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  #16  
Old 02-01-2009, 10:43 PM
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Quote:
Originally Posted by bgadow View Post
Look for an old picture tube brightener...a cheap and easy donor.
I should have thought of that! Thanks!

John
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  #17  
Old 02-10-2009, 11:01 PM
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10MP4 test

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
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  #18  
Old 02-25-2009, 10:04 PM
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CRT removed

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
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File Type: jpg 10MP4_removed.jpg (79.0 KB, 231 views)

Last edited by jeyurkon; 11-14-2009 at 06:58 PM.
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  #19  
Old 02-25-2009, 10:21 PM
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John,
I may have a VM 406 for you. Let me look and if i still have it, i'll let you know.
-Tony
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  #20  
Old 02-26-2009, 10:30 AM
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That would be great!
John
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  #21  
Old 02-28-2009, 09:08 PM
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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
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  #22  
Old 03-08-2009, 10:24 PM
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Electrolytic relocation

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
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  #23  
Old 03-09-2009, 12:10 AM
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Very Kool tv looking forward to seeing the pics. of it finished.
Good Luck Damen
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  #24  
Old 03-15-2009, 08:47 PM
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Some progress

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
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  #25  
Old 03-26-2009, 10:57 PM
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Chassis Photos

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
Attached Images
File Type: jpg C15_Top_Cleaned.jpg (72.9 KB, 32 views)
File Type: jpg C15_Bottom_Cap.jpg (106.0 KB, 31 views)

Last edited by jeyurkon; 11-14-2009 at 06:59 PM.
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  #26  
Old 04-01-2009, 11:09 PM
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Coffee Can HV

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
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  #27  
Old 04-05-2009, 10:54 PM
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RF HV and Bridge recap photos

I've finished recapping the Coffee Can HV and the bridge. Now I just need to reassemble everything and hope for the best.

The first photo is the back of the RF HV module. The long white capacitor is a 10KV 0.0005uF film cap.

The second photo shows the back of the bridge with the coffee can HV mounted back on to it. On the top between the yellow film capacitor and the black electrolytic there is what looks like a paper cap. That actually is a polystyrene capacitor and has unmeasurable leakage. I decided to leave it in since it didn't seem to be following the fate of the paper caps.

John
Attached Images
File Type: jpg RF_HV_back.jpg (141.5 KB, 37 views)
File Type: jpg Bridge_Back.jpg (79.1 KB, 39 views)

Last edited by jeyurkon; 11-14-2009 at 07:01 PM.
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  #28  
Old 04-08-2009, 09:13 PM
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Bad Horizontal Center pot

I was hoping to power the set up tomorrow. That won't happen now. While cleaning the controls I discovered that the Horizontal Center pot was bad. I opened it up hoping to repair it but it's beyond repair. It's a 140 ohm 2W wire-wound panel mount. 43-140CT by clarostat. The wire was blown in numerous spots. It must have seen a very high current to do that.

I think the closest I'm going to find is a 150 ohm 2 watt composition pot that I found at Newark. I'm going to go ahead and order that. If anyone should have something more appropriate they'd be willing to part with please let me know.

John
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  #29  
Old 04-09-2009, 09:19 AM
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What about the selenium rectifiers?
They need replacing as well...
Bill Cahill
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  #30  
Old 04-09-2009, 07:45 PM
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Quote:
Originally Posted by Bill Cahill View Post
What about the selenium rectifiers?
They need replacing as well...
Bill Cahill
One of the dangers of posting progress; I was afraid someone would notice that.

The selenium rectifiers form a center-tapped full wave -125 VDC supply. There is a 39 ohm resistor in series with each rectifier. I believe they're there to limit in-rush current. They won't protect the transformer if the seleniums short.

The output of the supply is already fused. I intend to put a fuse in series with the 39 ohm resistors to protect the transformer.

On our original set we had to replace the seleniums once in its lifetime.

As long as the transformer is protected, I'm not worried. I have a lifetime supply of selenium rectifiers and if I have to change them every 5 years or so I don't have a problem with that. They're easy to get to and change.

I can't explain why I want to keep them in use anymore than I can explain why I want to watch a 60 year old TV. Maybe I just like the smell of garlic.

John
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