Starting work on the Sylvania 7140M

[Eric H]

This is the set I won at a local auction a month or so ago.

First thing I wanted to do is see how well the CRT held up, it hasn't been tested for a month so after pulling the chassis I hooked it up to the B&K 466, it didn't shoot up immediately to good, it took maybe 10-15 seconds but it ultimately went up to the top of the scale in less than a minute so i'd say it's pretty good!

Next, after removing the CRT from the chassis I wanted to clean off the heavy Cadmium Oxide crud, this stuff is highly irritating and very toxic.
I put down paper towels and sprayed it with cleaner, most of it was so loose and dusty it just rinsed right off, a toothbrush took care of the rest.

I pulled all the tubes and put them in a box to clean and test later.

I had noticed from looking at the schematic that this set used a very unusual set of tubes to rectify the high voltage, something I've never seen before in a set this old, it uses a pair of 5642 rectifier tubes.

I had to look those up because I had no idea what they were, turns out they are very small tubes that are soldered in place on the back of what I think is the flyback, I didn't take it far enough apart to see what that looks like.

I'll take the chassis to work to clean the rest of it off, it's just regular dirt that's left and the chassis seems to be very nice underneath it all.

[Sandy G]

Wow....Those look like the little "Peanut/Pencil" tubes in a PRC-6 Korean War era walkie-talkie...

[jeyurkon]

I have some 5642 tubes if yours turn out to be weak.

John

[miniman82]

I had a Sony portable transistor set that used HV rectifiers like that, I think I still have the tubes somehwere if you need.

[droptop]

I had a Scott table top set using the Philips Protelgram system. Part of it was a hermetically sealed oil filled can containing the high voltage transformer, caps and three tubes in a tripler configuration that looked similar to those tubes although there was no marking on them. There was no HV from the system so I opened it up to find one tube bad. This system was driven by a 1KC oscillator and was noticeably noisy in operation. I used a modern SS tripler to get it working but eventually found an original replacement and got the set back to original form. Wish I still had it….

[leadlike]

I believe I have a pair of those 5462 rectifiers as well, pulled from a Tektronix scope.

[Eric H]

I finished cleaning the chassis today, the front section was Cadmium plated and severely oxidized, it's terribly toxic and it would come off on my hands every time i touched it, my throat got raw feeling whenever I got near it, (though that may have been mostly my imagination).

I took the entire front section off, it only involved unbolting the tuner and unsoldering a half dozen wires, cleaned it with Rust Remover and painted it with Silver paint. I cleaned the tuner contacts and lubed the tuner shaft.

This process also unavoidably removed the stamped inspection markings and a paper warning label but I took good clear pictures of those and will print them out and glue them on in the same locations.

[Sandy G]

Originally Posted by Eric H

I finished cleaning the chassis today, the front section was Cadmium plated and severely oxidized, it's terribly toxic and it would come off on my hands every time i touched it, my throat got raw feeling whenever I got near it, (though that may have been mostly my imagination).

I took the entire front section off, it only involved unbolting the tuner and unsoldering a half dozen wires, cleaned it with Rust Remover and painted it with Silver paint. I cleaned the tuner contacts and lubed the tuner shaft.

This process also unavoidably removed the stamped inspection markings and a paper warning label but I took good clear pictures of those and will print them out and glue them on in the same locations.

Yeah, well, ya gotta do what ya gotta do...I DETEST a nasty dirty filthy chassis, it just offends my Germanic sense of order...

[heathkit tv]

Ach! Ist nazty durty! Nicht gut!

[heathkit tv]

Add just one more of those tubes and you could go back and buy a brand new CT-100

[JoeNewberry]

Originally Posted by heathkit tv

Add just one more of those tubes and you could go back and buy a brand new CT-100

So that's where Doc Brown got the idea.

[Eric H]

Originally Posted by heathkit tv

Add just one more of those tubes and you could go back and buy a brand new CT-100

If my rectifier tubes light up like a Flux Capacitor I'd better replace them!
Anyway this set can only take me back as far as 1950.

[GeorgeJetson]

Originally Posted by Eric H

If my rectifier tubes light up like a Flux Capacitor I'd better replace them!
Anyway this set can only take me back as far as 1950.

1950's as far back as anyone need go!

Just don't alter the future for your own personal gain by buying a Grays sports almanac.

[Eric H]

All the cans are re stuffed and about half or slightly more of the paper caps have been replaced.

There are still three small axial Lytics under the chassis to be replaced.
Perhaps later this evening I'll be ready for a test run.

I found the green corroded leads of a 150 ohm 3w resistor that had completely fallen off, I don't know where the rest of it went, I never saw it when I removed the chassis. It went to one of the Filters so it's probably important, could explain why it was totally non functional.

[Eric H]

I finished the recapping tonight and have been working on the set for the last 4 hours.

I complicated matters somewhat by leaving a capacitor unconnected at one end and forgetting to solder the ground wire on one of the stuffed cans but I did finally get a picture on it, not a very good one either.

The HV rectifiers must be weak, the HV drops like a stone when the brightness is turned up, either that or the .001@10k ceramic caps aren't a very good sub for the .0005@10k Sprague paper caps, I would think they should be fine since they are double the value and are just for the doubler circuit.

I went ahead and bought a couple NOS Sylvania 5642's to put in it, they were only $4 each.

The Flyback setup on this set is more than a little bit of a pain in the butt to work on, you have to unbolt the yoke to remove the cage since it's all one piece.

The other problem I noticed is the Phasing is off, I have a picture split right down the middle with the left half on the right side and the right side on the left, oh well, one step at a time.