
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!

09-23-2016, 05:20 PM
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.

09-24-2016, 01:00 PM
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 ? (

Phil Nelson
09-24-2016, 02:59 PM
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

Electronic M
09-24-2016, 10:36 PM
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.

09-26-2016, 04:01 PM
I love dem DuMonts.:smoke:

09-27-2016, 11:55 AM
While I ponder the pully, I started on the second chassis. It's definitely earlier and a crustier. (

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. (

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. (

09-27-2016, 12:32 PM
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...

09-27-2016, 12:47 PM
They all have three 500 pF HV caps as far as I know. I was referring to the three 470K resistors.

09-27-2016, 03:13 PM
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.

10-13-2016, 10:57 AM
I finished up inside the HV box including a new HV anode lead. Making good progress underneath the chassis now. ( (

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: (

10-13-2016, 12:35 PM
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:

10-27-2016, 10:12 AM
I finished recapping the second chassis and fired it up with an 8XP4 test CRT and substitute yoke again ( (

Noticed a few problems right away.
* No dial lamps and eye tube barely glowing.
* Good FM radio reception, but no sound for TV stations
* No sync
* Power resistor subbing for focus coil cold
* Horizontal periodically "freaks out" (

10-27-2016, 10:24 AM
I quickly solved a few issues. One dial lamp was burned out and the other two had dirty contacts.

The focus control has a large "dead" area. Setting it in a good area gets the sync working better and the brightness/contrast improves. However, the power resistor I'm subbing for the focus coil is now roasting.

Eye tube is totally dark.

Horizontal still freaks out periodically and no sound for TV reception. I'm thinking the sound alignment may be way off.

Also discovered the tuner mounting screws very all very loose and reception cuts out as the fine tuning is adjusted. I bet it's very dirty inside. it will be unmounted,cleaned and lubed.

I'll clean all the controls and tube sockets and swap in some fresh tubes.

Not the worst first power up, but still many issues to resolve.

Need to swap the horizontal yoke leads too. (

10-28-2016, 10:05 AM
Sure enough the focus rheostat is bad :( It has a Dumont poart # and is likely the original. Should be 1250 not 7.8M ! ( (

The break is somewhere near the scratch mark.. (

So with the tap on one side of the break, all the power goes through the 1450 ohm power resistor, on the other side the focus coil which explains why it was sometimes cold and others blazing hot. Either way, the set is being starved of power for the tapped bleeder resistors. (

I'll have to track down a replacement. I'll see if I can dig up a couple 680 ohm power resistors in the meantime as a substitute.
Also tested all the tubes and found a bad 6AB4 and 6J6 in the tuner and two bad 6AU6 in the IF.

The set must have been in a heavy smokers home. All that goo protected the chassis nicely. (

Also discovered this dangling coil near the tuner. That doesn't look good :no: (

10-28-2016, 10:35 AM

Surplus Sales of Nebraska has a 1K 25 Watt wirewound pot that's a good substitute for the focus control, and it's only $8:

Good luck,


10-28-2016, 10:48 AM
Thanks for the tip. Now I'm looking for more goodies there to fill up my order :)

10-28-2016, 10:51 PM
Order at least two of them. I ordered two to meet their minimum order and one of them measured over 3megs. They were both brand new in their vintage packaging too.

11-03-2016, 05:18 PM
Sorry to hear you got a bad control. Mine just arrived also in their original packing including desiccant. Luckily, both test good :) (

Before I install it, I wanted to sort out the sync and sound issues. (

I put a scope to work and found the horizontal synchro waveform looked great, but the synch signal feeding it had a lot of video present. ( (

The sync circuit has new tubes, paper caps and bad resistors replaced. That left the micas. Sure enough, found some bad ones! ( (

That improved things, but still not quite right. Very touch horizontal with some bending. (

Continued checking micas and found a bad 270pF off the hor oscillator coil. Bingo! (

Continued checking micas into the sound circuit and found a bad 47pF on the audio output tube. Damn you micamold! I went ahead and replaced the two other micas caps in the sound IF just for good measure.

Finally, I have sound! Not the best but I expect I need to tweak the sound IF alignment after replacing those caps. (

I also replaced the very worn out eye tube and it's working great now:)
Looks like I'm in the home stretch on this project :) ( (

11-04-2016, 11:21 AM
Looking good, Bob. Maybe I should check those mica caps in mine, particularly the ones in the sound IF.

I bought just one of the SSN rheostats and it was good. I get a kick out of opening 50+ year-old NOS components in the original packaging :yes:

It's nice that those 6AL7 eye tubes are so cheap (I think I paid about $4 a piece for the ones I got). A far cry from a 6E5!


11-04-2016, 04:58 PM
I got a kick of it too. They sure did pack a lot of desiccant in there. The owner of these chassis did me a big favor by including a full set of NOS replacement tubes when he dropped them off. No need to go hunting through my stash in the attic :)

Electronic M
11-04-2016, 05:35 PM
I got a kick of it too. They sure did pack a lot of desiccant in there.

That desiccant sure packs a kick, huh?:beer::drunk::D

11-06-2016, 06:27 AM
Bob, where do you order your mica caps? Some places are incredible high and some have a very limited selection of values.

11-06-2016, 10:34 AM
Mostly Mouser Electronics and Digi-Key. Yes, they are rather expensive but they have a good selection of values.

11-18-2016, 01:14 PM
I replaced the candohm resistors with chassis mount power resistors. Although the originals in this chassis were OK, there were failures in the other two I've worked on. So I figure it's best to replace them. (

Also got the replacement focus control installed. Those big 100 ohm resistors barely even get warm. (

Did a little touch up on the alignment and the sync is even better now. Sound much better too. One of the slots in the thread shafts for the sound IF was spread apart like a screwdriver had been jammed in it. Seems likely someone had tried to improve the sound in the distant past so I wasn't surprised that it needed adjusting.

I also cleaned and lubed the tuner. I'm calling this one done which leaves fixing up the tuner on the other. I'll be glad to get these beasts off my workbench! (

11-18-2016, 02:23 PM
Just seeing how good these sets look in your posts gives me hope that my own RA-113 will look this good when I'm finished with it.

Mine has sound through the tuner, picks up FM just fine, and has HV now. I can hear the vertical oscillator running. Still nothing on the screen, but my CRT tests very good, and is the DuMont original 17BP4.

11-18-2016, 08:12 PM
Your Dumonts look great Bob! Gotta posts pictures of them back in the cabinets.

11-18-2016, 08:22 PM
The owner just dropped off the chassis and he only has one cabinet back at his place. The 2nd chassis is a spare

11-19-2016, 03:17 PM
Micas don't like having DC across them. Usually, in tuned circuits they are in parallel with a coil, thus almost no DC. But I've seen them go bad with as little as 50VDC across them.

11-26-2016, 10:08 PM
Nice work, Bob.

I've used those SSN variable wws in my DuMonts. They work fine.:smoke: