Sylvania 1-076 arrived!

[jeyurkon]

Originally Posted by bgadow

Look for an old picture tube brightener...a cheap and easy donor.

I should have thought of that! Thanks!

John

[jeyurkon]

Apparently triode CRTs are about as testable as electrostatic CRTs. None of the CRT analyzers that I'm aware of can test them.

I wanted to know the health of the 10MP4 in the Sylvania. I decided to measure the emission by using G1.

At least now I know that the CRT isn't dead. I measured a very high emission, but doing it this way collects most all of the electrons emitted from the cathode rather than the ones that go through the grid. The portion of the cathode that they would originate from could still be weak. You can read about why here http://www.sencore.com/uploads/files/RejuveCRTs.pdf

The Sylvania Technical Manual says that the G1 cutoff is measured by observing the extinction of the focused beam on the screen.

I plan on doing this. I'll need to supply the HV and also be very careful to start with G1 above the cutoff so as not to burn a hole in the screen. If it passes this test then it should be in pretty good shape.

Of course I could just test it in the chassis once I finish cleaning, recapping, and checking all of the resistors. But this is going to take a while and I'd like to know soon whether I need to get it rebuilt or not.

John

[jeyurkon]

I did say I would be slow. Since I couldn't get the CRT loose from the front mount I removed the front plate. That actually was helpful because There is a fiber disk between the focalizer and the yoke. It is tight on the neck of the tube and the tabs caught on the base. That wouldn't have been a problem except that the base is loose so I wanted to be gentle. The front plate helped me keep the CRT aligned while I manipulated the disk.

Now I can remove the bridge and have easy access to clean the chassis as nasadowsk suggested.

John

[damen]

Very Kool tv looking forward to seeing the pics. of it finished.
Good Luck Damen

[jeyurkon]

I'm still making slow progress. Many of the paper caps are difficult to get to, buried under other parts. I found one good paper cap so far. It was the only one that didn't have blisters on the outside. I wonder if that's related.

I've also found quite a few open or out of tolerance resistors in the audio output section.

I started to do a quick check by checking the tube chart resistances given by the SAM's. I quickly learned that this was a waste of time. Many of the resistances given are wrong. The schematic from the same SAM's folder seems to agree with what I measure. It'll be easer just to check the individual resistors and not worry about whether the SAM's got it right.

John

[jeyurkon]

I've replaced all the paper caps and some of the electrolytics. I'm sure I'll get some flak for it but I kept the electrolytics that had better ESR than the replacements and had leakage in the acceptable range.

I cleaned the chassis. It's not as new looking as many of you guys are capable of producing, but if you look at the photos in the early thread, it's an improvement. The dark area around the electrolytics on top is wax that had dripped from the horizontal output choke on the bridge. If I end up rebuilding those electrolytics I'll clean it up then.

I may paint the top of the power transformer, but I'm waiting until I see if I have to apply a hum fix to the transformer. They have you remove the top instead of removing the entire transformer to work on it.

The thing that took the longest was restringing the dial cord for the radio section. It has three idler wheels, drive pulley and capacitor pulley. Only the capacitor pulley is accessible, you have to use hooks to deal with the others all the while maintaining enough tension to keep the cord from falling off. I hope I never have to do that again.

Now I have to work on the bridge which has just as many paper caps.

John

[jeyurkon]

I was hoping to finish up the set tonight. That was too optimistic. There was way too much wrong with the HV section and I need to get some parts.

Originally I claimed there was almost no work done on this set. That was clearly wrong. As I dug into it I found a mixture of high quality repairs and some pretty ham fisted stuff.

The ceramic disc I showed in another thread actually tested good. I replaced it anyhow. The bumble bees were all toast. A 100 ohm wire-wound was open. A 56K 2 Watt reads 100K. The factory manual shows it as 56K, the markings are for 56K, but the Sam's shows it as 5.6K. I bet that might have confused a few people.

I cleaned up the oil that leaked from the 10KV 0.005uF cap.

I removed the HV section from the bridge to make it easier to work on and minimize physical risk to the HV transformer.

There was an incredible cold solder joint on the lead that goes to the feedback winding on the HV transformer. It was just flopping around in the solder around it. I don't know how they managed that because the lead was well tinned. They had a ball of solder about the size of a pea.

I'll post some more photos once I finish the HV and before I install it back into the bridge.

John

[Tony V]

John,
I may have a VM 406 for you. Let me look and if i still have it, i'll let you know.
-Tony

[jeyurkon]

That would be great!
John

[jeyurkon]

I dismounted the bridge and started cleaning it and the chassis. So far no surprises other than a paper cap that has leaked a fair amount of oil

I managed to finaly remove the front plate from the CRT. The rubber pads were glued to it and the support plate. The pads peeled from the glue, but the glue is still on the CRT. I'm going to leave it because it won't be visible and it's too difficult to get off. It's a contact type cement.

There's a long concentric shaft on the tuner. The outper part changes bands and the center tunes. There was oil between them and it has gotten to be very viscous. I don't want to dissassemble it if I don't have to.

I might try the CRC electronic cleaner.

John

[jeyurkon]

Someone who worked on this set previously moved C133 from the bridge down to the main chassis. It connects to pin 6 on the the 6AU6 horizontal control. They took a piece of twin lead and spit it in two and ran that from C133 back up to pin 6.

I can't understand why they did that. It looks like the original electrolytic since it has a Sylvania part number on it. I'm inclined to move it back to the bridge unless someone can come up with a theory as to why it's better in the chassis. The long run to pin 6 seems strange.

The schematic and layout can be found at:

https://www.msu.edu/~yurkon/Sylvania_9-2_Sup2.pdf

John

[bgadow]

Looking good! Very good for the first power up. I've never had a terrible experience with seleniums; they just seem to be "weak" on some sets. (maybe most sets!) I agree, it is fun to get it working the "old way". I was thinking, you might just be the guy to try rebuilding a selenium!

[jeyurkon]

Originally Posted by bgadow

Looking good! Very good for the first power up. I've never had a terrible experience with seleniums; they just seem to be "weak" on some sets. (maybe most sets!) I agree, it is fun to get it working the "old way". I was thinking, you might just be the guy to try rebuilding a selenium!

Actually there are at least still two manufacturers of selenium rectifiers.

I might try putting together a supply with the NOS seleniums and a dummy load to see how they behave. I might have too high expectations for how I think they should test.

But, for now I'm going to use the 1N4007s. and an additional 110 ohms with each.

I'm glad I fused the seleniums in case they died.

John

[jeyurkon]

Well, using the 1N4007s brought the -HV up. I was a little too conservative with the resistors. I'm about 5 volts low, but that shouldn't be a problem.

I saw no change in the performance. The AM radio is working to a degree now without the loop, but that's not related to the -HV since it doesn't use it. It's just that there's a strong AM station in the daytime.

I'm amazed that the set had a picture at all. While trying to figure out why the video was so weak and the AGC wasn't kicking in I discovered that the primary on the first video IF transformer is open. I only had a picture because of the signal bleeding through.

It's probably hopeless to ask, but does anyone have a Sylvania 125-0001 IF transformer? I don't think Merit made a replacement.

I may have to rewind it which would be difficult. It appears to be coated with glyptal which is extremely difficult to remove. On the other hand, the coil shows no signs of having been over heated. It might just be a cold solder joint to one of the terminations.

I suspect that once I get a decent signal through the video IF stages my horizontal problem will take care of itself.

Oh, the CRT HV is 500 volts low. I can only get it up to 9KV. I should be able to get 11KV max and set it to 9.5KV. I think it's because I have a weak 6Y6-G in there. The one in the audio section is better, but it doesn't fit under the coffee can. Which is funny, because it's the Sylvania tube. The weak 6Y6-G that fits is a Philco. I have a 6Y6-GT I can try. I didn't because Wallace's recommends using a coated 6Y6.

John

[jeyurkon]

Here's a photo of the video IF transformer that I need to repair or replace.

John