Dumont RA113 "Burlingame" restoration

[kvflyer]

Originally Posted by bandersen

... and some resistors almost double the resistance they should be.

"Now there's a surprise!" Glad you checked Bob. But, I was sure that you did.

[bandersen]

What was a little surprising is that all the larger valued resistors (10K and up) were within spec. It's the smaller (< 500 ohm) resistors that were way off. I've seen the same in some early Admiral sets.

[Findm-Keepm]

Originally Posted by bandersen

What was a little surprising is that all the larger valued resistors (10K and up) were within spec. It's the smaller (< 500 ohm) resistors that were way off. I've seen the same in some early Admiral sets.

The failure mode of most carbon composition resistors is moisture absorption - the carbon particles absorb moisture, causing the particles to separate, and forming a higher resistance bond. It's noticed more greatly in small, sub 1K values, as the shift is tens or hundreds of ohms, a large percentage of the original value. This is typical whether on the shelf, or installed in equipment.

No manufacturer was ever able to eliminate moisture as a problem. IRC tried, and got a patent for their "molded" carbon composition resistor process that sealed the outside of the resistor and thus reduced moisture intrusion, but aging and lead flex allowed the moisture intrusion.

If it wasn't for economy and pulse/surge capability, carbon composition resistors would have been dead long ago, as most film types suck at handling surges.

And no, you can't bake the moisture out - DoD and NASA both tried, but found that the heating process shifted resistance greater than the moisture did.

Cheers,

[bandersen]

I recently purchased some carbon comps from Allied Electronics for those "special" sets where I'd like to retain the original look. Also, they were dirt cheap

Check out the bag they came in.


Along with the 1/2w 100K resistors inside was this humidity strip and some silica gel desiccant.


It seems to have helped. Every resistor is +/- 5% with a bunch being under 100K.


I spot checked a few from my non-environmentally sealed stash and all are high but still just within tolerance.

[IsthmusTV]

Those same two resistors (68 Ohm and 270 Ohm) were way high in mine, too. I have also had to replace very few resistors in this set. I see that you also had only two paper caps in the little shielded compartment. Phil Nelson's had three


-Clark

[Kamakiri]

Before I forget, would you mind taking a quick shot of the tuner string when you get a moment? On the one I'm doing, it seems to have slipped, and the knot came out of place on the shaft.

[bandersen]

I finished replacing the main power supply filter caps which just leaves two multi-section caps to go. I figure that was good enough and decided to fire it up.

No smoke and I could hear the horizontal kick in. No raster though. I loosened up the anode cap and was able to draw a nice strong arc.

Eventually, I noticed that the test CRT filament wasn't lighting up and touch up the pins with a soldering iron. That did the trick

Unfortunately, I only seem to have horizontal deflection and I can heard some corona arcing inside the HV box but it's progress of sorts.

Originally Posted by Kamakiri

Before I forget, would you mind taking a quick shot of the tuner string when you get a moment? On the one I'm doing, it seems to have slipped, and the knot came out of place on the shaft.

Does this help ?

[Kamakiri]

Sort of. The string has a knot which fits into the center. I need to see which way it wraps around the shaft....clockwise or counterclockwise from the center, out.....

[bandersen]

I think I'd need to remove the dial face to show that part ? Not so easy to do.

[Kamakiri]

Nope, just pull off the knob and give me a shot showing where the dial cord goes when it comes off the center of that geared shaft

[bandersen]

Do these help ?

http://www.flickr.com/photos/70039806@N00/11018689726

http://www.flickr.com/photos/70039806@N00/11018600645

http://www.flickr.com/photos/70039806@N00/11018846204

http://www.flickr.com/photos/70039806@N00/11018773616

[Phil Nelson]

Look at the second stringing diagram (page 6-8) in the Rider manual for RA-112:

http://www.earlytelevision.org/pdf/d...-rider-tv6.pdf

I believe that's what I looked at when I restored my RA-113. My tuner had a busted gear, so I had to pull the mechanism completely apart, and somehow I got it back together correctly.

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

[bandersen]

The vertical oscillator definitely isn't running and I've got some weird voltage readings on the osc tube. The plate is -55 volts but should be 70 Could be the boosted B+ line isn't working right.

[bandersen]

I discovered a loose wire in the B+ Boost circuit. Fixing that resulted in a raster


I rigged up a crude antenna and picked up this LPTV broadcast. The focus is terrible because the focus coil messes up the self focusing 8XP4 test CRT.


Hooked up to an ATSC receiver / converted box. Zero audio. However, the FM radio reception is pretty good. It wouldn't be the first time a vintage TV didn't like my converter box.


I dug out an unmarked, rebuilt 17" CRT and hooked it up.


This is the best focus I could manage. Could be this CRT isn't compatible with this set or maybe the focus circuit needs some work.

[Kamakiri]

Thanks for the pics and reference materials. I got it

Seems that the tuner was rewound incorrectly at some point, and the tensioner was stuck on the tuner shaft. Working now!