Starting work on the Sylvania 7140M - Videokarma.org TV - Video

***Eric H*** · #1 01-10-2011, 01:29 AM

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 · #2 01-10-2011, 05:39 AM

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

jeyurkon · #3 01-10-2011, 09:28 AM

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

John

miniman82 · #4 01-10-2011, 10:36 AM

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 · #5 01-10-2011, 11:04 AM

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 · #6 01-10-2011, 11:18 AM

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

***Eric H*** · #7 01-11-2011, 12:22 AM

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.

heathkit tv · #8 01-11-2011, 12:38 AM

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

JoeNewberry · #9 01-11-2011, 01:23 AM

Quote:

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.

Sandy G · #10 01-11-2011, 03:23 PM

Quote:

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 · #11 01-11-2011, 04:28 PM

Ach! Ist nazty durty! Nicht gut!

bandersen · #12 01-11-2011, 04:34 PM

It looks great and I don't thinks it's your imagination. That old metal oxide dust is very irritating.

***Eric H*** · #13 01-12-2011, 01:33 AM

The tuner on this is odd too.

The smallest shaft seems to be the fine tuning, string driven inside the tuner.
The largest shaft is for the band switch and the middle shaft is for changing the channels, also string driven. It's really just a two speed setup with the fine tuning having a higher "gear" reduction than the channel changer.

My question is what does the lever with the spring do? It seems to just rock back and forth on the outside of the band switch shaft.

I suppose it might be obvious if I dug the knobs out of the inside of the cabinet and put them all on but I'm feeling pretty lazy so I'm just asking.

I'm guessing some kind of stop, but why the spring, which only operates in one direction by the way.