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-   -   Dumont RA-113 (B3) restorations (http://www.videokarma.org/showthread.php?t=267583)

Radiotronman 10-28-2016 09:51 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.

bandersen 11-03-2016 04:18 PM

Sorry to hear you got a bad control. Mine just arrived also in their original packing including desiccant. Luckily, both test good :)
https://c3.staticflickr.com/6/5450/3...48eb3f79_z.jpg

Before I install it, I wanted to sort out the sync and sound issues.
https://c4.staticflickr.com/6/5333/3...96986688_z.jpg

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.
https://c8.staticflickr.com/6/5712/3...28dde1c2_z.jpg https://c8.staticflickr.com/6/5748/3...be038a28_z.jpg

The sync circuit has new tubes, paper caps and bad resistors replaced. That left the micas. Sure enough, found some bad ones!
https://c8.staticflickr.com/6/5505/3...d7963252_z.jpg https://c3.staticflickr.com/6/5500/3...9be037bf_z.jpg

That improved things, but still not quite right. Very touch horizontal with some bending.
https://c7.staticflickr.com/6/5625/3...6eb0196d_z.jpg

Continued checking micas and found a bad 270pF off the hor oscillator coil. Bingo!
https://c5.staticflickr.com/6/5588/3...3295f7ba_z.jpg

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.
https://c1.staticflickr.com/6/5610/3...4aab972f_z.jpg

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 :)
https://c2.staticflickr.com/6/5459/3...7ab843ed_z.jpg https://c5.staticflickr.com/6/5456/3...be445514_z.jpg

IsthmusTV 11-04-2016 10:21 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!

-Clark

bandersen 11-04-2016 03:58 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 04:35 PM

Quote:

Originally Posted by bandersen (Post 3172853)
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

Radiotronman 11-06-2016 05:27 AM

Bob, where do you order your mica caps? Some places are incredible high and some have a very limited selection of values.

bandersen 11-06-2016 09:34 AM

Mostly Mouser Electronics and Digi-Key. Yes, they are rather expensive but they have a good selection of values.

bandersen 11-18-2016 12:14 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.

https://c2.staticflickr.com/6/5723/3...f42f273d_z.jpg

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

https://c6.staticflickr.com/6/5792/3...9e24b82f_z.jpg

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!
https://c8.staticflickr.com/6/5777/3...426f0e93_z.jpg

holmesuser01 11-18-2016 01:23 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.

Radiotronman 11-18-2016 07:12 PM

Your Dumonts look great Bob! Gotta posts pictures of them back in the cabinets.

bandersen 11-18-2016 07:22 PM

The owner just dropped off the chassis and he only has one cabinet back at his place. The 2nd chassis is a spare

wa2ise 11-19-2016 02:17 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.
https://c8.staticflickr.com/6/5505/3...d7963252_z.jpg

M3-SRT8 11-26-2016 09:08 PM

Nice work, Bob.

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


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