Dumont RA-113 (B3) restorations - Videokarma.org TV - Video

bandersen · #1 08-19-2016, 10:32 PM

A while back I restored a Dumont RA-113 for two brothers that grew up with the TV. Here's the forum thread: 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.

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

bandersen · #2 08-19-2016, 10:42 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

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

Radiotronman · #3 08-19-2016, 11:28 PM

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*** · #4 08-19-2016, 11:38 PM

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?

kvflyer · #5 08-20-2016, 07:27 AM

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

Crist Rigott · #6 08-20-2016, 10:22 AM

Looking forward to watching these restorations.

kvflyer · #7 08-20-2016, 11:31 AM

Quote:

Originally Posted by Crist Rigott

Looking forward to watching these restorations.

Me too...

bandersen · #8 09-10-2016, 11:49 AM

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.

bandersen · #9 09-12-2016, 12:01 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.

IsthmusTV · #10 09-12-2016, 01:29 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

Are you doing the other chassis at the same time?

-Clark

bandersen · #11 09-12-2016, 02:10 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.

holmesuser01 · #12 09-12-2016, 02:50 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!

bandersen · #13 09-12-2016, 03:08 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.

IsthmusTV · #14 09-13-2016, 09:54 AM

Quote:

Originally Posted by holmesuser01

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.

holmesuser01 · #15 09-13-2016, 01:15 PM

Quote:

Originally Posted by bandersen

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.